The General Drawing Kit

Version 1.0

May 1996

by Peter Mattis

1. Copying

GDK is free; this means that everyone is free to use it and free to redestribute it on a free basis. GDK is not in the public domain; it is copyrighted and there are restrictions on its distribution, but these restrictions are designed to permit everything that a good cooperating citizen would want to do. What is not allowed is to try to prevent others from further sharing any version of GDK that they might get from you.

Specifically, we want to make sure that you have the right to give away copies of GDK, that you receive source code or else can get it if you want it, that you can change GDK or use pieces of it in new free programs, and that you know you can do these things.

To make sure that everyone has such rights, we have to forbid you to deprive anyone else of these rights. For example, if you distribute copies of GDK, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must tell them their rights.

Also, for my own protection, we must make certain that everyone finds out that there is no warranty for GDK. If GDK is modified by someone else and passed on, we want their recipients to know that what they have is not what we distributed, so that any problems introduced by others will no reflect on our reputation.

The precise conditions of the licenses for GDK are found in the General Public Licenses that accompanies it.

2. What is GDK?

GDK is designed as a wrapper library that lies on top of Xlib. It performs many common and desired operations for a programmer instead of the programmer having to explicitly ask for such functionality from Xlib directly. For example, GDK provides a common interface to both regular and shared memory XImage types. By doing so, an application can nearly transparently use the fastest image type available. GDK also provides routines for determining the best available color depth and the best available visual which is not always the default visual for a screen.

3. Initialization and exit

Initializing GDK is easy. Simply call gdk_init passing in the argc and argv parameters. Exit is similarly easy. Just call gdk_exit.

Function: void gdk_init (int *argc, char ***argv): Initializes the GDK library. The arguments argc and argv are scanned and any arguments that GDK recognizes are handled and removed. The argc and argv parameters are the values passed to main upon program invocation.

Function: void gdk_exit (int errorcode): Exit GDK and perform any necessary cleanup. gdk_exit will call the systems exit function passing errorcode as the parameter.

int
main (int argc, char *argv[])
{
  /* Initialize GDK. */
  gdk_init (&argc, &argv);

  /* Exit from GDK...this call will never return. */
  gdk_exit (0);

  /* Keep compiler from issuing a warning */
  return 0;
}

4. Event handling

Events are the means by which GDK lets the programmer know of user interaction. An event is normally a button or key press or some other indirect user action, such as a the mouse cursor entering or leaving a window.

There exist only a few functions for getting events and event information. These are gdk_events_pending, gdk_event_get, gdk_events_record and gdk_events_playback. The latter two functions are useful for automatic testing of a software package and should normally not be needed in a program.

Function: gint gdk_events_pending (void): Returns the number of events pending on the event queue.

Function: gint gdk_event_get (GdkEvent *event): Return the next available event in the event structure. gdk_event_get will return TRUE on success and FALSE on failure. Success and failure is determined by whether an event arrived before the timeout period expired.

Function: void gdk_events_record (char *filename): Turn on recording of events. User events and certain system events will be saved in the file named by the variable filename. This stream of events can later be played back and "should" produce the same results as when the original events were handled. However, the programmer does need to be careful in that the state of the program must be the same when gdk_events_record is called and when gdk_events_playback is called. For this reason, gdk_events_record is normally not called directly, but is instead invoked indirectly by specifying the "-record" command line option.

Function: void gdk_events_playback (char *filename): Start playback of events from a file. (See the above description of gdk_events_record). Normally this function is not called directly but is invoked by the "-playback" command line option.

Function: void gdk_events_stop (void): Stop recording and playback of events.

void
handle_event ()
{
  GdkEvent event;

  if (gdk_event_get (&event))
    {
      switch (event.type)
       {
         ...
       }
    }
}

5. Understanding and using visuals

6. Creating and using windows

7. Creating and modifying GCs

8. Creating pixmaps

9. Creating images

10. Specifying color

11. Creating Fonts

12. Drawing Commands

13. Using extended devices

14. Other stuff

15. Using GDK

Variable Index

Jump to: g

g

Concept Index

Jump to: c - d - e - f - g - i - m - o - p - t - u - v - w

Exit