# This is gd 2.0.1 BETA.

If you have problems, report them in detail, and consider using gd 1.8.4 until gd 2.0 final is out.

The gd 2.0 documentation update is not complete, but most new features are documented to some degree and the what's new section is reasonably complete. Enjoy!

## gd 2.0.1

### A graphics library for fast image creation

### Follow this link to the latest version of this document.

> HEY! READ THIS! gd 2.0.1 creates PNG, JPEG and WBMP images, not GIF images. This is a good thing. PNG is a more compact format, and full compression is available. JPEG works well with photographic images, and is still more compatible with the major Web browsers than even PNG is. WBMP is intended for wireless devices (not regular web browsers). Existing code will need modification to call gdImagePng or gdImageJpeg instead of gdImageGif. Please do not ask us to send you the old GIF version of GD. Unisys holds a patent on the LZW compression algorithm, which is used in fully compressed GIF images. The best solution is to move to legally unencumbered, well-compressed, modern image formats such as PNG and JPEG as soon as possible.

> gd 2.0.1 requires that the following libraries also be installed:

> libpng (see the libpng home page)

> zlib (see the info-zip home page) zlib

> jpeg-6b or later, if desired (see the Independent JPEG Group home page)

> If you want to use the TrueType font support, you must also install the FreeType 2.x library, including the header files. See the Freetype Home Page, or SourceForge. No, I cannot explain why that site is down on a particular day, and no, I can't send you a copy.

> If you want to use the Xpm color bitmap loading support, you must also have the X Window System and the Xpm library installed (Xpm is often included in modern X distributions).

> Please read the documentation and install the required libraries. Do not send email asking why `png.h` is not found. Do not send email asking why `libgd.so` is not found, either. See the requirements section for more information. Thank you!

### Table of Contents

- Credits and license terms
- What's new in version "XYZ" of GD?
- What is gd?
- What if I want to use another programming language?
- What else do I need to use gd?
- How do I get gd?
- How do I build gd?
- gd basics: using gd in your program
- webpng: a useful example
- Function and type reference by category
- About the additional .gd image file format
- Please tell us you're using gd!
- If you have problems
- Alphabetical quick index

Up to the Boutell.Com, Inc. Home Page

### Credits and license terms

In order to resolve any possible confusion regarding the authorship of gd, the following copyright statement covers all of the authors who have required such a statement. If you are aware of any oversights in this copyright notice, please contact Thomas Boutell who will be pleased to correct them.

    COPYRIGHT STATEMENT FOLLOWS THIS LINE

> Portions copyright 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 by Cold Spring Harbor Laboratory. Funded under Grant P41-RR02188 by the National Institutes of Health.

> Portions copyright 1996, 1997, 1998, 1999, 2000, 2001 by Boutell.Com, Inc.

> Portions relating to GD2 format copyright 1999, 2000 Philip Warner.

> Portions relating to PNG copyright 1999, 2000 Greg Roelofs.

> Portions relating to libttf copyright 1999, 2000 John Ellson (ellson@graphviz.org).

> Portions relating to JPEG and to color quantization copyright 2000, Doug Becker and copyright (C) 1994-1998, Thomas G. Lane. This software is based in part on the work of the Independent JPEG Group. See the file README-JPEG.TXT for more information.

> Portions relating to WBMP copyright 2000 Maurice Szmurlo and Johan Van den Brande.

> Permission has been granted to copy, distribute and modify gd in any context without fee, including a commercial application, provided that this notice is present in user-accessible supporting documentation.

> This does not affect your ownership of the derived work itself, and the intent is to assure proper credit for the authors of gd, not to interfere with your productive use of gd. If you have questions, ask. "Derived works" includes all programs that utilize the library. Credit must be given in user-accessible documentation.

> This software is provided "AS IS." The copyright holders disclaim all warranties, either express or implied, including but not limited to implied warranties of merchantability and fitness for a particular purpose, with respect to this code and accompanying documentation.

> Although their code does not appear in gd 2.0.1, the authors wish to thank David Koblas, David Rowley, and Hutchison Avenue Software Corporation for their prior contributions.

    END OF COPYRIGHT STATEMENT

### What is gd?

gd is a graphics library. It allows your code to quickly draw images complete with lines, arcs, text, multiple colors, cut and paste from other images, and flood fills, and write out the result as a PNG or JPEG file. This is particularly useful in World Wide Web applications, where PNG and JPEG are two of the formats accepted for inline images by most browsers.

gd is not a paint program. If you are looking for a paint program, you are looking in the wrong place. If you are not a programmer, you are looking in the wrong place, unless you are installing a required library in order to run an application.

gd does not provide for every possible desirable graphics operation. It is not necessary or desirable for gd to become a kitchen-sink graphics package, but version 2.0 does include most frequently requested features, including both truecolor and palette images, resampling (smooth resizing of truecolor images) and so forth.

### What if I want to use another programming language?

Not all of these tools are necessarily up to date and fully compatible with 2.0.1.

#### Perl

gd can also be used from Perl, courtesy of Lincoln Stein's GD.pm library, which uses gd as the basis for a set of Perl 5.x classes. Highly recommended.

#### Tcl

gd can be used from Tcl with John Ellson's Gdtclft dynamically loaded extension package. (Gdtclft2.0 or later is needed for gd-1.6 and up with PNG output.)

#### Pascal

Pascal enthusiasts should look into Michael Bradbury's gdfp package.

#### Haskell

A new gd interface is now available for Haskell programmers.

#### REXX

A gd interface for the REXX language is available.

#### Any Language

There are, at the moment, at least three simple interpreters that perform gd operations. You can output the desired commands to a simple text file from whatever scripting language you prefer to use, then invoke the interpreter.

- tgd, by Bradley K. Sherman
- fly, by Martin Gleeson

### What's new in version 2.0.1?

- Workaround for a bug in gcc, apparently found in gcc 2.7.2 and up. I reproduced and fixed it while using gcc 2.9.5.2. The bug occurred only when the -g option was in use. This problem caused gcc to spew internal error messages unrelated to the correctness of the code in gd_gd2.c. Howard Jones was first to report it.
- gdImageFilledEllipse documented and altered; no longer requires a superfluous style argument. Thanks to Francis James Franklin.
- The Makefile now offers the correct syntax for optionally creating a static library. Thanks to Jean-Lous Regez, among others.
- A nested comment, an attempt to return the value of a void function, and a potentially significant error in gdImageCopyResampled were fixed thanks to Joseph Shirley.
- A bug preventing proper truecolor text rendering was fixed, thanks to Jason Gallagher.
- gdImageStringFT (FreeType) should now work better against a transparent or semitransparent background, and should act in a manner consistent with the most recent gdImageAlphaBlending setting. Antialiasing is now done via the alpha channel mechanism if the image is a truecolor image.
- Bugs in the output of gdImageArc and gdImageFilledArc were reported by Bruce Verderaime. A simple and correct but inefficient implementation has been substituted until fixes are contributed for the faster code, which is in gd_arc_f_buggy.c along with the test program that reproduces the bug(s).
- gdImageFilledArc now offers additional style options, which can be combined to produce various effects.
- Masahito Yamaga (ma@yama-ga.com) sent a patch to improve support for Japanese output via gdImageStringFT. He also added a new `readme.jpn` file.
- Zillions of documentation fixes.

### What's new in version 2.0?

- Support for truecolor images! Version 2.0 can load truecolor PNGs with no loss of color information, and almost no loss of alpha channel information. Version 2.0 can also load truecolor JPEGs with as little loss as possible; however, bear in mind that JPEG is a lossy format, so repeated load/save cycles always reduce image quality. This is not a bug. To create a truecolor image from scratch, call the new gdImageCreateTrueColor function. The gdImageCreate function is still available to create palette images, and may also be referred to as gdImageCreatePalette.
- Support for alpha channels! In addition to 24 bits of color information for each pixel (eight bits of red, green, and blue respectively), version 2.0 supports 7 bits of "alpha channel" information. This is used to determine exactly how transparent the pixel should be. There is also support for a full 7 bits of transparency for each individual palette index in a palette-based image. Please note that, as of this writing, only Macintosh Internet Explorer 5.x and Mozilla/Netscape 6.x display partial transparency properly.
- The new gdImageAlphaBlending function allows for two different modes of drawing. In blending mode, the alpha channel component of the color supplied to all drawing functions, such as gdImageSetPixel, determines how much of the underlying color should be allowed to shine through. The resulting image is not transparent. In non-blending mode, drawing color is copied literally with the alpha channel information, resulting in a transparent image. Blending mode is not available when drawing on palette images.
- The gdImageCopyResampled function provides "smooth" copying from a large image to a smaller one, using a weighted average of the pixels of the source area rather than selecting one representative pixel. This function is identical to gdImageCopyResized when the destination image is a palette image.
- The gdImageTrueColorToPalette function converts a truecolor image to a palette image. The code for this function was originally drawn from the Independent JPEG Group library code, which is excellent. The code has been modified to preserve as much alpha channel information as possible in the resulting palette, in addition to preserving colors as well as possible. This does not work as well as might be hoped. It is usually best to simply produce a truecolor output image instead, which guarantees the highest output quality.
- A very high degree of backwards compatibility with existing gd 1.x code has been maintained, at both the source code and binary level. Code which directly accesses the `pixels` array will fail only if it encounters an existing truecolor image, which may happen if the code attempts to open and modify an existing JPEG or truecolor PNG. Such code should be modified to check the `trueColor` flag of the `gdImage` structure, and refer to the `tpixels` array instead when it is set.
- gd is now compiled and installed as a shared library. However, gd still does not use autoconf, because I (TBB) have very limited patience with autoconf. These days, most Unix systems provide a fairly POSIX-standard environment, and the provided Makefile is likely to work well if users read it and follow the instructions at the top.
- Support for line thickness was added by Michael Schwartz. My apologies to him for sitting on his patches for so long. See the new gdImageSetThickness function, which affects all standard gd functions that draw lines and curves. In addition, Michael added a convenient gdImageEllipse function.
- The new gdImageFilledArc function provides a straightforward way to draw filled arcs. Also, gdImageFilledEllipse is a convenient way to fill an ellipse without specifying starting and ending angles. Thanks go out to F J Franklin.
- To put an end to the confusion, TrueType 1.x support has been removed in favor of TrueType 2.x support. The old gdImageStringTTF function simply invokes gdImageStringFT.
- The specialized .gd and .gd2 file formats have been upgraded to support truecolor. New images written by the versions of these functions found in 2.0 will be rejected, with varying degrees of grace, by older versions of gd. THIS AFFECTS THE .GD and .GD2 FORMATS ONLY. IF YOU ARE CONFUSED BY THIS PARAGRAPH, IT PROBABLY DOESN'T APPLY TO ANYTHING YOU WILL EVER ENCOUNTER. Since these file formats are absolutely, positively *not* designed for distributing images, just for preprocessing them, this should not be a big problem. gd 2.0 should read old .gd and .gd2 files correctly.

### What's new in version 1.8.4?

- Add support for FreeType2 (John Ellson ellson@graphviz.org)
- Add support for finding in fonts in a builtin DEFAULT_FONTPATH, or in a path from the GDFONTPATH environment variable.
- remove some unused symbols to reduce compiler warnings
- bugfix in size comparisons in gdImageCompare
- REXX now mentioned
- All memory allocation functions are now wrapped within the library; gdFree is exported and recommended for freeing memory returned by the gdImage(Something)Ptr family of functions.

### What's new in version 1.8.3?

- WBMP output memory leak fixed
- `#include <gd.h>` corrected to `#include "gd.h"` in gd_wbmp.c
- Documented the fact that the source and output images shouldn't match in the WBMP test except for black and white source images

### What's new in version 1.8.2?

- WBMP support debugged and improved by Johann Van den Brande
- WBMP tests added to gdtest.c by Thomas Boutell
- Use of platform-dependent 'install' command removed by Thomas Boutell
- Comments added to Makefile warning users to juggle the order of the libraries if the linker complains; is there any portable way to do this automatically, short of using autoconf?
- Documentation of gdImageCreateFromXpm corrected
- Updated links to fast-moving, always dodging libpng and zlib web sites

### What's new in version 1.8.1?

- Optional components no longer built by default (following the documentation)
- JPEG code no longer requires inappropriate header files
- Win32 patches from Joe Gregorio
- 16-bit font support for bdftogd, from Honza Pazdziora

### What's new in version 1.8?

- Support for JPEG output, courtesy of Doug Becker
- A link to Michael Bradbery's Pascal wrapper
- Support for WBMP output, courtesy of Maurice Szmurlo
- gdImageColorClosestHWB function based on hue, whiteness, blackness, superior to the regular gdImageColorClosest function, courtesy of Philip Warner
- License clarification: yes, you can modify gd

#### Additional JPEG Information

Support for reading and writing JPEG-format images is courtesy of Doug Becker and the Independent JPEG Group / Thomas G. Lane. You can get the latest version of the IJG JPEG software from ftp://ftp.uu.net/graphics/jpeg/ (e.g., the jpegsrc.v6b.tar.gz file). You must use version 6b or later of the IJG JPEG software. You might also consult the JPEG FAQ at http://www.faqs.org/faqs/jpeg-faq/.

### What's new in version 1.7.3?

Another attempt at Makefile fixes to permit linking with all libraries required on platforms with order- dependent linkers. Perhaps it will work this time.

### What's new in version 1.7.2?

An uninitialized-pointer bug in `gdtestttf.c` was corrected. This bug caused crashes at the end of each call to gdImageStringTTF on some platforms. Thanks to Wolfgang Haefelinger.

Documentation fixes. Thanks to Dohn Arms.

Makefile fixes to permit linking with all libraries required on platforms with order- dependent linkers.

### What's new in version 1.7.1?

A minor buglet in the Makefile was corrected, as well as an inaccurate error message in `gdtestttf.c`. Thanks to Masahito Yamaga.

### What's new in version 1.7?

Version 1.7 contains the following changes:

- Japanese language support for the TrueType functions. Thanks to Masahito Yamaga.
- `autoconf` and `configure` have been removed, in favor of a carefully designed Makefile which produces and properly installs the library and the binaries. System-dependent variables are at the top of the Makefile for easy modification. I'm sorry, folks, but autoconf generated many, many confused email messages from people who didn't have things where autoconf expected to find them. I am not an autoconf/automake wizard, and gd is a simple, very compact library which does not need to be a shared library. I did make many improvements over the old gd 1.3 Makefile, which were directly inspired by the autoconf version found in the 1.6 series (thanks to John Ellson).
- Completely ANSI C compliant, according to the `-pedantic-errors` flag of gcc. Several pieces of not-quite-ANSI-C code were causing problems for those with non-gcc compilers.
- `gdttf.c` patched to allow the use of Windows symbol fonts, when present (thanks to Joseph Peppin).
- `extern "C"` wrappers added to `gd.h` and the font header files for the convenience of C++ programmers. `bdftogd` was also modified to automatically insert these wrappers into future font header files. Thanks to John Lindal.
- Compiles correctly on platforms that don't define `SEEK_SET`. Thanks to Robert Bonomi.
- Loads Xpm images via the `gdImageCreateFromXpm` function, if the Xpm library is available. Thanks to Caolan McNamara.

### What's new in version 1.6.3?

Version 1.6.3 corrects a memory leak in gd_png.c. This leak caused a significant amount of memory to be allocated and not freed when writing a PNG image.

### What's new in version 1.6.2?

Version 1.6.2 from John Ellson <ellson@graphviz.org> adds two new functions:

- gdImageStringTTF - scalable, rotatable, anti-aliased, TrueType strings using the FreeType library, but only if libttf is found by configure. We do not provide TrueType fonts. Obtaining them is entirely up to you.
- gdImageColorResolve - an efficient alternative for the common code fragment:

            if ((color=gdImageColorExact(im,R,G,B)) < 0)
                if ((color=gdImageColorAllocate(im,R,G,B)) < 0)
                    color=gdImageColorClosest(im,R,G,B);

Also in this release the build process has been converted to GNU autoconf/automake/libtool conventions so that both (or either) static and shared libraries can be built.

### What's new in version 1.6.1?

Version 1.6.1 incorporates superior PNG reading and writing code from Greg Roelofs, with minor modifications by Tom Boutell. Specifically, I altered his code to read non-palette images (converting them to palette images badly, by dithering them), and to tolerate palette images with types of transparency that gd doesn't actually support (it just ignores the advanced transparency features). Any bugs in this area are therefore my fault, not Greg's.

Unlike gd 1.6, users should have no trouble linking with gd 1.6.1 if they follow the instructions and install all of the pieces. However, If you get undefined symbol errors, be sure to check for older versions of libpng in your library directories!

### What's new in version 1.6?

Version 1.6 features the following changes:

Support for 8-bit palette PNG images has been added. Support for GIF has been removed. This step was taken to completely avoid the legal controversy regarding the LZW compression algorithm used in GIF. Unisys holds a patent which is relevant to LZW compression. PNG is a superior image format in any case. Now that PNG is supported by both Microsoft Internet Explorer and Netscape (in their recent releases), we highly recommend that GD users upgrade in order to get well-compressed images in a format which is legally unemcumbered.

### What's new in version 1.5?

Version 1.5 featured the following changes:

New GD2 format
  An improvement over the GD format, the GD2 format uses the zlib compression library to compress the image in chunks. This results in file sizes comparable to GIFs, with the ability to access parts of large images without having to read the entire image into memory.

  This format also supports version numbers and rudimentary validity checks, so it should be more 'supportable' than the previous GD format.

Re-arranged source files
  gd.c has been broken into constituant parts: io, gif, gd, gd2 and graphics functions are now in separate files.

Extended I/O capabilities.
  The source/sink feature has been extended to support GD2 file formats (which require seek/tell functions), and to allow more general non-file I/O.

Better support for Lincoln Stein's Perl Module
  The new gdImage*Ptr function returns the chosen format stored in a block of memory. This can be directly used by the GD perl module.

Added functions
  gdImageCreateFromGd2Part - allows retrieval of part of an image (good for huge images, like maps),
  gdImagePaletteCopy - Copies a palette from one image to another, doing it's best to match the colors in the target image to the colors in the source palette.
  gdImageGd2, gdImageCreateFromGd2 - Support for new format
  gdImageCopyMerge - Merges two images (useful to highlight part of an image)
  gdImageCopyMergeGray - Similar to gdImageCopyMerge, but tries to preserve source image hue.
  gdImagePngPtr, gdImageJpegPtr, gdImageWBMPPtr, gdImageGdPtr, gdImageGd2Ptr - return memory blocks for each type of image.
  gdImageCreateFromPngCtx, gdImageCreateFromGdCtx, gdImageCreateFromGd2Ctx, gdImageCreateFromGd2PartCtx - Support for new I/O context.

NOTE: In fairness to Thomas Boutell, any bug/problems with any of the above features should probably be reported to Philip Warner.

### What's new in version 1.4?

Version 1.4 features the following changes:

Fixed polygon fill routine (again)
  Thanks to Kirsten Schulz, version 1.4 is able to fill numerous types of polygons that caused problems with previous releases, including version 1.3.
Support for alternate data sources
  Programmers who wish to load a GIF from something other than a stdio FILE * stream can use the new gdImageCreateFromPngSource function.
Support for alternate data destinations
  Programmers who wish to write a GIF to something other than a stdio FILE * stream can use the new gdImagePngToSink function.
More tolerant when reading GIFs
  Version 1.4 does not crash when reading certain animated GIFs, although it still only reads the first frame. Version 1.4 also has overflow testing code to prevent crashes when reading damaged GIFs.

### What's new in version 1.3?

Version 1.3 features the following changes:

Non-LZW-based GIF compression code
  Version 1.3 contained GIF compression code that uses simple Run Length Encoding instead of LZW compression, while still retaining compatibility with normal LZW-based GIF decoders (your browser will still like your GIFs). LZW compression is patented by Unisys. We are currently reevaluating the approach taken by gd 1.3. The current release of gd does not support this approach. We recommend that you use the current release, and generate PNG images. Thanks to Hutchison Avenue Software Corporation for contributing the RLE GIF code.
8-bit fonts, and 8-bit font support
  This improves support for European languages. Thanks are due to Honza Pazdziora <adelton@informatics.muni.cz> and also to Jan Pazdziora <adelton@fi.muni.cz>. Also see the provided bdftogd Perl script if you wish to convert fixed-width X11 fonts to gd fonts.
16-bit font support (no fonts provided)
  Although no such fonts are provided in the distribution, fonts containing more than 256 characters should work if the gdImageString16 and gdImageStringUp16 routines are used.
Improvements to the "webpng" example/utility
  The "webpng" utility is now a slightly more useful application. Thanks to Brian Dowling for this code.
Corrections to the color resolution field of GIF output
  Thanks to Bruno Aureli.
Fixed polygon fills
  A one-line patch for the infamous polygon fill bug, courtesy of Jim Mason. I believe this fix is sufficient. However, if you find a situation where polygon fills still fail to behave properly, please send code that demonstrates the problem, and a fix if you have one. Verifying the fix is important.
Row-major, not column-major
  Internally, gd now represents the array of pixels as an array of rows of pixels, rather than an array of columns of pixels. This improves the performance of compression and decompression routines slightly, because horizontally adjacent pixels are now next to each other in memory. This should not affect properly written gd applications, but applications that directly manipulate the `pixels` array will require changes.

### What else do I need to use gd?

To use gd, you will need an ANSI C compiler. All popular Windows 95 and NT C compilers are ANSI C compliant. Any full-ANSI-standard C compiler should be adequate. The cc compiler released with SunOS 4.1.3 is not an ANSI C compiler. Most Unix users who do not already have gcc should get it. gcc is free, ANSI compliant and a de facto industry standard. Ask your ISP why it is missing.

As of version 1.6, you also need the zlib compression library, and the libpng library. As of version 1.6.2, you can draw text using antialiased TrueType fonts if you also have the libttf library installed, but this is not mandatory. zlib is available for a variety of platforms from the zlib web site. libpng is available for a variety of platforms from the PNG web site.

You will also want a PNG viewer, if you do not already have one for your system, since you will need a good way to check the results of your work. Netscape 4.04 and higher, and Microsoft Internet Explorer 4.0 or higher, both support PNG. For some purposes you might be happier with a package like Lview Pro for Windows or xv for X. There are PNG viewers available for every graphics-capable modern operating system, so consult newsgroups relevant to your particular system.

### How do I get gd?

#### By HTTP

- Gzipped Tar File (Unix)
- .ZIP File (Windows)

#### By FTP

- Gzipped Tar File (Unix)
- .ZIP File (Windows)

### How do I build gd?

In order to build gd, you must first unpack the archive you have downloaded. If you are not familiar with `tar` and `gunzip` (Unix) or `ZIP` (Windows), please consult with an experienced user of your system. Sorry, we cannot answer questions about basic Internet skills.

Unpacking the archive will produce a directory called "gd-2.0.1".

#### For Unix

`cd` to the 2.0.1 directory. Edit the Makefile with your preferred text editor and make any necessary changes to the settings at the top, especially if you want Xpm or TrueType support. Next, type "make install". Because gd 2.0 and above installs as a shared library, it is necessary to install the library properly before running gd-based programs.

If you get errors, edit the Makefile again, paying special attention to the INCLUDEDIRS and LIBDIRS settings.

IF YOU GET LINKER ERRORS, TRY JUGGLING THE ORDER OF THE -l DIRECTIVES IN THE MAKEFILE. Some platforms may prefer that the libraries be listed in the opposite order.

#### For Windows, Mac, Et Cetera

Create a project using your favorite programming environment. Copy all of the gd files to the project directory. Add `gd.c` to your project. Add other source files as appropriate. Learning the basic skills of creating projects with your chosen C environment is up to you.

If you wish to test the library, type "make test" AFTER you have successfully executed "make install". This will build several test programs, including "gddemo". Run gddemo to see some of the capabilities of gd.

gddemo should execute without incident, creating the file demoout.png. (Note there is also a file named demoin.png, which is provided in the package as part of the demonstration.)

Display demoout.png in your PNG viewer. The image should be 128x128 pixels and should contain an image of the space shuttle with quite a lot of graphical elements drawn on top of it.

(If you are missing the demoin.png file, the other items should appear anyway.)

Look at demoin.png to see the original space shuttle image which was scaled and copied into the output image.

### gd basics: using gd in your program

gd lets you create PNG or JPEG images on the fly. To use gd in your program, include the file gd.h, and link with the libgd.a library produced by "make libgd.a", under Unix. Under other operating systems you will add gd.c to your own project.

If you want to use the provided fonts, include gdfontt.h, gdfonts.h, gdfontmb.h, gdfontl.h and/or gdfontg.h. For more impressive results, install FreeType 2.x and use the new gdImageStringFT function. If you are not using the provided Makefile and/or a library-based approach, be sure to include the source modules as well in your project. (They may be too large for 16-bit memory models, that is, 16-bit DOS and Windows.)

Here is a short example program. (For a more advanced example, see gddemo.c, included in the distribution. gddemo.c is NOT the same program; it demonstrates additional features!)

    /* Bring in gd library functions */
    #include "gd.h"

    /* Bring in standard I/O so we can output the PNG to a file */
    #include <stdio.h>

    int main() {
    	/* Declare the image */
    	gdImagePtr im;
    	/* Declare output files */
    	FILE *pngout, *jpegout;
    	/* Declare color indexes */
    	int black;
    	int white;

    	/* Allocate the image: 64 pixels across by 64 pixels tall */
    	im = gdImageCreate(64, 64);

    	/* Allocate the color black (red, green and blue all minimum).
    		Since this is the first color in a new image, it will
    		be the background color. */
    	black = gdImageColorAllocate(im, 0, 0, 0);

    	/* Allocate the color white (red, green and blue all maximum). */
    	white = gdImageColorAllocate(im, 255, 255, 255);

    	/* Draw a line from the upper left to the lower right,
    		using white color index. */
    	gdImageLine(im, 0, 0, 63, 63, white);

    	/* Open a file for writing. "wb" means "write binary", important
    		under MSDOS, harmless under Unix. */
    	pngout = fopen("test.png", "wb");

    	/* Do the same for a JPEG-format file. */
    	jpegout = fopen("test.jpg", "wb");

    	/* Output the image to the disk file in PNG format. */
    	gdImagePng(im, pngout);

    	/* Output the same image in JPEG format, using the default
    		JPEG quality setting. */
    	gdImageJpeg(im, jpegout, -1);

    	/* Close the files. */
    	fclose(pngout);
    	fclose(jpegout);

    	/* Destroy the image in memory. */
    	gdImageDestroy(im);
    }

When executed, this program creates an image, allocates two colors (the first color allocated becomes the background color), draws a diagonal line (note that 0, 0 is the upper left corner), writes the image to PNG and JPEG files, and destroys the image.

The above example program should give you an idea of how the package works. gd provides many additional functions, which are listed in the following reference chapters, complete with code snippets demonstrating each. There is also an alphabetical index.

### Webpng: a more powerful gd example

Webpng is a simple utility program to manipulate PNGs from the command line. It is written for Unix and similar command-line systems, but should be easily adapted for other environments. Webpng allows you to set transparency and interlacing and output interesting information about the PNG in question.

webpng.c is provided in the distribution. Unix users can simply type "make webpng" to compile the program. Type "webpng" with no arguments to see the available options.

## Function and type reference

- Types
- Image creation, destruction, loading and saving
- Drawing, styling, brushing, tiling and filling functions
- Query functions (not color-related)
- Font and text-handling functions
- Color handling functions
- Copying and resizing functions
- Miscellaneous Functions
- Constants

### Types

`gdImage`(TYPE)
  The data structure in which gd stores images. gdImageCreate, gdImageCreateTrueColor and the various image file-loading functions return a pointer to this type, and the other functions expect to receive a pointer to this type as their first argument. It is reasonably safe to examine any of the members of this structure. It is also reasonably safe to modify individual pixels within the `pixels` or `tpixels` arrays. If the `trueColor` flag is set, the `tpixels` array is valid; otherwise the `pixels` array is valid.

  The `colorsTotal`, `red`, `green`, `blue`, `alpha` and `open` arrays manage the palette. They are valid only when the `trueColor` flag is not set. The `transparent` value contains the palette index of the first transparent color as read-only information for backwards compatibility; gd 2.0 stores this information in the `alpha` array so that variable transparency can be supported for each palette entry. However, for truecolor images, `transparent` represents a single RGB color which is always 100% transparent, and this feature is generally supported by browsers which do not support full alpha channels.

      typedef struct {
      	/* Palette-based image pixels */
      	unsigned char ** pixels;
      	int sx;
      	int sy;
      	/* These are valid in palette images only. See also
      	/* 'alpha', which appears later in the structure to
      		preserve binary backwards compatibility */
      	int colorsTotal;
      	int red[gdMaxColors];
      	int green[gdMaxColors];
      	int blue[gdMaxColors];
      	int open[gdMaxColors];
      	/* For backwards compatibility, this is set to the
      		first palette entry with 100% transparency,
      		and is also set and reset by the
      		gdImageColorTransparent function. Newer
      		applications can allocate palette entries
      		with any desired level of transparency; however,
      		bear in mind that many viewers, notably
      		many web browsers, fail to implement
      		full alpha channel for PNG and provide
      		support for full opacity or transparency only. */
      	int transparent;
      	int *polyInts;
      	int polyAllocated;
      	struct gdImageStruct *brush;
      	struct gdImageStruct *tile;
      	int brushColorMap[gdMaxColors];
      	int tileColorMap[gdMaxColors];
      	int styleLength;
      	int stylePos;
      	int *style;
      	int interlace;
      	/* New in 2.0: alpha channel for palettes. Note that only
      		Macintosh Internet Explorer and (possibly) Netscape 6
      		really support multiple levels of transparency in
      		palettes, to my knowledge, as of 2/15/01. Most
      		common browsers will display 100% opaque and
      		100% transparent correctly, and do something
      		unpredictable and/or undesirable for levels
      		in between. TBB */
      	int alpha[gdMaxColors];
      	/* Truecolor flag and pixels. New 2.0 fields appear here at the
      		end to minimize breakage of existing object code. */
      	int trueColor;
      	int ** tpixels;
      	/* Should alpha channel be copied, or applied, each time a
      		pixel is drawn? This applies to truecolor images only.
      		No attempt is made to alpha-blend in palette images,
      		even if semitransparent palette entries exist.
      		To do that, build your image as a truecolor image,
      		then quantize down to 8 bits. */
      	int alphaBlendingFlag;
      	/* Should the alpha channel of the image be saved? This affects
      		PNG at the moment; other future formats may also
      		have that capability. JPEG doesn't. */
      	int saveAlphaFlag;
      } gdImage;

  The order of the structure members may appear confusing, but was chosen deliberately to increase backwards compatibility with existing gd 1.x-based binary code that references particular structure members.

gdImagePtr (TYPE)
  A pointer to an image structure. gdImageCreate returns this type, and the other functions expect it as the first argument.
gdFont (TYPE)
  A font structure. Used to declare the characteristics of a font. Plese see the files gdfontl.c and gdfontl.h for an example of the proper declaration of this structure. You can provide your own font data by providing such a structure and the associated pixel array. You can determine the width and height of a single character in a font by examining the w and h members of the structure. If you will not be creating your own fonts, you will not need to concern yourself with the rest of the components of this structure.

      typedef struct {
      	/* # of characters in font */
      	int nchars;
      	/* First character is numbered... (usually 32 = space) */
      	int offset;
      	/* Character width and height */
      	int w;
      	int h;
      	/* Font data; array of characters, one row after another.
      		Easily included in code, also easily loaded from
      		data files. */
      	char *data;
      } gdFont;

gdFontPtr (TYPE)
  A pointer to a font structure. Text-output functions expect these as their second argument, following the gdImagePtr argument. Two such pointers are declared in the provided include files gdfonts.h and gdfontl.h.
gdPoint (TYPE)
  Represents a point in the coordinate space of the image; used by gdImagePolygon and gdImageFilledPolygon.

      typedef struct {
              int x, y;
      } gdPoint, *gdPointPtr;

gdPointPtr (TYPE)
  A pointer to a gdPoint structure; passed as an argument to gdImagePolygon and gdImageFilledPolygon.

gdSource (TYPE)

      typedef struct {
              int (*source) (void *context, char *buffer, int len);
              void *context;
      } gdSource, *gdSourcePtr;

  Represents a source from which a PNG can be read. Programmers who do not wish to read PNGs from a file can provide their own alternate input mechanism, using the gdImageCreateFromPngSource function. See the documentation of that function for an example of the proper use of this type.
gdSink (TYPE)

      typedef struct {
              int (*sink) (void *context, char *buffer, int len);
              void *context;
      } gdSink, *gdSinkPtr;

  Represents a "sink" (destination) to which a PNG can be written. Programmers who do not wish to write PNGs to a file can provide their own alternate output mechanism, using the gdImagePngToSink function. See the documentation of that function for an example of the proper use of this type.

  ### Image creation, destruction, loading and saving

  gdImageCreate(sx, sy) (FUNCTION)
    gdImageCreate is called to create palette-based images, with no more than 256 colors. Invoke gdImageCreate with the x and y dimensions of the desired image. gdImageCreate returns a gdImagePtr to the new image, or NULL if unable to allocate the image. The image must eventually be destroyed using gdImageDestroy().

        ... inside a function ...
        gdImagePtr im;
        im = gdImageCreate(64, 64);
        /* ... Use the image ... */
        gdImageDestroy(im);

  gdImageCreateTrueColor(sx, sy) (FUNCTION)
    gdImageCreateTrueColor is called to create truecolor images, with an essentially unlimited number of colors. Invoke gdImageCreateTrueColor with the x and y dimensions of the desired image. gdImageCreateTrueColor returns a gdImagePtr to the new image, or NULL if unable to allocate the image. The image must eventually be destroyed using gdImageDestroy().

    Truecolor images are always filled with black at creation time.

        ... inside a function ...
        gdImagePtr im;
        im = gdImageCreateTrueColor(64, 64);
        /* ... Use the image ... */
        gdImageDestroy(im);

  gdImageCreateFromJpeg(FILE *in) (FUNCTION)
  gdImageCreateFromJpegCtx(FILE *in) (FUNCTION)

  gdImageCreateFromJpeg(FILE *in) (FUNCTION)
  gdImageCreateFromJpegCtx(FILE *in) (FUNCTION)

    gdImageCreateFromJpeg is called to load images from JPEG format files. Invoke gdImageCreateFromJpeg with an already opened pointer to a file containing the desired image. gdImageCreateFromJpeg returns a gdImagePtr to the new truecolor image, or NULL if unable to load the image (most often because the file is corrupt or does not contain a JPEG image). gdImageCreateFromJpeg does not close the file. You can inspect the sx and sy members of the image to determine its size. The image must eventually be destroyed using gdImageDestroy(). The returned image is always a truecolor image.

        gdImagePtr im;
        ... inside a function ...
        FILE *in;
        in = fopen("myjpeg.jpg", "rb");
        im = gdImageCreateFromJpeg(in);
        fclose(in);
        /* ... Use the image ... */
        gdImageDestroy(im);

  gdImageCreateFromPng(FILE *in) (FUNCTION)
  gdImageCreateFromPngCtx(gdIOCtx *in) (FUNCTION)

    gdImageCreateFromPng is called to load images from PNG format files. Invoke gdImageCreateFromPng with an already opened pointer to a file containing the desired image. gdImageCreateFromPng returns a gdImagePtr to the new image, or NULL if unable to load the image (most often because the file is corrupt or does not contain a PNG image). gdImageCreateFromPng does not close the file. You can inspect the sx and sy members of the image to determine its size. The image must eventually be destroyed using gdImageDestroy().

    If the PNG image being loaded is a truecolor image, the resulting gdImagePtr will refer to a truecolor image. If the PNG image being loaded is a palette or grayscale image, the resulting gdImagePtr will refer to a palette image. gd retains only 8 bits of resolution for each of the red, green and blue channels, and only 7 bits of resolution for the alpha channel. The former restriction affects only a handful of very rare 48-bit color and 16-bit grayscale PNG images. The second restriction affects all semitransparent PNG images, but the difference is essentially invisible to the eye. 7 bits of alpha channel resolution is, in practice, quite a lot.

        gdImagePtr im;
        ... inside a function ...
        FILE *in;
        in = fopen("mypng.png", "rb");
        im = gdImageCreateFromPng(in);
        fclose(in);
        /* ... Use the image ... */
        gdImageDestroy(im);

  gdImageCreateFromPngSource(gdSourcePtr in) (FUNCTION)
    gdImageCreateFromPngSource is called to load a PNG from a data source other than a file. Usage is very similar to the gdImageCreateFromPng function, except that the programmer provides a custom data source.

    The programmer must write an input function which accepts a context pointer, a buffer, and a number of bytes to be read as arguments. This function must read the number of bytes requested, unless the end of the file has been reached, in which case the function should return zero, or an error has occurred, in which case the function should return `-1`. The programmer then creates a gdSource structure and sets the `source` pointer to the input function and the context pointer to any value which is useful to the programmer.

    The example below implements gdImageCreateFromPng by creating a custom data source and invoking gdImageCreateFromPngSource.

        static int freadWrapper(void *context, char *buf, int len);

        gdImagePtr gdImageCreateFromPng(FILE *in)
        {
                gdSource s;
                s.source = freadWrapper;
                s.context = in;
                return gdImageCreateFromPngSource(&s);
        }

        static int freadWrapper(void *context, char *buf, int len)
        {
                int got = fread(buf, 1, len, (FILE *) context);
                return got;
        }

  gdImageCreateFromGd(FILE *in) (FUNCTION)
  gdImageCreateFromGdCtx(gdIOCtx *in) (FUNCTION)

    gdImageCreateFromGd is called to load images from gd format files. Invoke gdImageCreateFromGd with an already opened pointer to a file containing the desired image in the gd file format, which is specific to gd and intended for very fast loading. (It is not intended for compression; for compression, use PNG or JPEG.) gdImageCreateFromGd returns a gdImagePtr to the new image, or NULL if unable to load the image (most often because the file is corrupt or does not contain a gd format image). gdImageCreateFromGd does not close the file. You can inspect the sx and sy members of the image to determine its size. The image must eventually be destroyed using gdImageDestroy().

        ... inside a function ...
        gdImagePtr im;
        FILE *in;
        in = fopen("mygd.gd", "rb");
        im = gdImageCreateFromGd(in);
        fclose(in);
        /* ... Use the image ... */
        gdImageDestroy(im);

  gdImageCreateFromGd2(FILE *in) (FUNCTION)
  gdImageCreateFromGd2Ctx(gdIOCtx *in) (FUNCTION)

    gdImageCreateFromGd2 is called to load images from gd2 format files. Invoke gdImageCreateFromGd2 with an already opened pointer to a file containing the desired image in the gd2 file format, which is specific to gd2 and intended for fast loading of parts of large images. (It is a compressed format, but generally not as good as maximum compression of the entire image would be.) gdImageCreateFromGd returns a gdImagePtr to the new image, or NULL if unable to load the image (most often because the file is corrupt or does not contain a gd format image). gdImageCreateFromGd2 does not close the file. You can inspect the sx and sy members of the image to determine its size. The image must eventually be destroyed using gdImageDestroy().

        ... inside a function ...
        gdImagePtr im;
        FILE *in;
        in = fopen("mygd.gd2", "rb");
        im = gdImageCreateFromGd2(in);
        fclose(in);
        /* ... Use the image ... */
        gdImageDestroy(im);

  gdImageCreateFromGd2Part(FILE *in, int srcX, int srcY, int w, int h) (FUNCTION)
  gdImageCreateFromGd2PartCtx(gdIOCtx *in) (FUNCTION)

    gdImageCreateFromGd2Part is called to load parts of images from gd2 format files. Invoked in the same way as gdImageCreateFromGd2, but with extra parameters indicating the source (x, y) and width/height of the desired image. gdImageCreateFromGd2Part returns a gdImagePtr to the new image, or NULL if unable to load the image. The image must eventually be destroyed using gdImageDestroy().

  gdImageCreateFromXbm(FILE *in) (FUNCTION)
    gdImageCreateFromXbm is called to load images from X bitmap format files. Invoke gdImageCreateFromXbm with an already opened pointer to a file containing the desired image. gdImageCreateFromXbm returns a gdImagePtr to the new image, or NULL if unable to load the image (most often because the file is corrupt or does not contain an X bitmap format image). gdImageCreateFromXbm does not close the file. You can inspect the sx and sy members of the image to determine its size. The image must eventually be destroyed using gdImageDestroy().

        ... inside a function ...
        gdImagePtr im;
        FILE *in;
        in = fopen("myxbm.xbm", "rb");
        im = gdImageCreateFromXbm(in);
        fclose(in);
        /* ... Use the image ... */
        gdImageDestroy(im);

  gdImageCreateFromXpm(char *filename) (FUNCTION)
    gdImageCreateFromXbm is called to load images from XPM X Window System color bitmap format files. This function is available only if HAVE_XPM is selected in the Makefile and the Xpm library is linked with the application. Unlike most gd file functions, the Xpm functions require filenames, not file pointers. gdImageCreateFromXpm returns a gdImagePtr to the new image, or NULL if unable to load the image (most often because the file is corrupt or does not contain an XPM bitmap format image). You can inspect the sx and sy members of the image to determine its size. The image must eventually be destroyed using gdImageDestroy().

        ... inside a function ...
        gdImagePtr im;
        FILE *in;
        in = fopen("myxpm.xpm", "rb");
        im = gdImageCreateFromXpm(in);
        fclose(in);
        /* ... Use the image ... */
        gdImageDestroy(im);

  gdImageDestroy(gdImagePtr im) (FUNCTION)
    gdImageDestroy is used to free the memory associated with an image. It is important to invoke gdImageDestroy before exiting your program or assigning a new image to a gdImagePtr variable.

        ... inside a function ...
        gdImagePtr im;
        im = gdImageCreate(10, 10);
        /* ... Use the image ... */
        /* Now destroy it */
        gdImageDestroy(im);

  void gdImageJpeg(gdImagePtr im, FILE *out, int quality) (FUNCTION)
  void gdImageJpegCtx(gdImagePtr im, gdIOCtx *out, int quality) (FUNCTION)
    gdImageJpeg outputs the specified image to the specified file in JPEG format. The file must be open for writing. Under MSDOS and all versions of Windows, it is important to use "wb" as opposed to simply "w" as the mode when opening the file, and under Unix there is no penalty for doing so. gdImageJpeg does not close the file; your code must do so.

    If quality is negative, the default IJG JPEG quality value (which should yield a good general quality / size tradeoff for most situations) is used. Otherwise, for practical purposes, quality should be a value in the range 0-95, higher quality values usually implying both higher quality and larger image sizes.

    If you have set image interlacing using gdImageInterlace, this function will interpret that to mean you wish to output a progressive JPEG. Some programs (e.g., Web browsers) can display progressive JPEGs incrementally; this can be useful when browsing over a relatively slow communications link, for example. Progressive JPEGs can also be slightly smaller than sequential (non-progressive) JPEGs.

        ... inside a function ...
        gdImagePtr im;
        int black, white;
        FILE *out;
        /* Create the image */
        im = gdImageCreate(100, 100);
        /* Allocate background */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Allocate drawing color */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Draw rectangle */
        gdImageRectangle(im, 0, 0, 99, 99, black);
        /* Open output file in binary mode */
        out = fopen("rect.jpg", "wb");
        /* Write JPEG using default quality */
        gdImageJpeg(im, out, -1);
        /* Close file */
        fclose(out);
        /* Destroy image */
        gdImageDestroy(im);

  void* gdImageJpegPtr(gdImagePtr im, int *size) (FUNCTION)
    Identical to gdImageJpeg except that it returns a pointer to a memory area with the JPEG data. This memory must be freed by the caller when it is no longer needed. The caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.
  void gdImagePng(gdImagePtr im, FILE *out) (FUNCTION)
    gdImagePng outputs the specified image to the specified file in PNG format. The file must be open for writing. Under MSDOS and all versions of Windows, it is important to use "wb" as opposed to simply "w" as the mode when opening the file, and under Unix there is no penalty for doing so. gdImagePng does not close the file; your code must do so.

        ... inside a function ...
        gdImagePtr im;
        int black, white;
        FILE *out;
        /* Create the image */
        im = gdImageCreate(100, 100);
        /* Allocate background */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Allocate drawing color */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Draw rectangle */
        gdImageRectangle(im, 0, 0, 99, 99, black);
        /* Open output file in binary mode */
        out = fopen("rect.png", "wb");
        /* Write PNG */
        gdImagePng(im, out);
        /* Close file */
        fclose(out);
        /* Destroy image */
        gdImageDestroy(im);

  void* gdImagePngPtr(gdImagePtr im, int *size) (FUNCTION)
    Identical to gdImagePng except that it returns a pointer to a memory area with the PNG data. This memory must be freed by the caller when it is no longer needed. The caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.
  gdImagePngToSink(gdImagePtr im, gdSinkPtr out) (FUNCTION)
    gdImagePngToSink is called to write a PNG to a data "sink" (destination) other than a file. Usage is very similar to the gdImagePng function, except that the programmer provides a custom data sink.

    The programmer must write an output function which accepts a context pointer, a buffer, and a number of bytes to be written as arguments. This function must write the number of bytes requested and return that number, unless an error has occurred, in which case the function should return `-1`. The programmer then creates a gdSink structure and sets the `sink` pointer to the output function and the context pointer to any value which is useful to the programmer.

    The example below implements gdImagePng by creating a custom data source and invoking gdImagePngFromSink.

        static int stdioSink(void *context, char *buffer, int len)
        {
        	return fwrite(buffer, 1, len, (FILE *) context);
        }

        void gdImagePng(gdImagePtr im, FILE *out)
        {
        	gdSink mySink;
        	mySink.context = (void *) out;
        	mySink.sink = stdioSink;
        	gdImagePngToSink(im, &mySink);
        }

  void gdImageWBMP(gdImagePtr im, int fg, FILE *out)
  gdImageWBMPCtx(gdIOCtx *out) (FUNCTION)(FUNCTION)
    gdImageWBMP outputs the specified image to the specified file in WBMP format. The file must be open for writing. Under MSDOS and all versions of Windows, it is important to use "wb" as opposed to simply "w" as the mode when opening the file, and under Unix there is no penalty for doing so. gdImageWBMP does not close the file; your code must do so.

    WBMP file support is black and white only. The color index specified by the fg argument is the "foreground," and only pixels of this color will be set in the WBMP file. All other pixels will be considered "background."

        ... inside a function ...
        gdImagePtr im;
        int black, white;
        FILE *out;
        /* Create the image */
        im = gdImageCreate(100, 100);
        /* Allocate background */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Allocate drawing color */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Draw rectangle */
        gdImageRectangle(im, 0, 0, 99, 99, black);
        /* Open output file in binary mode */
        out = fopen("rect.wbmp", "wb");
        /* Write WBMP, with black as foreground */
        gdImageWBMP(im, black, out);
        /* Close file */
        fclose(out);
        /* Destroy image */
        gdImageDestroy(im);

  void* gdImageWBMPPtr(gdImagePtr im, int *size) (FUNCTION)
    Identical to gdImageWBMP except that it returns a pointer to a memory area with the WBMP data. This memory must be freed by the caller when it is no longer needed. The caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.
  void gdImageGd(gdImagePtr im, FILE *out) (FUNCTION)
    gdImageGd outputs the specified image to the specified file in the gd image format. The file must be open for writing. Under MSDOS and all versions of Windows, it is important to use "wb" as opposed to simply "w" as the mode when opening the file, and under Unix there is no penalty for doing so. gdImagePng does not close the file; your code must do so.

    The gd image format is intended for fast reads and writes of images your program will need frequently to build other images. It is not a compressed format, and is not intended for general use.

        ... inside a function ...
        gdImagePtr im;
        int black, white;
        FILE *out;
        /* Create the image */
        im = gdImageCreate(100, 100);
        /* Allocate background */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Allocate drawing color */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Draw rectangle */
        gdImageRectangle(im, 0, 0, 99, 99, black);
        /* Open output file in binary mode */
        out = fopen("rect.gd", "wb");
        /* Write gd format file */
        gdImageGd(im, out);
        /* Close file */
        fclose(out);
        /* Destroy image */
        gdImageDestroy(im);

  void* gdImageGdPtr(gdImagePtr im, int *size) (FUNCTION)
    Identical to gdImageGd except that it returns a pointer to a memory area with the GD data. This memory must be freed by the caller when it is no longer needed. The caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.
  void gdImageGd2(gdImagePtr im, FILE *out, int chunkSize, int fmt) (FUNCTION)
    gdImageGd2 outputs the specified image to the specified file in the gd2 image format. The file must be open for writing. Under MSDOS and all versions of Windows, it is important to use "wb" as opposed to simply "w" as the mode when opening the file, and under Unix there is no penalty for doing so. gdImageGd2 does not close the file; your code must do so.

    The gd2 image format is intended for fast reads and writes of parts of images. It is a compressed format, and well suited to retrieving smll sections of much larger images. The third and fourth parameters are the 'chunk size' and format resposectively.

    The file is stored as a series of compressed subimages, and the Chunk Size determines the sub-image size - a value of zero causes the GD library to use the default.

    It is also possible to store GD2 files in an uncompressed format, in which case the fourth parameter should be GD2_FMT_RAW.

        ... inside a function ...
        gdImagePtr im;
        int black, white;
        FILE *out;
        /* Create the image */
        im = gdImageCreate(100, 100);
        /* Allocate background */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Allocate drawing color */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Draw rectangle */
        gdImageRectangle(im, 0, 0, 99, 99, black);
        /* Open output file in binary mode */
        out = fopen("rect.gd", "wb");
        /* Write gd2 format file */
        gdImageGd2(im, out, 0, GD2_FMT_COMPRESSED);
        /* Close file */
        fclose(out);
        /* Destroy image */
        gdImageDestroy(im);

  void* gdImageGd2Ptr(gdImagePtr im, int chunkSize, int fmt, int *size) (FUNCTION)
    Identical to gdImageGd2 except that it returns a pointer to a memory area with the GD2 data. This memory must be freed by the caller when it is no longer needed. The caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.

  ### Drawing Functions

  void gdImageSetPixel(gdImagePtr im, int x, int y, int color) (FUNCTION)
    gdImageSetPixel sets a pixel to a particular color index. Always use this function or one of the other drawing functions to access pixels; do not access the pixels of the gdImage structure directly.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Set a pixel near the center. */
        gdImageSetPixel(im, 50, 50, white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageLine(gdImagePtr im, int x1, int y1, int x2, int y2, int color) (FUNCTION)
    gdImageLine is used to draw a line between two endpoints (x1,y1 and x2, y2). The line is drawn using the color index specified. Note that the color index can be an actual color returned by gdImageColorAllocate or one of gdStyled, gdBrushed or gdStyledBrushed.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Draw a line from the upper left corner to the lower right corner. */
        gdImageLine(im, 0, 0, 99, 99, white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageDashedLine(gdImagePtr im, int x1, int y1, int x2, int y2, int color) (FUNCTION)
    gdImageDashedLine is provided solely for backwards compatibility with gd 1.0. New programs should draw dashed lines using the normal gdImageLine function and the new gdImageSetStyle function.

    gdImageDashedLine is used to draw a dashed line between two endpoints (x1,y1 and x2, y2). The line is drawn using the color index specified. The portions of the line that are not drawn are left transparent so the background is visible.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Draw a dashed line from the upper left corner to the lower right corner. */
        gdImageDashedLine(im, 0, 0, 99, 99);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImagePolygon(gdImagePtr im, gdPointPtr points, int pointsTotal, int color) (FUNCTION)
    gdImagePolygon is used to draw a polygon with the verticies (at least 3) specified, using the color index specified. See also gdImageFilledPolygon.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        /* Points of polygon */
        gdPoint points[3];
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Draw a triangle. */
        points[0].x = 50;
        points[0].y = 0;
        points[1].x = 99;
        points[1].y = 99;
        points[2].x = 0;
        points[2].y = 99;
        gdImagePolygon(im, points, 3, white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageRectangle(gdImagePtr im, int x1, int y1, int x2, int y2, int color) (FUNCTION)
    gdImageRectangle is used to draw a rectangle with the two corners (upper left first, then lower right) specified, using the color index specified.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Draw a rectangle occupying the central area. */
        gdImageRectangle(im, 25, 25, 74, 74, white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageFilledPolygon(gdImagePtr im, gdPointPtr points, int pointsTotal, int color) (FUNCTION)
    gdImageFilledPolygon is used to fill a polygon with the verticies (at least 3) specified, using the color index specified. See also gdImagePolygon.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        int red;
        /* Points of polygon */
        gdPoint points[3];
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Allocate the color red. */
        red = gdImageColorAllocate(im, 255, 0, 0);
        /* Draw a triangle. */
        points[0].x = 50;
        points[0].y = 0;
        points[1].x = 99;
        points[1].y = 99;
        points[2].x = 0;
        points[2].y = 99;
        /* Paint it in white */
        gdImageFilledPolygon(im, points, 3, white);
        /* Outline it in red; must be done second */
        gdImagePolygon(im, points, 3, red);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageFilledRectangle(gdImagePtr im, int x1, int y1, int x2, int y2, int color) (FUNCTION)
    gdImageFilledRectangle is used to draw a solid rectangle with the two corners (upper left first, then lower right) specified, using the color index specified.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = int gdImageColorAllocate(im, 255, 255, 255);
        /* Draw a filled rectangle occupying the central area. */
        gdImageFilledRectangle(im, 25, 25, 74, 74, white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageArc(gdImagePtr im, int cx, int cy, int w, int h, int s, int e, int color) (FUNCTION)
    gdImageArc is used to draw a partial ellipse centered at the given point, with the specified width and height in pixels. The arc begins at the position in degrees specified by `s` and ends at the position specified by `e`. The arc is drawn in the color specified by the last argument. A circle can be drawn by beginning from 0 degrees and ending at 360 degrees, with width and height being equal. e must be greater than s. Values greater than 360 are interpreted modulo 360.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 50);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Inscribe an ellipse in the image. */
        gdImageArc(im, 50, 25, 98, 48, 0, 360, white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageFilledArc(gdImagePtr im, int cx, int cy, int w, int h, int s, int e, int color, int style) (FUNCTION)
    gdImageFilledArc is used to draw a partial ellipse centered at the given point, with the specified width and height in pixels. The arc begins at the position in degrees specified by `s` and ends at the position specified by `e`. The arc is filled in the color specified by the second to last argument. A circle can be drawn by beginning from 0 degrees and ending at 360 degrees, with width and height being equal. e must be greater than s. Values greater than 360 are interpreted modulo 360. The last argument is a bitwise OR of the following possibilities:
    - gdArc
    - gdChord
    - gdPie (synonym for gdChord)
    - gdNoFill
    - gdEdged
    gdArc and gdChord are mutually exclusive; gdChord just connects the starting and ending angles with a straight line, while gdArc produces a rounded edge. gdPie is a synonym for gdArc. gdNoFill indicates that the arc or chord should be outlined, not filled. gdEdged, used together with gdNoFill, indicates that the beginning and ending angles should be connected to the center; this is a good way to outline (rather than fill) a 'pie slice'.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 50);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Inscribe a filled pie slice in the image. */
        gdImageFilledArc(im, 50, 25, 98, 48, 0, 45, white, gdArc);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageFilledEllipse(gdImagePtr im, int cx, int cy, int w, int h, int s, int e, int color) (FUNCTION)
    gdImageFilledEllipse is used to draw an ellipse centered at the given point, with the specified width and height in pixels. The ellipse is filled in the color specified by the last argument. A circle can be drawn by beginning from 0 degrees and ending at 360 degrees, with width and height being equal. e must be greater than s. Values greater than 360 are interpreted modulo 360.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 50);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Inscribe a filled ellipse in the image. */
        gdImageFilledEllipse(im, 50, 25, 98, 48, white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageFillToBorder(gdImagePtr im, int x, int y, int border, int color) (FUNCTION)
    gdImageFillToBorder floods a portion of the image with the specified `color`, beginning at the specified point and stopping at the specified `border` color. For a way of flooding an area defined by the color of the starting point, see gdImageFill.

    The border color cannot be a special color such as gdTiled; it must be a proper solid color. The fill color can be, however.

    Note that gdImageFillToBorder is recursive. It is not the most naive implementation possible, and the implementation is expected to improve, but there will always be degenerate cases in which the stack can become very deep. This can be a problem in MSDOS and MS Windows 3.1 environments. (Of course, in a Unix or Windows 95/98/NT environment with a proper stack, this is not a problem at all.)

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        int red;
        im = gdImageCreate(100, 50);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Allocate the color red. */
        red = gdImageColorAllocate(im, 255, 0, 0);
        /* Inscribe an ellipse in the image. */
        gdImageArc(im, 50, 25, 98, 48, 0, 360, white);
        /* Flood-fill the ellipse. Fill color is red, border color is
        	white (ellipse). */
        gdImageFillToBorder(im, 50, 50, white, red);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageFill(gdImagePtr im, int x, int y, int color) (FUNCTION)
    gdImageFill floods a portion of the image with the specified `color`, beginning at the specified point and flooding the surrounding region of the same color as the starting point. For a way of flooding a region defined by a specific border color rather than by its interior color, see gdImageFillToBorder.

    The fill color can be gdTiled, resulting in a tile fill using another image as the tile. However, the tile image cannot be transparent. If the image you wish to fill with has a transparent color index, call gdImageTransparent on the tile image and set the transparent color index to -1 to turn off its transparency.

    Note that gdImageFill is recursive. It is not the most naive implementation possible, and the implementation is expected to improve, but there will always be degenerate cases in which the stack can become very deep. This can be a problem in MSDOS and MS Windows environments. (Of course, in a Unix or Windows 95/98/NT environment with a proper stack, this is not a problem at all.)

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        int red;
        im = gdImageCreate(100, 50);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Allocate the color red. */
        red = gdImageColorAllocate(im, 255, 0, 0);
        /* Inscribe an ellipse in the image. */
        gdImageArc(im, 50, 25, 98, 48, 0, 360, white);
        /* Flood-fill the ellipse. Fill color is red, and will replace the
        	black interior of the ellipse. */
        gdImageFill(im, 50, 50, red);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageSetBrush(gdImagePtr im, gdImagePtr brush) (FUNCTION)
    A "brush" is an image used to draw wide, shaped strokes in another image. Just as a paintbrush is not a single point, a brush image need not be a single pixel. Any gd image can be used as a brush, and by setting the transparent color index of the brush image with gdImageColorTransparent, a brush of any shape can be created. All line-drawing functions, such as gdImageLine and gdImagePolygon, will use the current brush if the special "color" gdBrushed or gdStyledBrushed is used when calling them.

    gdImageSetBrush is used to specify the brush to be used in a particular image. You can set any image to be the brush. If the brush image does not have the same color map as the first image, any colors missing from the first image will be allocated. If not enough colors can be allocated, the closest colors already available will be used. This allows arbitrary PNGs to be used as brush images. It also means, however, that you should not set a brush unless you will actually use it; if you set a rapid succession of different brush images, you can quickly fill your color map, and the results will not be optimal.

    You need not take any special action when you are finished with a brush. As for any other image, if you will not be using the brush image for any further purpose, you should call gdImageDestroy. You must not use the color gdBrushed if the current brush has been destroyed; you can of course set a new brush to replace it.

        ... inside a function ...
        gdImagePtr im, brush;
        FILE *in;
        int black;
        im = gdImageCreate(100, 100);
        /* Open the brush PNG. For best results, portions of the
        	brush that should be transparent (ie, not part of the
        	brush shape) should have the transparent color index. */
        in = fopen("star.png", "rb");
        brush = gdImageCreateFromPng(in);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        gdImageSetBrush(im, brush);
        /* Draw a line from the upper left corner to the lower right corner
        	using the brush. */
        gdImageLine(im, 0, 0, 99, 99, gdBrushed);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);
        /* Destroy the brush image */
        gdImageDestroy(brush);

  void gdImageSetTile(gdImagePtr im, gdImagePtr tile) (FUNCTION)
    A "tile" is an image used to fill an area with a repeated pattern. Any gd image can be used as a tile, and by setting the transparent color index of the tile image with gdImageColorTransparent, a tile that allows certain parts of the underlying area to shine through can be created. All region-filling functions, such as gdImageFill and gdImageFilledPolygon, will use the current tile if the special "color" gdTiled is used when calling them.

    gdImageSetTile is used to specify the tile to be used in a particular image. You can set any image to be the tile. If the tile image does not have the same color map as the first image, any colors missing from the first image will be allocated. If not enough colors can be allocated, the closest colors already available will be used. This allows arbitrary PNGs to be used as tile images. It also means, however, that you should not set a tile unless you will actually use it; if you set a rapid succession of different tile images, you can quickly fill your color map, and the results will not be optimal.

    You need not take any special action when you are finished with a tile. As for any other image, if you will not be using the tile image for any further purpose, you should call gdImageDestroy. You must not use the color gdTiled if the current tile has been destroyed; you can of course set a new tile to replace it.

        ... inside a function ...
        gdImagePtr im, tile;
        FILE *in;
        int black;
        im = gdImageCreate(100, 100);
        /* Open the tile PNG. For best results, portions of the
        	tile that should be transparent (ie, allowing the
        	background to shine through) should have the transparent
        	color index. */
        in = fopen("star.png", "rb");
        tile = gdImageCreateFromPng(in);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        gdImageSetTile(im, tile);
        /* Fill an area using the tile. */
        gdImageFilledRectangle(im, 25, 25, 75, 75, gdTiled);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);
        /* Destroy the tile image */
        gdImageDestroy(tile);

  void gdImageSetStyle(gdImagePtr im, int *style, int styleLength) (FUNCTION)
    It is often desirable to draw dashed lines, dotted lines, and other variations on a broken line. gdImageSetStyle can be used to set any desired series of colors, including a special color that leaves the background intact, to be repeated during the drawing of a line.

    To use gdImageSetStyle, create an array of integers and assign them the desired series of color values to be repeated. You can assign the special color value gdTransparent to indicate that the existing color should be left unchanged for that particular pixel (allowing a dashed line to be attractively drawn over an existing image).

    Then, to draw a line using the style, use the normal gdImageLine function with the special color value gdStyled.

    As of version 1.1.1, the style array is copied when you set the style, so you need not be concerned with keeping the array around indefinitely. This should not break existing code that assumes styles are not copied.

    You can also combine styles and brushes to draw the brush image at intervals instead of in a continuous stroke. When creating a style for use with a brush, the style values are interpreted differently: zero (0) indicates pixels at which the brush should not be drawn, while one (1) indicates pixels at which the brush should be drawn. To draw a styled, brushed line, you must use the special color value gdStyledBrushed. For an example of this feature in use, see gddemo.c (provided in the distribution).

        gdImagePtr im;
        int styleDotted[2], styleDashed[6];
        FILE *in;
        int black;
        int red;
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        red = gdImageColorAllocate(im, 255, 0, 0);
        /* Set up dotted style. Leave every other pixel alone. */
        styleDotted[0] = red;
        styleDotted[1] = gdTransparent;
        /* Set up dashed style. Three on, three off. */
        styleDashed[0] = red;
        styleDashed[1] = red;
        styleDashed[2] = red;
        styleDashed[3] = gdTransparent;
        styleDashed[4] = gdTransparent;
        styleDashed[5] = gdTransparent;
        /* Set dotted style. Note that we have to specify how many pixels are
        	in the style! */
        gdImageSetStyle(im, styleDotted, 2);
        /* Draw a line from the upper left corner to the lower right corner. */
        gdImageLine(im, 0, 0, 99, 99, gdStyled);
        /* Now the dashed line. */
        gdImageSetStyle(im, styleDashed, 6);
        gdImageLine(im, 0, 99, 0, 99, gdStyled);

        /* ... Do something with the image, such as saving it to a file ... */

        /* Destroy it */
        gdImageDestroy(im);

  void gdImageAlphaBlending(gdImagePtr im, int blending) (FUNCTION)
    The gdImageAlphaBlending function allows for two different modes of drawing on truecolor images. In blending mode, the alpha channel component of the color supplied to all drawing functions, such as gdImageSetPixel, determines how much of the underlying color should be allowed to shine through. As a result, gd automatically blends the existing color at that point with the drawing color, and stores the result in the image. The resulting pixel is opaque. In non-blending mode, the drawing color is copied literally with its alpha channel information, replacing the destination pixel. Blending mode is not available when drawing on palette images.

        gdImagePtr im;
        int red, blue;
        im = gdImageCreateTrueColor(100, 100);
        /* Background color */
        red = gdTrueColor(255, 0, 0);
        gdImageFilledRectangle(im, 0, 0, 100, 100, red);
        /* Drawing color. Full transparency would be an alpha channel value
        	of 127 (gd has a 7 bit alpha chnanel). 0 is opaque,
        	127 is transparent. So cut gdAlphaTransparent in half to get
        	50% blending. */
        blue = gdTrueColorAlpha(0, 0, 255, gdAlphaTransparent / 2);
        /* Draw with blending. Result will be 50% red, 50% blue: yellow
        	(emitted light, remember, not reflected light. What you learned
        	in Kindergarten is wrong here). */
        gdImageAlphaBlending(im, 1);
        gdImageFilledRectangle(im, 0, 0, 25, 25, blue);
        /* Draw without blending. Result will be 50% blue, 50%
        	the background color of the image viewer or web browser
        	used; results in browsers that don't support
        	semi-transparent pixels are unpredictable! */
        gdImageAlphaBlending(im, 0);
        gdImageFilledRectangle(im, 75, 75, 25, 25, blue);
        /* Write the image to disk, etc. */

  ### Query Functions

  int gdImageAlpha(gdImagePtr im, int color) (MACRO)
    gdImageAlpha is a macro which returns the alpha channel component of the specified color index. Alpha channel values vary between 0 (gdAlphaOpaque), which does not blend at all with the background, through 127 (gdAlphaTransparent), which allows the background to shine through 100%. Use this macro rather than accessing the structure members directly. int gdImageBlue(gdImagePtr im, int color) (MACRO)
    gdImageBlue is a macro which returns the blue component of the specified color index. Use this macro rather than accessing the structure members directly.
  int gdImageGetPixel(gdImagePtr im, int x, int y) (FUNCTION)
    gdImageGetPixel() retrieves the color index of a particular pixel. Always use this function to query pixels; do not access the pixels of the gdImage structure directly.

        ... inside a function ...
        FILE *in;
        gdImagePtr im;
        int c;
        in = fopen("mypng.png", "rb");
        im = gdImageCreateFromPng(in);
        fclose(in);
        c = gdImageGetPixel(im, gdImageSX(im) / 2, gdImageSY(im) / 2);
        printf("The value of the center pixel is %d; RGB values are %d,%d,%d\n",
        	c, im->red[c], im->green[c], im->blue[c]);
        gdImageDestroy(im);

  int gdImageBoundsSafe(gdImagePtr im, int x, int y) (FUNCTION)
    gdImageBoundsSafe returns true (1) if the specified point is within the bounds of the image, false (0) if not. This function is intended primarily for use by those who wish to add functions to gd. All of the gd drawing functions already clip safely to the edges of the image.

        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 100);
        if (gdImageBoundsSafe(im, 50, 50)) {
        	printf("50, 50 is within the image bounds\n");
        } else {
        	printf("50, 50 is outside the image bounds\n");
        }
        gdImageDestroy(im);

  int gdImageGreen(gdImagePtr im, int color) (MACRO)
    gdImageGreen is a macro which returns the green component of the specified color index. Use this macro rather than accessing the structure members directly.
  int gdImageRed(gdImagePtr im, int color) (MACRO)
    gdImageRed is a macro which returns the red component of the specified color index. Use this macro rather than accessing the structure members directly.
  int gdImageSX(gdImagePtr im) (MACRO)
    gdImageSX is a macro which returns the width of the image in pixels. Use this macro rather than accessing the structure members directly.
  int gdImageSY(gdImagePtr im) (MACRO)
    gdImageSY is a macro which returns the height of the image in pixels. Use this macro rather than accessing the structure members directly.

  ### Fonts and text-handling functions

  void gdImageChar(gdImagePtr im, gdFontPtr font, int x, int y, int c, int color) (FUNCTION)
    gdImageChar is used to draw single characters on the image. (To draw multiple characters, use gdImageString or gdImageString16. See also gdImageStringFT for a high quality solution.) The second argument is a pointer to a font definition structure; five fonts are provided with gd, gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge, and gdFontGiant. You must include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h" respectively and (if you are not using a library-based approach) link with the corresponding .c files to use the provided fonts. The character specified by the fifth argument is drawn from left to right in the specified color. (See gdImageCharUp for a way of drawing vertical text.) Pixels not set by a particular character retain their previous color.

        #include "gd.h"
        #include "gdfontl.h"
        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Draw a character. */
        gdImageChar(im, gdFontLarge, 0, 0, 'Q', white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageCharUp(gdImagePtr im, gdFontPtr font, int x, int y, int c, int color) (FUNCTION)
    gdImageCharUp is used to draw single characters on the image, rotated 90 degrees. (To draw multiple characters, use gdImageStringUp or gdImageStringUp16.) The second argument is a pointer to a font definition structure; five fonts are provided with gd, gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge, and gdFontGiant. You must include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h" respectively and (if you are not using a library-based approach) link with the corresponding .c files to use the provided fonts. The character specified by the fifth argument is drawn from bottom to top, rotated at a 90-degree angle, in the specified color. (See gdImageChar for a way of drawing horizontal text.) Pixels not set by a particular character retain their previous color.

        #include "gd.h"
        #include "gdfontl.h"
        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Draw a character upwards so it rests against the top of the image. */
        gdImageCharUp(im, gdFontLarge,
        	0, gdFontLarge->h, 'Q', white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageString(gdImagePtr im, gdFontPtr font, int x, int y, unsigned char *s, int color) (FUNCTION)
    gdImageString is used to draw multiple characters on the image. (To draw single characters, use gdImageChar.) The second argument is a pointer to a font definition structure; five fonts are provided with gd, gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge, and gdFontGiant. You must include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h" respectively and (if you are not using a library-based approach) link with the corresponding .c files to use the provided fonts. The null-terminated C string specified by the fifth argument is drawn from left to right in the specified color. (See gdImageStringUp for a way of drawing vertical text. See also gdImageStringFT for a high quality solution.) Pixels not set by a particular character retain their previous color.

        #include "gd.h"
        #include "gdfontl.h"
        #include <string.h>
        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        /* String to draw. */
        char *s = "Hello.";
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Draw a centered string. */
        gdImageString(im, gdFontLarge,
        	im->w / 2 - (strlen(s) * gdFontLarge->w / 2),
        	im->h / 2 - gdFontLarge->h / 2,
        	s, white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageString16(gdImagePtr im, gdFontPtr font, int x, int y, unsigned short *s, int color) (FUNCTION)
    gdImageString is used to draw multiple 16-bit characters on the image. (To draw single characters, use gdImageChar.) The second argument is a pointer to a font definition structure; five fonts are provided with gd, gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge, and gdFontGiant. You must include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h" respectively and (if you are not using a library-based approach) link with the corresponding .c files to use the provided fonts. The null-terminated string of characters represented as 16-bit unsigned short integers specified by the fifth argument is drawn from left to right in the specified color. (See gdImageStringUp16 for a way of drawing vertical text.) Pixels not set by a particular character retain their previous color.

    This function was added in gd1.3 to provide a means of rendering fonts with more than 256 characters for those who have them. A more frequently used routine is gdImageString.

  void gdImageStringUp(gdImagePtr im, gdFontPtr font, int x, int y, unsigned char *s, int color) (FUNCTION)
    gdImageStringUp is used to draw multiple characters on the image, rotated 90 degrees. (To draw single characters, use gdImageCharUp.) The second argument is a pointer to a font definition structure; five fonts are provided with gd, gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge, and gdFontGiant. You must include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h" respectively and (if you are not using a library-based approach) link with the corresponding .c files to use the provided fonts.The null-terminated C string specified by the fifth argument is drawn from bottom to top (rotated 90 degrees) in the specified color. (See gdImageString for a way of drawing horizontal text.) Pixels not set by a particular character retain their previous color.

        #include "gd.h"
        #include "gdfontl.h"
        #include <string.h>
        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        /* String to draw. */
        char *s = "Hello.";
        im = gdImageCreate(100, 100);
        /* Background color (first allocated) */
        black = gdImageColorAllocate(im, 0, 0, 0);
        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        /* Draw a centered string going upwards. Axes are reversed,
        	and Y axis is decreasing as the string is drawn. */
        gdImageStringUp(im, gdFontLarge,
        	im->w / 2 - gdFontLarge->h / 2,
        	im->h / 2 + (strlen(s) * gdFontLarge->w / 2),
        	s, white);
        /* ... Do something with the image, such as saving it to a file... */
        /* Destroy it */
        gdImageDestroy(im);

  void gdImageStringUp16(gdImagePtr im, gdFontPtr font, int x, int y, unsigned short *s, int color) (FUNCTION)
    gdImageString is used to draw multiple 16-bit characters vertically on the image. (To draw single characters, use gdImageChar.) The second argument is a pointer to a font definition structure; five fonts are provided with gd, gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge, and gdFontGiant. You must include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h" respectively and (if you are not using a library-based approach) link with the corresponding .c files to use the provided fonts. The null-terminated string of characters represented as 16-bit unsigned short integers specified by the fifth argument is drawn from bottom to top in the specified color. (See gdImageStringUp16 for a way of drawing horizontal text.) Pixels not set by a particular character retain their previous color.

    This function was added in gd1.3 to provide a means of rendering fonts with more than 256 characters for those who have them. A more frequently used routine is gdImageStringUp.

  char *gdImageStringFT(gdImagePtr im, int *brect, int fg, char *fontname, double ptsize, double angle, int x, int y, char *string) (FUNCTION)
    RECOMMENDED. New in 1.8.4. gdImageStringFT draws text using the FreeType 2.x library.

    gdImageStringFT draws a string of anti-aliased characters on the image using the FreeType library to render user-supplied TrueType fonts. We do not provide TrueType fonts (.ttf and .ttc files). Obtaining them is entirely up to you. The string is anti-aliased, meaning that there should be fewer "jaggies" visible. The fontname is the full pathname to a TrueType font file, or a font face name if the GDFONTPATH environment variable or FreeType's DEFAULT_FONTPATH variable have been set intelligently. The string may be arbitrarily scaled (ptsize) and rotated (angle in radians).

    The user-supplied int brect[8] array is filled on return from gdImageStringFT with the 8 elements representing the 4 corner coordinates of the bounding rectangle.

    0 | lower left corner, X position
    lower left corner, Y position
    lower right corner, X position
    3 | lower right corner, Y position
    4 | upper right corner, X position
    5 | upper right corner, Y position
    6 | upper left corner, X position
    7 | upper left corner, Y position

    The points are relative to the text regardless of the angle, so "upper left" means in the top left-hand corner seeing the text horizontally.

    Use a NULL gdImagePtr to get the bounding rectangle without rendering. This is a relatively cheap operation if followed by a rendering of the same string, because of the caching of the partial rendering during bounding rectangle calculation.

    The string is rendered in the color indicated by the gf color index. Use the negative of the desired color index to disable anti-aliasing.

    The string may contain UTF-8 sequences like: "&#192;"

    gdImageStringFT will return a null char* on success, or an error string on failure.

        #include "gd.h"
        #include <string.h>
        ... inside a function ...
        gdImagePtr im;
        int black;
        int white;
        int brect[8];
        int x, y;
        char *err;

        char *s = "Hello."; /* String to draw. */
        double sz = 40.;
        char *f = "/usr/local/share/ttf/Times.ttf";  /* User supplied font */

        /* obtain brect so that we can size the image */
        err = gdImageStringFT(NULL,&brect[0],0,f,sz,0.,0,0,s);
        if (err) {fprintf(stderr,err); return 1;}

        /* create an image big enough for the string plus a little whitespace */
        x = brect[2]-brect[6] + 6;
        y = brect[3]-brect[7] + 6;
        im = gdImageCreate(x,y);

        /* Background color (first allocated) */
        white = gdImageColorResolve(im, 255, 255, 255);
        black = gdImageColorResolve(im, 0, 0, 0);

        /* render the string, offset origin to center string*/
        /* note that we use top-left coordinate for adjustment
         * since gd origin is in top-left with y increasing downwards. */
        x = 3 - brect[6];
        y = 3 - brect[7];
        err = gdImageStringFT(im,&brect[0],black,f,sz,0.0,x,y,s);
        if (err) {fprintf(stderr,err); return 1;}

        /* Write img to stdout */
        gdImagePng(im, stdout);

        /* Destroy it */
        gdImageDestroy(im);

  char *gdImageStringTTF(gdImagePtr im, int *brect, int fg, char *fontname, double ptsize, double angle, int x, int y, char *string) (FUNCTION)
    DEPRECATED. THis function simply invokes gdImageStringFT for backwards compatibility with old code that was written with FreeType 1.x. /DL>

    ### Color-handling functions

    int gdImageColorAllocate(gdImagePtr im, int r, int g, int b) (FUNCTION)
      gdImageColorAllocate finds the first available color index in the image specified, sets its RGB values to those requested (255 is the maximum for each), and returns the index of the new color table entry, or an RGBA value in the case of a truecolor image; in either case you can then use the returned value as a parameter to drawing functions. When creating a new palette-based image, the first time you invoke this function, you are setting the background color for that image.

      In the event that all gdMaxColors colors (256) have already been allocated, gdImageColorAllocate will return -1 to indicate failure. (This is not uncommon when working with existing PNG files that already use 256 colors.) Note that gdImageColorAllocate does not check for existing colors that match your request; see gdImageColorExact, gdImageColorClosest and gdImageColorClosestHWB for ways to locate existing colors that approximate the color desired in situations where a new color is not available. Also see gdImageColorResolve, new in gd-1.6.2.

          ... inside a function ...
          gdImagePtr im;
          int black;
          int red;
          im = gdImageCreate(100, 100);
          /* Background color (first allocated) */
          black = gdImageColorAllocate(im, 0, 0, 0);
          /* Allocate the color red. */
          red = gdImageColorAllocate(im, 255, 0, 0);
          /* Draw a dashed line from the upper left corner to the lower right corner. */
          gdImageDashedLine(im, 0, 0, 99, 99, red);
          /* ... Do something with the image, such as saving it to a file... */
          /* Destroy it */
          gdImageDestroy(im);

    int gdImageColorAllocateAlpha(gdImagePtr im, int r, int g, int b, int a) (FUNCTION)
      gdImageColorAllocateAlpha finds the first available color index in the image specified, sets its RGBA values to those requested (255 is the maximum for red, green and blue, and 127 represents full transparency for alpha), and returns the index of the new color table entry, or an RGBA value in the case of a truecolor image; in either case you can then use the returned value as a parameter to drawing functions. When creating a new palette-based image, the first time you invoke this function, you are setting the background color for that image.

      In the event that all gdMaxColors colors (256) have already been allocated, gdImageColorAllocate will return -1 to indicate failure. (This is not uncommon when working with existing palette-based PNG files that already use 256 colors.) Note that gdImageColorAllocateAlpha does not check for existing colors that match your request; see gdImageColorExactAlpha and gdImageColorClosestAlpha for ways to locate existing colors that approximate the color desired in situations where a new color is not available. Also see gdImageColorResolveAlpha.

          ... inside a function ...
          gdImagePtr im;
          int black;
          int red;
          im = gdImageCreate(100, 100);
          /* Background color (first allocated) */
          black = gdImageColorAllocate(im, 0, 0, 0);
          /* Allocate the color red, 50% transparent. */
          red = gdImageColorAllocateAlpha(im, 255, 0, 0, 64);
          /* Draw a dashed line from the upper left corner to the lower right corner. */
          gdImageDashedLine(im, 0, 0, 99, 99, red);
          /* ... Do something with the image, such as saving it to a file... */
          /* Destroy it */
          gdImageDestroy(im);

    int gdImageColorClosest(gdImagePtr im, int r, int g, int b) (FUNCTION)
      gdImageColorClosest searches the colors which have been defined thus far in the image specified and returns the index of the color with RGB values closest to those of the request. (Closeness is determined by Euclidian distance, which is used to determine the distance in three-dimensional color space between colors.)

      If no colors have yet been allocated in the image, gdImageColorClosest returns -1.

      When applied to a truecolor image, this function always succeeds in returning the desired color.

      This function is most useful as a backup method for choosing a drawing color when an image already contains gdMaxColors (256) colors and no more can be allocated. (This is not uncommon when working with existing PNG files that already use many colors.) See gdImageColorExact for a method of locating exact matches only.

          ... inside a function ...
          gdImagePtr im;
          FILE *in;
          int red;
          /* Let's suppose that photo.png is a scanned photograph with
          	many colors. */
          in = fopen("photo.png", "rb");
          im = gdImageCreateFromPng(in);
          fclose(in);
          /* Try to allocate red directly */
          red = gdImageColorAllocate(im, 255, 0, 0);
          /* If we fail to allocate red... */
          if (red == (-1)) {
          	/* Find the closest color instead. */
          	red = gdImageColorClosest(im, 255, 0, 0);
          }
          /* Draw a dashed line from the upper left corner to the lower right corner */
          gdImageDashedLine(im, 0, 0, 99, 99, red);
          /* ... Do something with the image, such as saving it to a file... */
          /* Destroy it */
          gdImageDestroy(im);

    int gdImageColorClosestAlpha(gdImagePtr im, int r, int g, int b, int a) (FUNCTION)
      gdImageColorClosest searches the colors which have been defined thus far in the image specified and returns the index of the color with RGBA values closest to those of the request. (Closeness is determined by Euclidian distance, which is used to determine the distance in four-dimensional color/alpha space between colors.)

      If no colors have yet been allocated in the image, gdImageColorClosestAlpha returns -1.

      When applied to a truecolor image, this function always succeeds in returning the desired color.

      This function is most useful as a backup method for choosing a drawing color when a palette-based image already contains gdMaxColors (256) colors and no more can be allocated. (This is not uncommon when working with existing palette-based PNG files that already use many colors.) See gdImageColorExactAlpha for a method of locating exact matches only.

          ... inside a function ...
          gdImagePtr im;
          FILE *in;
          int red;
          /* Let's suppose that photo.png is a scanned photograph with
          	many colors. */
          in = fopen("photo.png", "rb");
          im = gdImageCreateFromPng(in);
          fclose(in);
          /* Try to allocate red, 50% transparent, directly */
          red = gdImageColorAllocateAlpha(im, 255, 0, 0, 64);
          /* If we fail to allocate red... */
          if (red == (-1)) {
          	/* Find the closest color instead. */
          	red = gdImageColorClosestAlpha(im, 255, 0, 0, 64);
          }
          /* Draw a dashed line from the upper left corner to the lower right corner */
          gdImageDashedLine(im, 0, 0, 99, 99, red);
          /* ... Do something with the image, such as saving it to a file... */
          /* Destroy it */
          gdImageDestroy(im);

    int gdImageColorClosestHWB(gdImagePtr im, int r, int g, int b) (FUNCTION)
      gdImageColorClosestHWB searches the colors which have been defined thus far in the image specified and returns the index of the color with hue, whiteness and blackness closest to the requested color. This scheme is typically superior to the Euclidian distance scheme used by gdImageColorClosest.

      If no colors have yet been allocated in the image, gdImageColorClosestHWB returns -1.

      When applied to a truecolor image, this function always succeeds in returning the desired color.

      This function is most useful as a backup method for choosing a drawing color when an image already contains gdMaxColors (256) colors and no more can be allocated. (This is not uncommon when working with existing PNG files that already use many colors.) See gdImageColorExact for a method of locating exact matches only.

          ... inside a function ...
          gdImagePtr im;
          FILE *in;
          int red;
          /* Let's suppose that photo.png is a scanned photograph with
          	many colors. */
          in = fopen("photo.png", "rb");
          im = gdImageCreateFromPng(in);
          fclose(in);
          /* Try to allocate red directly */
          red = gdImageColorAllocate(im, 255, 0, 0);
          /* If we fail to allocate red... */
          if (red == (-1)) {
          	/* Find the closest color instead. */
          	red = gdImageColorClosestHWB(im, 255, 0, 0);
          }
          /* Draw a dashed line from the upper left corner to the lower right corner */
          gdImageDashedLine(im, 0, 0, 99, 99, red);
          /* ... Do something with the image, such as saving it to a file... */
          /* Destroy it */
          gdImageDestroy(im);

    int gdImageColorExact(gdImagePtr im, int r, int g, int b) (FUNCTION)
      gdImageColorExact searches the colors which have been defined thus far in the image specified and returns the index of the first color with RGB values which exactly match those of the request. If no allocated color matches the request precisely, gdImageColorExact returns -1. See gdImageColorClosest for a way to find the color closest to the color requested.

      When applied to a truecolor image, this function always succeeds in returning the desired color.

          ... inside a function ...
          gdImagePtr im;
          int red;
          in = fopen("photo.png", "rb");
          im = gdImageCreateFromPng(in);
          fclose(in);
          /* The image may already contain red; if it does, we'll save a slot
          	in the color table by using that color. */
          /* Try to allocate red directly */
          red = gdImageColorExact(im, 255, 0, 0);
          /* If red isn't already present... */
          if (red == (-1)) {
          	/* Second best: try to allocate it directly. */
          	red = gdImageColorAllocate(im, 255, 0, 0);
          	/* Out of colors, so find the closest color instead. */
          	red = gdImageColorClosest(im, 255, 0, 0);
          }
          /* Draw a dashed line from the upper left corner to the lower right corner */
          gdImageDashedLine(im, 0, 0, 99, 99, red);
          /* ... Do something with the image, such as saving it to a file... */
          /* Destroy it */
          gdImageDestroy(im);

    int gdImageColorResolve(gdImagePtr im, int r, int g, int b) (FUNCTION)
      gdImageColorResolve searches the colors which have been defined thus far in the image specified and returns the index of the first color with RGB values which exactly match those of the request. If no allocated color matches the request precisely, then gdImageColorResolve tries to allocate the exact color. If there is no space left in the color table then gdImageColorResolve returns the closest color (as in gdImageColorClosest). This function always returns an index of a color.

      When applied to a truecolor image, this function always succeeds in returning the desired color.

          ... inside a function ...
          gdImagePtr im;
          int red;
          in = fopen("photo.png", "rb");
          im = gdImageCreateFromPng(in);
          fclose(in);
          /* The image may already contain red; if it does, we'll save a slot
          	in the color table by using that color. */
          /* Get index of red, or color closest to red */
          red = gdImageColorResolve(im, 255, 0, 0);
          /* Draw a dashed line from the upper left corner to the lower right corner */
          gdImageDashedLine(im, 0, 0, 99, 99, red);
          /* ... Do something with the image, such as saving it to a file... */
          /* Destroy it */
          gdImageDestroy(im);

    int gdImageColorResolveAlpha(gdImagePtr im, int r, int g, int b, int a) (FUNCTION)
      gdImageColorResolveAlpha searches the colors which have been defined thus far in the image specified and returns the index of the first color with RGBA values which exactly match those of the request. If no allocated color matches the request precisely, then gdImageColorResolveAlpha tries to allocate the exact color. If there is no space left in the color table then gdImageColorResolveAlpha returns the closest color (as in gdImageColorClosestAlpha). This function always returns an index of a color.

      When applied to a truecolor image, this function always succeeds in returning the desired color.

          ... inside a function ...
          gdImagePtr im;
          int red;
          in = fopen("photo.png", "rb");
          im = gdImageCreateFromPng(in);
          fclose(in);
          /* The image may already contain red; if it does, we'll save a slot
          	in the color table by using that color. */
          /* Get index of red, 50% transparent, or the next best thing */
          red = gdImageColorResolveAlpha(im, 255, 0, 0, 64);
          /* Draw a dashed line from the upper left corner to the lower right corner */
          gdImageDashedLine(im, 0, 0, 99, 99, red);
          /* ... Do something with the image, such as saving it to a file... */
          /* Destroy it */
          gdImageDestroy(im);

    int gdImageColorsTotal(gdImagePtr im) (MACRO)
      gdImageColorsTotal is a macro which returns the number of colors currently allocated in a palette image. For truecolor images, the result of this call is undefined and should not be used.
    int gdImageColorRed(gdImagePtr im, int c) (MACRO)
      gdImageColorRed is a macro which returns the red portion of the specified color in the image. This macro works for both palette and truecolor images.
    int gdImageColorGreen(gdImagePtr im, int c) (MACRO)
      gdImageColorGreen is a macro which returns the green portion of the specified color in the image. This macro works for both palette and truecolor images.
    int gdImageColorBlue(gdImagePtr im, int c) (MACRO)
      gdImageColorBlue is a macro which returns the green portion of the specified color in the image. This macro works for both palette and truecolor images.
    int gdImageGetInterlaced(gdImagePtr im) (MACRO)
      gdImageGetInterlaced is a macro which returns true (1) if the image is interlaced, false (0) if not. Use this macro to obtain this information; do not access the structure directly. See gdImageInterlace for a means of interlacing images.
    int gdImageGetTransparent(gdImagePtr im) (MACRO)
      gdImageGetTransparent is a macro which returns the current transparent color index in the image. If there is no transparent color, gdImageGetTransparent returns -1. Use this macro to obtain this information; do not access the structure directly.
    void gdImageColorDeallocate(gdImagePtr im, int color) (FUNCTION)
      gdImageColorDeallocate marks the specified color as being available for reuse. It does not attempt to determine whether the color index is still in use in the image. After a call to this function, the next call to gdImageColorAllocate for the same image will set new RGB values for that color index, changing the color of any pixels which have that index as a result. If multiple calls to gdImageColorDeallocate are made consecutively, the lowest-numbered index among them will be reused by the next gdImageColorAllocate call.

          ... inside a function ...
          gdImagePtr im;
          int red, blue;
          in = fopen("photo.png", "rb");
          im = gdImageCreateFromPng(in);
          fclose(in);
          /* Look for red in the color table. */
          red = gdImageColorExact(im, 255, 0, 0);
          /* If red is present... */
          if (red != (-1)) {
          	/* Deallocate it. */
          	gdImageColorDeallocate(im, red);
          	/* Allocate blue, reusing slot in table.
          		Existing red pixels will change color. */
          	blue = gdImageColorAllocate(im, 0, 0, 255);
          }
          /* ... Do something with the image, such as saving it to a file... */
          /* Destroy it */
          gdImageDestroy(im);

    void gdImageColorTransparent(gdImagePtr im, int color) (FUNCTION)
      gdImageColorTransparent sets the transparent color index for the specified image to the specified index. To indicate that there should be no transparent color, invoke gdImageColorTransparent with a color index of -1. Note that JPEG images do not support transparency, so this setting has no effect when writing JPEG images.

      The color index used should be an index allocated by gdImageColorAllocate, whether explicitly invoked by your code or implicitly invoked by loading an image. In order to ensure that your image has a reasonable appearance when viewed by users who do not have transparent background capabilities (or when you are writing a JPEG-format file, which does not support transparency), be sure to give reasonable RGB values to the color you allocate for use as a transparent color, even though it will be transparent on systems that support PNG transparency.

          ... inside a function ...
          gdImagePtr im;
          int black;
          FILE *in, *out;
          in = fopen("photo.png", "rb");
          im = gdImageCreateFromPng(in);
          fclose(in);
          /* Look for black in the color table and make it transparent. */
          black = gdImageColorExact(im, 0, 0, 0);
          /* If black is present... */
          if (black != (-1)) {
          	/* Make it transparent */
          	gdImageColorTransparent(im, black);
          }
          /* Save the newly-transparent image back to the file */
          out = fopen("photo.png", "wb");
          gdImagePng(im, out);
          fclose(out);
          /* Destroy it */
          gdImageDestroy(im);

    void gdImageTrueColor(int red, int green, int blue) (MACRO)
      gdImageTrueColor returns an RGBA color value for use when drawing on a truecolor image. Red, green, and blue are all in the range between 0 (off) and 255 (maximum). This macro should not be used with palette-based images. If you need to write code which is compatible with both palette-based and truecolor images, use gdImageColorResolve.
    void gdImageTrueColorAlpha(int red, int green, int blue, int alpha) (MACRO)
      gdImageTrueColorAlpha returns an RGBA color value for use when drawing on a truecolor image with alpha channel transparency. Red, green, and blue are all in the range between 0 (off) and 255 (maximum). Alpha is in the range between 0 (opaque) and 127 (fully transparent). This macro should not be used with palette-based images. If you need to write code which is compatible with both palette-based and truecolor images, use gdImageColorResolveAlpha.

    ### Copying and resizing functions

    void gdImageCopy(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int w, int h) (FUNCTION)
      gdImageCopy is used to copy a rectangular portion of one image to another image. (For a way of stretching or shrinking the image in the process, see gdImageCopyResized.)

      The `dst` argument is the destination image to which the region will be copied. The `src` argument is the source image from which the region is copied. The `dstX` and `dstY` arguments specify the point in the destination image to which the region will be copied. The `srcX` and `srcY` arguments specify the upper left corner of the region in the source image. The `w` and `h` arguments specify the width and height of the region.

      When you copy a region from one location in an image to another location in the same image, gdImageCopy will perform as expected unless the regions overlap, in which case the result is unpredictable.

      Important note on copying between images: since different images do not necessarily have the same color tables, pixels are not simply set to the same color index values to copy them. gdImageCopy will attempt to find an identical RGB value in the destination image for each pixel in the copied portion of the source image by invoking gdImageColorExact. If such a value is not found, gdImageCopy will attempt to allocate colors as needed using gdImageColorAllocate. If both of these methods fail, gdImageCopy will invoke gdImageColorClosest to find the color in the destination image which most closely approximates the color of the pixel being copied.

          ... Inside a function ...
          gdImagePtr im_in;
          gdImagePtr im_out;
          int x, y;
          FILE *in;
          FILE *out;
          /* Load a small png to tile the larger one with */
          in = fopen("small.png", "rb");
          im_in = gdImageCreateFromPng(in);
          fclose(in);
          /* Make the output image four times as large on both axes */
          im_out = gdImageCreate(im_in->sx * 4, im_in->sy * 4);
          /* Now tile the larger image using the smaller one */
          for (y = 0; (y < 4); y++) {
          	for (x = 0; (x < 4); x++) {
          		gdImageCopy(im_out, im_in,
          			x * im_in->sx, y * im_in->sy,
          			0, 0,
          			im_in->sx, im_in->sy);
          	}
          }
          out = fopen("tiled.png", "wb");
          gdImagePng(im_out, out);
          fclose(out);
          gdImageDestroy(im_in);
          gdImageDestroy(im_out);

    void gdImageCopyResized(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int destW, int destH, int srcW, int srcH) (FUNCTION)
      gdImageCopyResized is used to copy a rectangular portion of one image to another image. The X and Y dimensions of the original region and the destination region can vary, resulting in stretching or shrinking of the region as appropriate. (For a simpler version of this function which does not deal with resizing, see gdImageCopy.)

      The `dst` argument is the destination image to which the region will be copied. The `src` argument is the source image from which the region is copied. The `dstX` and `dstY` arguments specify the point in the destination image to which the region will be copied. The `srcX` and `srcY` arguments specify the upper left corner of the region in the source image. The `dstW` and `dstH` arguments specify the width and height of the destination region. The `srcW` and `srcH` arguments specify the width and height of the source region and can differ from the destination size, allowing a region to be scaled during the copying process.

      When you copy a region from one location in an image to another location in the same image, gdImageCopy will perform as expected unless the regions overlap, in which case the result is unpredictable. If this presents a problem, create a scratch image in which to keep intermediate results.

      Important note on copying between images: since images do not necessarily have the same color tables, pixels are not simply set to the same color index values to copy them. gdImageCopy will attempt to find an identical RGB value in the destination image for each pixel in the copied portion of the source image by invoking gdImageColorExact. If such a value is not found, gdImageCopy will attempt to allocate colors as needed using gdImageColorAllocate. If both of these methods fail, gdImageCopy will invoke gdImageColorClosest to find the color in the destination image which most closely approximates the color of the pixel being copied.

          ... Inside a function ...
          gdImagePtr im_in;
          gdImagePtr im_out;
          int x, y;
          FILE *in;
          FILE *out;
          /* Load a small png to expand in the larger one */
          in = fopen("small.png", "rb");
          im_in = gdImageCreateFromPng(in);
          fclose(in);
          /* Make the output image four times as large on both axes */
          im_out = gdImageCreate(im_in->sx * 4, im_in->sy * 4);
          /* Now copy the smaller image, but four times larger */
          gdImageCopyResized(im_out, im_in, 0, 0, 0, 0,
          	im_out->sx, im_out->sy,
          	im_in->sx, im_in->sy);
          out = fopen("large.png", "wb");
          gdImagePng(im_out, out);
          fclose(out);
          gdImageDestroy(im_in);
          gdImageDestroy(im_out);

    void gdImageCopyResampled(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int destW, int destH, int srcW, int srcH) (FUNCTION)
      gdImageCopyResampled is used to copy a rectangular portion of one image to another image, smoothly interpolating pixel values so that, in particular, reducing the size of an image still retains a great deal of clarity. The X and Y dimensions of the original region and the destination region can vary, resulting in stretching or shrinking of the region as appropriate. (For a simpler version of this function which does not deal with resizing, see gdImageCopy. For a version which does not interpolate pixel values, see gdImageCopyResized.

      Pixel values are only interpolated if the destination image is a truecolor image. Otherwise, gdImageCopyResized is automatically invoked.

      The `dst` argument is the destination image to which the region will be copied. The `src` argument is the source image from which the region is copied. The `dstX` and `dstY` arguments specify the point in the destination image to which the region will be copied. The `srcX` and `srcY` arguments specify the upper left corner of the region in the source image. The `dstW` and `dstH` arguments specify the width and height of the destination region. The `srcW` and `srcH` arguments specify the width and height of the source region and can differ from the destination size, allowing a region to be scaled during the copying process.

      When you copy a region from one location in an image to another location in the same image, gdImageCopy will perform as expected unless the regions overlap, in which case the result is unpredictable. If this presents a problem, create a scratch image in which to keep intermediate results.

      Important note on copying between images: since images do not necessarily have the same color tables, pixels are not simply set to the same color index values to copy them. If the destination image is a palette image, gd will use the gdImageColorResolve function to determine the best color available.

          ... Inside a function ...
          gdImagePtr im_in;
          gdImagePtr im_out;
          int x, y;
          FILE *in;
          FILE *out;
          /* Load a large png to shrink in the smaller one */
          in = fopen("large.png", "rb");
          im_in = gdImageCreateFromPng(in);
          fclose(in);
          /* Make the output image four times as small on both axes. Use
          	a true color image so that we can interpolate colors. */
          im_out = gdImageCreateTrueColor(im_in->sx / 4, im_in->sy / 4);
          /* Now copy the large image, but four times smaller */
          gdImageCopyResampled(im_out, im_in, 0, 0, 0, 0,
          	im_out->sx, im_out->sy,
          	im_in->sx, im_in->sy);
          out = fopen("large.png", "wb");
          gdImagePng(im_out, out);
          fclose(out);
          gdImageDestroy(im_in);
          gdImageDestroy(im_out);

    void gdImageCopyMerge(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int w, int h, int pct) (FUNCTION)
      gdImageCopyMerge is almost identical to gdImageCopy, except that it 'merges' the two images by an amount specified in the last parameter. If the last parameter is 100, then it will function identically to gdImageCopy - the source image replaces the pixels in the destination.

      If, however, the pct parameter is less than 100, then the two images are merged. With pct = 0, no action is taken.

      This feature is most useful to 'highlight' sections of an image by merging a solid color with pct = 50:

          ... Inside a function ...
          gdImageCopyMerge(im_out, im_in, 100, 200, 0, 0, 30, 50, 50);

    void gdImageCopyMergeGray(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int w, int h, int pct) (FUNCTION)
      gdImageCopyMergeGray is almost identical to gdImageCopyMerge, except that when merging images it preserves the hue of the source by converting the destination pixels to grey scale before the copy operation.

          ... Inside a function ...
          gdImageCopyMergeGray(im_out, im_in, 100, 200, 0, 0, 30, 50, 50);

    void gdImagePaletteCopy(gdImagePtr dst, gdImagePtr src) (FUNCTION)
      Copies a palette from one image to another, attempting to match the colors in the target image to the colors in the source palette.

    ### Miscellaneous Functions

    int gdImageCompare(gdImagePtr im1, gdImagePtr im2) (FUNCTION)
      gdImageCompare returns a bitmap indicating if the two images are different. The members of the bitmap are defined in gd.h, but the most important is GD_CMP_IMAGE, which indicated that the images will actually appear different when displayed. Other, less important, differences relate to pallette entries. Any difference in the transparent colour is assumed to make images display differently, even if the transparent colour is not used.

          ... Inside a function ...
          cmpMask = gdImageCompare(im1, im2);

    gdImageInterlace(gdImagePtr im, int interlace) (FUNCTION)
      gdImageInterlace is used to determine whether an image should be stored in a linear fashion, in which lines will appear on the display from first to last, or in an interlaced fashion, in which the image will "fade in" over several passes. By default, images are not interlaced. (When writing JPEG images, interlacing implies generating progressive JPEG files, which are represented as a series of scans of increasing quality. Noninterlaced gd images result in regular [sequential] JPEG data streams.)

      A nonzero value for the interlace argument turns on interlace; a zero value turns it off. Note that interlace has no effect on other functions, and has no meaning unless you save the image in PNG or JPEG format; the gd and xbm formats do not support interlace.

      When a PNG is loaded with gdImageCreateFromPng or a JPEG is loaded with gdImageCreateFromJpeg, interlace will be set according to the setting in the PNG or JPEG file.

      Note that many PNG and JPEG viewers and web browsers do not support interlace or the incremental display of progressive JPEGs. However, the interlaced PNG or progressive JPEG should still display; it will simply appear all at once, just as other images do.

          gdImagePtr im;
          FILE *out;
          /* ... Create or load the image... */

          /* Now turn on interlace */
          gdImageInterlace(im, 1);
          /* And open an output file */
          out = fopen("test.png", "wb");
          /* And save the image  -- could also use gdImageJpeg */
          gdImagePng(im, out);
          fclose(out);
          gdImageDestroy(im);

    gdFree(void *ptr) (FUNCTION)
      gdFree provides a reliable way to free memory allocated by functions such as gdImagePngPtr which return blocks of memory. Use of this function guarantees that the version of `free()` that is ultimately called will be intended for use with the version of `malloc()` that originally allocated the block.

    ### Constants

    gdBrushed (CONSTANT)
      Used in place of a color when invoking a line-drawing function such as gdImageLine or gdImageRectangle. When gdBrushed is used as the color, the brush image set with gdImageSetBrush is drawn in place of each pixel of the line (the brush is usually larger than one pixel, creating the effect of a wide paintbrush). See also gdStyledBrushed for a way to draw broken lines with a series of distinct copies of an image.
    `gdMaxColors`(CONSTANT)
      The constant 256. This is the maximum number of colors in a PNG file according to the PNG standard, and is also the maximum number of colors in a gd image.
    gdStyled (CONSTANT)
      Used in place of a color when invoking a line-drawing function such as gdImageLine or gdImageRectangle. When gdStyled is used as the color, the colors of the pixels are drawn successively from the style that has been set with gdImageSetStyle. If the color of a pixel is equal to gdTransparent, that pixel is not altered. (This mechanism is completely unrelated to the "transparent color" of the image itself; see gdImageColorTransparent gdImageColorTransparent for that mechanism.) See also gdStyledBrushed.
    gdStyledBrushed (CONSTANT)
      Used in place of a color when invoking a line-drawing function such as gdImageLine or gdImageRectangle. When gdStyledBrushed is used as the color, the brush image set with gdImageSetBrush is drawn at each pixel of the line, providing that the style set with gdImageSetStyle contains a nonzero value (OR gdTransparent, which does not equal zero but is supported for consistency) for the current pixel. (Pixels are drawn successively from the style as the line is drawn, returning to the beginning when the available pixels in the style are exhausted.) Note that this differs from the behavior of gdStyled, in which the values in the style are used as actual pixel colors, except for gdTransparent.
    gdDashSize (CONSTANT)
      The length of a dash in a dashed line. Defined to be 4 for backwards compatibility with programs that use gdImageDashedLine. New programs should use gdImageSetStyle and call the standard gdImageLine function with the special "color" gdStyled or gdStyledBrushed.
    gdTiled (CONSTANT)
      Used in place of a normal color in gdImageFilledRectangle, gdImageFilledPolygon, gdImageFill, and gdImageFillToBorder. gdTiled selects a pixel from the tile image set with gdImageSetTile in such a way as to ensure that the filled area will be tiled with copies of the tile image. See the discussions of gdImageFill and gdImageFillToBorder for special restrictions regarding those functions.
    gdTransparent (CONSTANT)
      Used in place of a normal color in a style to be set with gdImageSetStyle. gdTransparent is not the transparent color index of the image; for that functionality please see gdImageColorTransparent.

    ### About the additional .gd image file format

    In addition to reading and writing the PNG and JPEG formats and reading the X Bitmap format, gd has the capability to read and write its own ".gd" format. This format is not intended for general purpose use and should never be used to distribute images. It is not a compressed format. Its purpose is solely to allow very fast loading of images your program needs often in order to build other images for output. If you are experiencing performance problems when loading large, fixed PNG images your program needs to produce its output images, you may wish to examine the functions gdImageCreateFromGd and gdImageGd, which read and write .gd format images.

    The program "pngtogd.c" is provided as a simple way of converting .png files to .gd format. I emphasize again that you will not need to use this format unless you have a need for high-speed loading of a few frequently-used images in your program.

    ### About the .gd2 image file format

    In addition to reading and writing the PNG format and reading the X Bitmap format, gd has the capability to read and write its own ".gd2" format. This format is not intended for general purpose use and should never be used to distribute images. It is a compressed format allowing pseudo-random access to large image files. Its purpose is solely to allow very fast loading of parts of images If you are experiencing performance problems when loading large, fixed PNG or JPEG images your program needs to produce its output images, you may wish to examine the functions gdImageCreateFromGd2, gdImageCreateFromGd2Part and gdImageGd2, which read and write .gd2 format images.

    The program "pngtogd2.c" is provided as a simple way of converting .png files to .gd2 format.

    ### About the gdIOCtx structure

    Version 1.5 of GD added a new style of I/O based on an IOCtx structure (the most up-to-date version can be found in gd_io.h):

        typedef struct gdIOCtx {
                int     (*getC)(struct gdIOCtx*);
                int     (*getBuf)(struct gdIOCtx*, void*, int);

                void     (*putC)(struct gdIOCtx*, int);
                int     (*putBuf)(struct gdIOCtx*, const void*, int);

                int     (*seek)(struct gdIOCtx*, const int);
                long    (*tell)(struct gdIOCtx*);

                void    (*free)(struct gdIOCtx*);

        } gdIOCtx;

    Most functions that accepted files in previous versions now also have a counterpart that accepts an I/O context. These functions have a 'Ctx' suffix.

    The <xxx>Ctx routines use the function pointers in the I/O context pointed to by gdIOCtx to perform all I/O. Examples of how to implement an I/O context can be found in io_file.c (which provides a wrapper for file routines), and io_dp.c (which implements in-memory storage).

    It is not necessary to implement all functions in an I/O context if you know that it will only be used in limited cirsumstances. At the time of writing (Version 1.6.1, July 1999), the known requirements are:

    All |  | Must have 'free',
    Anything that reads from the context |  | Must have 'getC' and 'getBuf',
    Anything that writes to the context |  | Must have 'putC' and 'putBuf'.
    If gdCreateFromGd2Part is called |  | Must also have 'seek' and 'tell'.
    If gdImageGd2 is called |  | Must also have 'seek' and 'tell'.

    ### Please tell us you're using gd!

    When you contact us and let us know you are using gd, you help us justify the time spent in maintaining and improving it. So please let us know. If the results are publicly visible on the web, a URL is a wonderful thing to receive, but if it's not a publicly visible project, a simple note is just as welcome.

    ### If you have problems

    If you have any difficulties with gd, feel free to contact the author, Thomas Boutell. Problems relating to the gd2 format should be addressed to Philip Warner.

    Be sure to read this manual carefully first.

    ### Alphabetical quick index

    gdBrushed | gdDashSize | gdFont | gdFontPtr | gdFree | gdImage | gdImageAlphaBlending | gdImageArc | gdImageBlue | gdImageBoundsSafe | gdImageChar | gdImageCharUp | gdImageColorAllocate | gdImageColorAllocateAlpha | gdImageColorClosest | gdImageColorClosestAlpha | gdImageColorDeallocate | gdImageColorExact | gdImageColorExactAlpha | gdImageColorResolve | gdImageColorResolveAlpha | gdImageColorTransparent | gdImageCopy | gdImageCopyMerge | gdImageMergeGray | gdImageCopyResized | gdImageCopyResampled | gdImageCreate | gdImageCreatePalette | gdImageCreateTrueColor | gdImageCreateFromGd | gdImageCreateFromGd2 | gdImageCreateFromGd2Part | gdImageCreateFromJpeg | gdImageCreateFromPng | gdImageCreateFromPngSource | gdImageCreateFromXbm | gdImageCreateFromXpm | gdImageDashedLine | gdImageDestroy | gdImageFill | gdImageFilledArc | gdImageFilledEllipse | gdImageFillToBorder | gdImageFilledRectangle | gdImageGd | gdImageGd2 | gdImageGetInterlaced | gdImageGetPixel | gdImageGetTransparent | gdImageGreen | gdImageInterlace | gdImageJpeg | gdImageLine | gdImageFilledPolygon | gdImagePaletteCopy | gdImagePng | gdImagePngToSink | gdImagePolygon | gdImagePtr | gdImageWBMP | gdImageRectangle | gdImageRed | gdImageSetBrush | gdImageSetPixel | gdImageSetStyle | gdImageSetTile | gdImageString | gdImageString16 | gdImageStringFT | gdImageStringTTF | gdImageStringUp | gdImageStringUp16 | gdImageWBMP | gdMaxColors | gdPoint | gdStyled | gdStyledBrushed | gdTiled | gdTransparent

    Boutell.Com, Inc.