| DRAW(3) | DRAW(3)

NAME

Image, draw, drawop, gendraw, gendrawop, drawreplxy, drawrepl, replclipr, line, lineop, poly, polyop, fillpoly, fillpolyop, bezier, bezierop, bezspline, bezsplineop, bezsplinepts, fillbezier, fillbezierop, fillbezspline, fillbezsplineop, ellipse, ellipseop, fillellipse, fillellipseop, arc, arcop, fillarc, fillarcop, icossin, icossin2, border, string, stringop, stringn, stringnop, runestring, runestringop, runestringn, runestringnop, stringbg, stringbgop, stringnbg, stringnbgop, runestringbg, runestringbgop, runestringnbg, runestringnbgop, _string, ARROW, drawsetdebug – graphics functions

SYNOPSIS

`#include <u.h>
#include <libc.h>
#include <draw.h>

typedef
struct Image
{

Display *display; /* display holding data */
int id; /* id of system−held Image */
Rectangle r; /* rectangle in data area, local coords */
Rectangle clipr; /* clipping region */
ulong chan; /* pixel channel format descriptor */
int depth; /* number of bits per pixel */
int repl; /* flag: data replicates to tile clipr */
Screen *screen; /* 0 if not a window */
Image *next; /* next in list of windows */

} Image;

typedef enum
{

| /* Porter−Duff compositing operators */ Clear = 0, SinD = 8, DinS = 4, SoutD = 2, DoutS = 1, S = SinD|SoutD, SoverD = SinD|SoutD|DoutS, SatopD = SinD|DoutS, SxorD = SoutD|DoutS, D = DinS|DoutS, DoverS = DinS|DoutS|SoutD, DatopS = DinS|SoutD, DxorS = DoutS|SoutD, /* == SxorD */ Ncomp = 12,

} Drawop;

void draw(Image *dst, Rectangle r, Image *src,

Image *mask, Point p)

void drawop(Image *dst, Rectangle r, Image *src,

Image *mask, Point p, Drawop op)

void gendraw(Image *dst, Rectangle r, Image *src, Point sp,

Image *mask, Point mp)

void gendrawop(Image *dst, Rectangle r, Image *src, Point sp,

Image *mask, Point mp, Drawop op)

int drawreplxy(int min, int max, int x)

Point drawrepl(Rectangle r, Point p)

void replclipr(Image *i, int repl, Rectangle clipr)

void line(Image *dst, Point p0, Point p1, int end0, int end1,

int radius, Image *src, Point sp)

void lineop(Image *dst, Point p0, Point p1, int end0, int end1,

int radius, Image *src, Point sp, Drawop op)

void poly(Image *dst, Point *p, int np, int end0, int end1,

int radius, Image *src, Point sp)

void polyop(Image *dst, Point *p, int np, int end0, int end1,

int radius, Image *src, Point sp, Drawop op)

void fillpoly(Image *dst, Point *p, int np, int wind,

Image *src, Point sp)

void fillpolyop(Image *dst, Point *p, int np, int wind,

Image *src, Point sp, Drawop op)

int bezier(Image *dst, Point p0, Point p1, Point p2, Point p3,

int end0, int end1, int radius, Image *src, Point sp)

int bezierop(Image *dst, Point p0, Point p1, Point p2, Point p3,

int end0, int end1, int radius, Image *src, Point sp,
Drawop op)

int bezspline(Image *dst, Point *pt, int npt, int end0, int end1,

int radius, Image *src, Point sp)

int bezsplineop(Image *dst, Point *pt, int npt, int end0, int end1,

int radius, Image *src, Point sp, Drawop op)

int bezsplinepts(Point *pt, int npt, Point **pp)

int fillbezier(Image *dst, Point p0, Point p1, Point p2, Point p3,

int w, Image *src, Point sp)

int fillbezierop(Image *dst, Point p0, Point p1, Point p2, Point p3,

int w, Image *src, Point sp, Drawop op)

int fillbezspline(Image *dst, Point *pt, int npt, int w,

Image *src, Point sp)

int fillbezsplineop(Image *dst, Point *pt, int npt, int w,

Image *src, Point sp, Drawop op)

void ellipse(Image *dst, Point c, int a, int b, int thick,

Image *src, Point sp)

void ellipseop(Image *dst, Point c, int a, int b, int thick,

Image *src, Point sp, Drawop op)

void fillellipse(Image *dst, Point c, int a, int b,

Image *src, Point sp)

void fillellipseop(Image *dst, Point c, int a, int b,

Image *src, Point sp, Drawop op)

void arc(Image *dst, Point c, int a, int b, int thick,

Image *src, Point sp, int alpha, int phi)

void arcop(Image *dst, Point c, int a, int b, int thick,

Image *src, Point sp, int alpha, int phi, Drawop op)

void fillarc(Image *dst, Point c, int a, int b, Image *src,

Point sp, int alpha, int phi)

void fillarcop(Image *dst, Point c, int a, int b, Image *src,

Point sp, int alpha, int phi, Drawop op)

int icossin(int deg, int *cosp, int *sinp)

int icossin2(int x, int y, int *cosp, int *sinp)

void border(Image *dst, Rectangle r, int i, Image *color, Point sp)

Point string(Image *dst, Point p, Image *src, Point sp,

Font *f, char *s)

Point stringop(Image *dst, Point p, Image *src, Point sp,

Font *f, char *s, Drawop op)

Point stringn(Image *dst, Point p, Image *src, Point sp,

Font *f, char *s, int len)

Point stringnop(Image *dst, Point p, Image *src, Point sp,

Font *f, char *s, int len, Drawop op)

Point runestring(Image *dst, Point p, Image *src, Point sp,

Font *f, Rune *r)

Point runestringop(Image *dst, Point p, Image *src, Point sp,

Font *f, Rune *r, Drawop op)

Point runestringn(Image *dst, Point p, Image *src, Point sp,

Font *f, Rune *r, int len)

Point runestringnop(Image *dst, Point p, Image *src, Point sp,

Font *f, Rune *r, int len, Drawop op)

Point stringbg(Image *dst, Point p, Image *src, Point sp,

Font *f, char *s, Image *bg, Point bgp)

Point stringbgop(Image *dst, Point p, Image *src, Point sp,

Font *f, char *s, Image *bg, Point bgp, Drawop op)

Point stringnbg(Image *dst, Point p, Image *src, Point sp,

Font *f, char *s, int len, Image *bg, Point bgp)

Point stringnbgop(Image *dst, Point p, Image *src, Point sp,

Font *f, char *s, int len, Image *bg, Point bgp, Drawop op)

Point runestringbg(Image *dst, Point p, Image *src, Point sp,

Font *f, Rune *r, Image *bg, Point bgp)

Point runestringbgop(Image *dst, Point p, Image *src, Point sp,

Font *f, Rune *r, Image *bg, Point bgp, Drawop op)

Point runestringnbg(Image *dst, Point p, Image *src, Point sp,

Font *f, Rune *r, int len, Image *bg, Point bgp)

Point runestringnbgop(Image *dst, Point p, Image *src, Point sp,

Font *f, Rune *r, int len, Image *bg, Point bgp, Drawop op)

Point _string(Image *dst, Point p, Image *src,

Point sp, Font *f, char *s, Rune *r, int len,
Rectangle clipr, Image *bg, Point bgp, Drawop op)

void drawsetdebug(int on)

enum
{

| /* line ends */ Endsquare = 0, Enddisc = 1, Endarrow = 2, Endmask = 0x1F

};

#define ARROW(a, b, c) (Endarrow|((a)<<5)|((b)<<14)|((c)<<23))
`

DESCRIPTION

The `Image` type defines rectangular pictures and the methods to draw upon them; it is also the building block for higher level objects such as windows and fonts. In particular, a window is represented as an `Image`; no special operators are needed to draw on a window.

`r` The coordinates of the rectangle in the plane for which the `Image` has defined pixel values. It should not be modified after the image is created.
`clipr` The clipping rectangle: operations that read or write the image will not access pixels outside `clipr`. Frequently, `clipr` is the same as `r`, but it may differ; see in particular the discussion of `repl`. The clipping region may be modified dynamically using replclipr (q.v.).
`chan` The pixel channel format descriptor, as described in image(7). The value should not be modified after the image is created.
`depth` The number of bits per pixel in the picture; it is identically `chantodepth(chan)` (see graphics(3)) and is provided as a convenience. The value should not be modified after the image is created.
`repl` A boolean value specifying whether the image is tiled to cover the plane when used as a source for a drawing operation. If `repl` is zero, operations are restricted to the intersection of `r` and `clipr`. If `repl` is set, `r` defines the tile to be replicated and `clipr` defines the portion of the plane covered by the tiling, in other words, `r` is replicated

to cover `clipr`; in such cases `r` and `clipr` are independent.
For example, a replicated image with `r` set to ((0, 0), (1, 1)) and `clipr` set to ((0, 0), (100, 100)), with the single pixel of `r` set to blue, behaves identically to an image with `r` and `clipr` both set to ((0, 0), (100, 100)) and all pixels set to blue. However, the first image requires far less memory. The replication flag may be modified dynamically using replclipr (q.v.).

Most of the drawing functions come in two forms: a basic form, and an extended form that takes an extra `Drawop` to specify a Porter-Duff compositing operator to use. The basic forms assume the operator is `SoverD`, which suffices for the vast majority of applications. The extended forms are named by adding an -`op` suffix to the basic form. Only the basic forms are listed below.
`draw(`dst`,` r`,` src`,` mask`,` p`)
`

Draw is the standard drawing function. Only those pixels within the intersection of dst`−>r` and dst`−>clipr` will be affected; draw ignores dst`−>repl`. The operation proceeds as follows (this is a description of the behavior, not the implementation):
1. If `repl` is set in src or mask, replicate their contents to fill their clip rectangles.
2. Translate src and mask so p is aligned with r`.min`.
3. Set r to the intersection of r and dst`−>r`.
4. Intersect r with src`−>clipr`. If src`−>repl` is false, also intersect r with src`−>r`.
5. Intersect r with mask`−>clipr`. If mask`−>repl` is false, also intersect r with mask`−>r`.
6. For each location in r, combine the dst pixel with the src pixel using the alpha value corresponding to the mask pixel. If the mask has an explicit alpha channel, the alpha value corresponding to the mask pixel is simply that pixel’s alpha channel. Otherwise, the alpha value is the NTSC greyscale equivalent of the color value, with white

| meaning opaque and black transparent. In terms of the Porter-Duff compositing algebra, draw replaces the dst pixels with (src in mask) over dst. (In the extended form, “over” is replaced by op).

The various pixel channel formats involved need not be identical. If the channels involved are smaller than 8-bits, they will be promoted before the calculation by replicating the extant bits; after the calculation, they will be truncated to their proper sizes.

`gendraw(`dst`,` r`,` src`,` p0`,` mask`,` p1`)
`

| Similar to draw except that gendraw aligns the source and mask differently: src is aligned so p0 corresponds to r`.min` and mask is aligned so p1 corresponds to r`.min`. For most purposes with simple masks and source images, `draw` is sufficient, but `gendraw` is the general operator and the one all other drawing primitives are built upon.

`drawreplxy(`min`,`max`,`x`)
`

| Clips x to be in the half-open interval [min, max) by adding or subtracting a multiple of max-min.

`drawrepl(`r`,`p`)
`

| Clips the point p to be within the rectangle r by translating the point horizontally by an integer multiple of rectangle width and vertically by the height.

`replclipr(`i`,`repl`,`clipr`)
`

| Because the image data is stored on the server, local modifications to the `Image` data structure itself will have no effect. Repclipr modifies the local `Image` data structure’s `repl` and `clipr` fields, and notifies the server of their modification.

`line(`dst`,` p0`,` p1`,` end0`,` end1`,` thick`,` src`,` sp`)
`

Line draws in dst a line of width 1+2*thick pixels joining points p0 and p1. The line is drawn using pixels from the src image aligned so sp in the source corresponds to p0 in the destination. The line touches both p0 and p1, and end0 and end1 specify how the ends of the line are drawn. `Endsquare` terminates the line perpendicularly to the direction of the line; a thick line with `Endsquare` on both ends will be a rectangle. `Enddisc` terminates the line by drawing a disc of diameter 1+2*thick centered on the end point. `Endarrow` terminates the line with an arrowhead whose tip touches the endpoint.
The macro `ARROW` permits explicit control of the shape of the arrow. If all three parameters are zero, it produces the default arrowhead, otherwise, a sets the distance along line from end of the regular line to tip, b sets the distance along line from the barb to the tip, and c sets the distance perpendicular to the line from edge of line to the tip of the barb, all in pixels.
Line and the other geometrical operators are equivalent to calls to gendraw using a mask produced by the geometric procedure.

`poly(`dst`,` p`,` np`,` end0`,` end1`,` thick`,` src`,` sp`)
`

| Poly draws a general polygon; it is conceptually equivalent to a series of calls to line joining adjacent points in the array of `Points` p, which has np elements. The ends of the polygon are specified as in line; interior lines are terminated with `Enddisc` to make smooth joins. The source is aligned so sp corresponds to p`[0]`.

`fillpoly(`dst`,` p`,` np`,` wind`,` src`,` sp`)
`

Fillpoly is like poly but fills in the resulting polygon rather than outlining it. The source is aligned so sp corresponds to p`[0]`. The winding rule parameter wind resolves ambiguities about what to fill if the polygon is self-intersecting. If wind is `~0`, a pixel is inside the polygon if the polygon’s winding number about the point is non-zero. If wind is `1`, a pixel is inside if the winding number is odd. Complementary values (0 or ~1) cause outside pixels to be filled. The meaning of other values is undefined. The polygon is closed with a line if necessary.

`bezier(`dst`,` a`,` b`,` c`,` d`,` end0`,` end1`,` thick`,` src`,` sp`)
`

| Bezier draws the cubic Bezier curve defined by `Points` a, b, c, and d. The end styles are determined by end0 and end1; the thickness of the curve is 1+2*thick. The source is aligned so sp in src corresponds to a in dst.

`bezspline(`dst`,` p`,` end0`,` end1`,` thick`,` src`,` sp`)
`

| Bezspline takes the same arguments as poly but draws a quadratic B-spline (despite its name) rather than a polygon. If the first and last points in p are equal, the spline has periodic end conditions.

`bezsplinepts(`pt`,` npt`,` pp`)
`

| Bezsplinepts returns in pp a list of points making up the open polygon that bezspline would draw. The caller is responsible for freeing *pp.

`fillbezier(`dst`,` a`,` b`,` c`,` d`,` wind`,` src`,` sp`)
`

| Fillbezier is to bezier as fillpoly is to poly.

`fillbezspline(`dst`,` p`,` wind`,` src`,` sp`)
`

| Fillbezspline is like fillpoly but fills the quadratic B-spline rather than the polygon outlined by p. The spline is closed with a line if necessary.

`ellipse(`dst`,` c`,` a`,` b`,` thick`,` src`,` sp`)
`

| Ellipse draws in dst an ellipse centered on c with horizontal and vertical semiaxes a and b. The source is aligned so sp in src corresponds to c in dst. The ellipse is drawn with thickness 1+2*thick.

`fillellipse(`dst`,` c`,` a`,` b`,` src`,` sp`)
`

| Fillellipse is like ellipse but fills the ellipse rather than outlining it.

`arc(`dst`,` c`,` a`,` b`,` thick`,` src`,` sp`,` alpha`,` phi`)
`

| Arc is like ellipse, but draws only that portion of the ellipse starting at angle alpha and extending through an angle of phi. The angles are measured in degrees counterclockwise from the positive x axis.

`fillarc(`dst`,` c`,` a`,` b`,` src`,` sp`,` alpha`,` phi`)
`

| Fillarc is like arc, but fills the sector with the source color.

`icossin(`deg`,` cosp`,` sinp`)
`

| Icossin stores in `*`cosp and `*`sinp scaled integers representing the cosine and sine of the angle deg, measured in integer degrees. The values are scaled so cos(0) is 1024.

`icossin2(`x`,` y`,` cosp`,` sinp`)
`

| Icossin2 is analogous to icossin, with the angle represented not in degrees but implicitly by the point (x,y). It is to icossin what `atan2` is to `atan` (see sin(3)).

`border(`dst`,` r`,` i`,` color`,` sp`)
`

| Border draws an outline of rectangle r in the specified color. The outline has width i; if positive, the border goes inside the rectangle; negative, outside. The source is aligned so sp corresponds to r`.min`.

`string(`dst`,` p`,` src`,` sp`,` font`,` s`)
`

String draws in dst characters specified by the string s and font; it is equivalent to a series of calls to gendraw using source src and masks determined by the character shapes. The text is positioned with the left of the first character at p`.x` and the top of the line of text at p`.y`. The source is positioned so sp in src corresponds to p in dst. String returns a `Point` that is the position of the next character that would be drawn if the string were longer.
For characters with undefined or zero-width images in the font, the character at font position 0 (NUL) is drawn.
The other string routines are variants of this basic form, and have names that encode their variant behavior. Routines whose names contain `rune` accept a string of Runes rather than UTF-encoded bytes. Routines ending in `n` accept an argument, n, that defines the number of characters to draw rather than accepting a NUL-terminated string. Routines containing `bg` draw the background behind the characters in the specified color (bg) and alignment (bgp); normally the text is drawn leaving the background intact.
The routine _string captures all this behavior into a single operator. Whether it draws a UTF string or Rune string depends on whether s or r is null (the string length is always determined by len). If bg is non-null, it is used as a background color. The clipr argument allows further management of clipping when drawing the string; it is intersected with the usual clipping rectangles to further limit the extent of the text.

`drawsetdebug(`on`)
`

| Turns on or off debugging output (usually to a serial line) according to whether on is non-zero.

SOURCE

| `/usr/local/plan9/src/libdraw`

SEE ALSO

graphics(3), stringsize(3), color(7), utf(7), addpt(3)

T. Porter, T. Duff. “Compositing Digital Images”, Computer Graphics (Proc. SIGGRAPH), 18:3, pp. 253-259, 1984.

DIAGNOSTICS

| These routines call the graphics error function on fatal errors.

BUGS

| Anti-aliased characters can be drawn by defining a font with multiple bits per pixel, but there are no anti-aliasing geometric primitives.