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SDL_Event(3)				SDL API Reference			     SDL_Event(3)

       SDL_Event- General event structure

       typedef union{
	 Uint8 type;
	 SDL_ActiveEvent active;
	 SDL_KeyboardEvent key;
	 SDL_MouseMotionEvent motion;
	 SDL_MouseButtonEvent button;
	 SDL_JoyAxisEvent jaxis;
	 SDL_JoyBallEvent jball;
	 SDL_JoyHatEvent jhat;
	 SDL_JoyButtonEvent jbutton;
	 SDL_ResizeEvent resize;
	 SDL_ExposeEvent expose;
	 SDL_QuitEvent quit;
	 SDL_UserEvent user;
	 SDL_SywWMEvent syswm;
       } SDL_Event;

       type		   The type of event

       active		   Activation event

       key		   Keyboard event

       motion		   Mouse motion event

       button		   Mouse button event

       jaxis		   Joystick axis motion event

       jball		   Joystick trackball motion event

       jhat		   Joystick hat motion event

       jbutton		   Joystick button event

       resize		   Application window resize event

       expose		   Application window expose event

       quit		   Application quit request event

       user		   User defined event

       syswm		   Undefined window manager event

       The SDL_Event union is the core to all event handling is SDL, its probably the most impor-
       tant structure after SDL_Surface. SDL_Event is a union of all  event  structures  used  in
       SDL,  using  it	is  a  simple matter of knowing which union member relates to which event

       Event type	   Event Structure

       SDL_ACTIVEEVENT	   SDL_ActiveEvent

       SDL_KEYDOWN/UP	   SDL_KeyboardEvent

       SDL_MOUSEMOTION	   SDL_MouseMotionEvent




       SDL_JOYHATMOTION    SDL_JoyHatEvent


       SDL_QUIT 	   SDL_QuitEvent


       SDL_VIDEORESIZE	   SDL_ResizeEvent

       SDL_VIDEOEXPOSE	   SDL_ExposeEvent

       SDL_USEREVENT	   SDL_UserEvent

       The SDL_Event structure has two uses

	  o  Reading events on the event queue

	  o  Placing events on the event queue

       Reading events from the event queue is done with either SDL_PollEvent  or  SDL_PeepEvents.
       We'll use SDL_PollEvent and step through an example.

       First off, we create an empty SDL_Event structure.

       SDL_Event test_event;

	SDL_PollEvent  removes the next event from the event queue, if there are no events on the
       queue it returns 0 otherwise it returns 1. We use a while loop to process  each	event  in

       while(SDL_PollEvent(&test_event)) {

	The  SDL_PollEvent function take a pointer to an SDL_Event structure that is to be filled
       with event information. We know that if SDL_PollEvent removes an event from the queue then
       the  event  information	will be placed in our test_event structure, but we also know that
       the type of event will be placed in the type member of test_event. So to handle each event
       type seperately we use a switch statement.

	 switch(test_event.type) {

	We  need  to  know  what  kind	of events we're looking for and the event type's of those
       events. So lets assume we want to detect where the user is moving the mouse pointer within
       our  application. We look through our event types and notice that SDL_MOUSEMOTION is, more
       than likely, the event we're looking for. A little more research tells use that SDL_MOUSE-
       MOTION  events  are  handled within the SDL_MouseMotionEvent structure which is the motion
       member of SDL_Event. We can check for the SDL_MOUSEMOTION event	type  within  our  switch
       statement like so:


	All we need do now is read the information out of the motion member of test_event.

	     printf("We got a motion event.
	     printf("Current mouse position is: (%d, %d)
       ", test_event.motion.x, test_event.motion.y);
	     printf("Unhandled Event!
       printf("Event queue empty.

       It  is also possible to push events onto the event queue and so use it as a two-way commu-
       nication path. Both SDL_PushEvent and SDL_PeepEvents allow you to place	events	onto  the
       event queue. This is usually used to place a SDL_USEREVENT on the event queue, however you
       could use it to post fake input events if you wished. Creating your own events is a simple
       matter of choosing the event type you want, setting the type member and filling the appro-
       priate member structure with information.

       SDL_Event user_event;


       SDL_PollEvent, SDL_PushEvent, SDL_PeepEvents

SDL				      Tue 11 Sep 2001, 22:59			     SDL_Event(3)
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