# F - Operating System Issues

This appendix describes the X and WIN32 specific interfaces in FLTK.

## X-Specific Interface

    #include <FL/x.H>

On X you can include this file to access FLTK's X-specific functions. Be warned that some of the structures and calls in it are subject to change in future version of FLTK. Try to avoid doing this so your code is portable.

### Handling Other X Events

#### void Fl::add_handler(int (*f)(int))

Installs a function to parse unrecognized events. If FLTK cannot figure out what to do with an event, it calls each of these functions (most recent first) until one of them returns non-zero. If none of them returns non-zero then the event is ignored.

FLTK calls this for any X events it does not recognize, or X events with a window id that FLTK does not recognize. You can look at the X event with the `fl_xevent` variable.

The argument is zero for unrecognized X events. These handlers are also called for global shortcuts and some other events that the widget they were passed to did not handle. In this case the argument is non-zero (for example `FL_SHORTCUT`).

#### extern XEvent *fl_xvent

The most recent X event.

#### extern ulong fl_event_time

This is the time stamp from the most recent X event that reported it (not all do). Many X calls (like cut and paste) need this value.

#### Window fl_xid(const Fl_Window *)

Returns the XID for a window, or zero if not `shown()`.

#### Fl_Window *fl_find(ulong xid)

Returns the `Fl_Window` that corresponds to the given XID, or `NULL` if not found. This uses a cache so it is slightly faster than iterating through the windows yourself.

#### int fl_handle(const XEvent &)

This call allows you to supply the X events to FLTK, which may allow FLTK to cooperate with another toolkit or library. The return value is true if FLTK understood the event (if the window does not belong to FLTK and the `add_handler()` functions all ignore it this returns false).

Besides feeding events your code should call `Fl::flush()` periodically so that FLTK redraws its windows.

This function will call the callback functions. It will not return until they complete. In particular if a callback pops up a modal window (by calling `fl_ask()`, for instance) it will not return until the modal function returns.

### Drawing using Xlib

The following global variables are set before `Fl_Widget::draw()` is called, or by `Fl_Window::make_current()`:

    extern Display *fl_display;
    extern Window fl_window;
    extern GC fl_gc;
    extern int fl_screen;
    extern XVisualInfo *fl_visual;
    extern Colormap fl_colormap;

You must use them to produce Xlib calls. Don't attempt to change them. A typical X drawing call is written like this:

    XDrawSomething(fl_display, fl_window, fl_gc, ...);

Other information such as the position or size of the X window can be found by looking at `Fl_Window::current()`, which returns a pointer to the `Fl_Window` being drawn.

#### unsigned long fl_xpixel(Fl_Color i)
unsigned long fl_xpixel(uchar r, uchar g, uchar b)

Returns the X pixel number used to draw the given FLTK color index or RGB color. This is the X pixel that `fl_color()` would use.

#### extern XFontStruct *fl_xfont

Points at the font selected by the most recent `fl_font()`. This is not necessarily the current font of `fl_gc`, which is not set until `fl_draw()` is called.

### Changing the Display, Screen, or X Visual

FLTK uses only a single display, screen, X visual, and X colormap. This greatly simplifies its internal structure and makes it much smaller and faster. You can change which it uses by setting global variables before the first `Fl_Window::show()` is called. You may also want to call Fl::visual() , which is a portable interface to get a full color and/or double buffered visual.

#### int Fl::display(const char *)

Set which X display to use. This actually does `putenv("DISPLAY=...")` so that child programs will display on the same screen if called with `exec()`. This must be done before the display is opened. This call is provided under WIN32 but it has no effect.

#### extern Display *fl_display

The open X display. This is needed as an argument to most Xlib calls. Don't attempt to change it! This is `NULL` before the display is opened.

#### void fl_open_display()

Opens the display. Does nothing if it is already open. This will make sure `fl_display` is non-zero. You should call this if you wish to do X calls and there is a chance that your code will be called before the first `show()` of a window.

This may call `Fl::abort()` if there is an error opening the display.

#### void fl_close_display()

This closes the X connection. You do not need to call this to exit, and in fact it is faster to not do so! It may be useful to call this if you want your program to continue without the X connection. You cannot open the display again, and probably cannot call any FLTK functions.

#### extern int fl_screen

Which screen number to use. This is set by `fl_open_display()` to the default screen. You can change it by setting this to a different value immediately afterwards. It can also be set by changing the last number in the `Fl::display()` string to "host:0,#".

#### extern XVisualInfo *fl_visual
extern Colormap fl_colormap

The visual and colormap that FLTK will use for all windows. These are set by `fl_open_display()` to the default visual and colormap. You can change them before calling `show()` on the first window. Typical code for changing the default visual is:

    Fl::args(argc, argv); // do this first so $DISPLAY is set
    fl_open_display();
    fl_visual = find_a_good_visual(fl_display, fl_screen);
    if (!fl_visual) Fl::abort("No good visual");
    fl_colormap = make_a_colormap(fl_display, fl_visual->visual, fl_visual->depth);
    // it is now ok to show() windows:
    window->show(argc, argv);

### Using a Subclass of Fl_Window for Special X Stuff

FLTK can manage an X window on a different screen, visual and/or colormap, you just can't use FLTK's drawing routines to draw into it. But you can write your own `draw()` method that uses Xlib (and/or OpenGL) calls only.

FLTK can also manage XID's provided by other libraries or programs, and call those libraries when the window needs to be redrawn.

To do this, you need to make a subclass of `Fl_Window` and override some of these virtual functions:

#### virtual void Fl_Window::show()

If the window is already `shown()` this must cause it to be raised, this can usually be done by calling `Fl_Window::show()`. If not `shown()` your implementation must call either `Fl_X::set_xid()` or `Fl_X::make_xid()`.

An example:

    void MyWindow::show() {
      if (shown()) {Fl_Window::show(); return;}  // you must do this!
      fl_open_display();	// necessary if this is first window
      // we only calcualte the necessary visual colormap once:
      static XVisualInfo *visual;
      static Colormap colormap;
      if (!visual) {
        visual = figure_out_visual();
        colormap = XCreateColormap(fl_display, RootWindow(fl_display,fl_screen),
    			        vis->visual, AllocNone);
      }
      Fl_X::make_xid(this, visual, colormap);
    }

#### Fl_X *Fl_X::set_xid(Fl_Window *, Window xid)

Allocate a hidden structure called an `Fl_X`, put the XID into it, and set a pointer to it from the `Fl_Window`. This causes `Fl_Window::shown()` to return true.

#### void Fl_X::make_xid(Fl_Window *, XVisualInfo *= fl_visual, Colormap = fl_colormap)

This static method does the most onerous parts of creating an X window, including setting the label, resize limitations, etc. It then does `Fl_X::set_xid()` with this new window and maps the window.

#### virtual void Fl_Window::flush()

This virtual function is called by `Fl::flush()` to update the window. For FLTK's own windows it does this by setting the global variables `fl_window` and `fl_gc` and then calling the `draw()` method. For your own windows you might just want to put all the drawing code in here.

The X region that is a combination of all `damage()` calls done so far is in `Fl_X::i(this)->region`. If `NULL` then you should redraw the entire window. The undocumented function `fl_clip_region(XRegion)` will initialize the FLTK clip stack with a region or `NULL` for no clipping. You must set region to `NULL` afterwards as `fl_clip_region()` now owns it and will delete it when done.

If `damage() FL_DAMAGE_EXPOSE` then only X expose events have happened. This may be useful if you have an undamaged image (such as a backing buffer) around.

Here is a sample where an undamaged image is kept somewhere:

    void MyWindow::flush() {
      fl_clip_region(Fl_X::i(this)->region);
      Fl_X::i(this)->region = 0;
      if (damage() != 2) {... draw things into backing store ...}
      ... copy backing store to window ...
    }

#### virtual void Fl_Window::hide()

Destroy the window server copy of the window. Usually you will destroy contexts, pixmaps, or other resources used by the window, and then call `Fl_Window::hide()` to get rid of the main window identified by `xid()`. If you override this, you must also override the destructor as shown:

    void MyWindow::hide() {
      if (mypixmap) {
        XFreePixmap(fl_display,mypixmap);
        mypixmap = 0;
      }
      Fl_Window::hide(); // you must call this
    }

#### virtual void Fl_Window::~Fl_Window()

Because of the way C++ works, if you override `hide()` you must override the destructor as well (otherwise only the base class `hide()` is called):

    MyWindow::~MyWindow() {
      hide();
    }

### Setting the Icon of a Window

FLTK currently supports setting a window's icon *before* it is shown using the `Fl_Window::icon()` method.

#### void Fl_Window::icon(char *)

Sets the icon for the window to the passed pointer. You will need to cast the icon `Pixmap` to a `char *` when calling this method. To set the icon using a bitmap compiled with your application use:

    #include "icon.xbm"

    Pixmap p = XCreateBitmapFromData(fl_display, DefaultRootWindow(fl_display),
                                     icon_bits, icon_width, icon_height);

    window->icon((char *)p);

Note: you must call `Fl_Window::show(argc, argv)` for the icon to be used. The `Fl_Window::show()` method does not bind the icon to the window.

## WIN32-Specific Interface

    #include <FL/x.H>

The `<FL/x.H>` header file defines the interface to FLTK's WIN32-specific functions. Be warned that some of the structures and calls in it are subject to change in future version of FLTK. Try to avoid doing this so your code is portable.

### Handling Other WIN32 Messages

By default a single WNDCLASSEX called "FLTK" is created. All `Fl_Windows` are of this class unless you use `Fl_Window::xclass()` . The window class is created the first time `Fl_Window::show()` is called.

You can probably combine FLTK with other libraries that make their own WIN32 window classes. The easiest way is to call `Fl::wait()` , it will call `DispatchMessage` for all messages to the other windows. If necessary you can let the other library take over (as long as it calls `DispatchMessage()`), but you will have to arrange for the function `Fl::flush()` to be called regularily so that widgets are updated, timeouts are handled, and the idle functions are called.

#### extern MSG fl_msg

The most recent message read by `GetMessage` (which is called by `Fl::wait()`. This may not be the most recent message sent to an FLTK window, because silly WIN32 calls the handle procedures directly for some events (sigh).

#### void Fl::add_handler(int (*f)(int))

Install a function to parse unrecognized messages sent to FLTK windows. If FLTK cannot figure out what to do with a message, it calls each of these functions (most recent first) until one of them returns non-zero. The argument passed to the fuctions is zero. If all the handlers return zero then FLTK calls `DefWindowProc()`.

#### HWND fl_xid(const Fl_Window *)

Returns the window handle for a `Fl_Window`, or zero if not `shown()`.

#### Fl_Window *fl_find(HWND xid)

Return the `Fl_Window` that corresponds to the given window handle, or `NULL` if not found. This uses a cache so it is slightly faster than iterating through the windows yourself.

### Drawing Things Using the WIN32 GDI

When the virtual function `Fl_Widget::draw()` is called, FLTK has stashed in some global variables all the silly extra arguments you need to make a proper GDI call. These are:

    extern HINSTANCE fl_display;
    extern HWND fl_window;
    extern HDC fl_gc;
    COLORREF fl_RGB();
    HPEN fl_pen();
    HBRUSH fl_brush();

These global variables are set before `draw()` is called, or by `Fl_Window::make_current()` . You can refer to them when needed to produce GDI calls. Don't attempt to change them. The functions return GDI objects for the current color set by `fl_color()` and are created as needed and cached. A typical GDI drawing call is written like this:

    DrawSomething(fl_gc, ..., fl_brush());

It may also be useful to refer to `Fl_Window::current()` to get the window's size or position.

### Setting the Icon of a Window

FLTK currently supports setting a window's icon *before* it is shown using the `Fl_Window::icon()` method.

#### void Fl_Window::icon(char *)

Sets the icon for the window to the passed pointer. You will need to cast the `HICON` handle to a `char *` when calling this method. To set the icon using an icon resource compiled with your application use:

    window->icon((char *)LoadIcon(fl_display, MAKEINTRESOURCE(IDI_ICON)));

You can also use the `LoadImage()` and related functions to load specific resolutions or create the icon from bitmap data.

Note: you must call `Fl_Window::show(argc, argv)` for the icon to be used. The `Fl_Window::show()` method does not bind the icon to the window.

### How to Not Get a MSDOS Console Window

WIN32 has a really stupid mode switch stored in the executables that controls whether or not to make a console window.

To always get a console window you simply create a console application (the "/SUBSYSTEM:CONSOLE" option for the linker). For a GUI-only application create a WIN32 application (the "/SUBSYSTEM:WINDOWS" option for the linker).

FLTK includes a `WinMain()` function that calls the ANSI standard `main()` entry point for you. This function creates a console window when you use the debug version of the library.

WIN32 applications without a console cannot write to `stdout` or `stderr`, even if they are run from a console window. Any output is silently thrown away.

### Known Bugs

If a program is deactivated, `Fl::wait()` does not return until it is activated again, even though many events are delivered to the program. This can cause idle background processes to stop unexpectedly. This also happens while the user is dragging or resizing windows or otherwise holding the mouse down. I was forced to remove most of the efficiency FLTK uses for redrawing in order to get windows to update while being moved. This is a design error in WIN32 and probably impossible to get around.

`Fl_Gl_Window::can_do_overlay()` returns true until the first time it attempts to draw an overlay, and then correctly returns whether or not there is overlay hardware.

Cut text contains ^J rather than ^M^J to break lines. This is a feature, not a bug.

`SetCapture` (used by `Fl::grab()`) doesn't work, and the main window title bar turns gray while menus are popped up.

FLUID does not support BMP files yet.