SDL_Event man page on JazzOS

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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_SysWMEvent 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 prob‐
       ably the most important 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 type.

       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

	  ·  Reading events on the event queue

	  ·  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 turn.

       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 informa‐
       tion 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_MOUSEMOTION	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

	     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 communication 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 appropriate 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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