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SDL API Reference                                    SDL_Event(3)



NAME
     SDL_Event - General event structure

STRUCTURE DEFINITION
     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;

STRUCTURE DATA
     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

DESCRIPTION




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SDL API Reference                                    SDL_Event(3)



     The SDL_Event union is the core to  all  event  handling  is
     SDL,   its  probably  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_MOUSEBUTTONDOWN/UP
                         SDL_MouseButtonEvent

     SDL_JOYAXISMOTION   SDL_JoyAxisEvent

     SDL_JOYBALLMOTION   SDL_JoyBallEvent

     SDL_JOYHATMOTION    SDL_JoyHatEvent

     SDL_JOYBUTTONDOWN/UP
                         SDL_JoyButtonEvent

     SDL_QUIT            SDL_QuitEvent

     SDL_SYSWMEVENT      SDL_SysWMEvent

     SDL_VIDEORESIZE     SDL_ResizeEvent

     SDL_VIDEOEXPOSE     SDL_ExposeEvent

     SDL_USEREVENT       SDL_UserEvent

USE
     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;





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SDL API Reference                                    SDL_Event(3)



      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 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  look-
     ing   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:

         case SDL_MOUSEMOTION:

      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);
           break;
         default:
           printf("Unhandled Event!
     ");
           break;
       }
     }
     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



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SDL API Reference                                    SDL_Event(3)



     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;

     user_event.type=SDL_USEREVENT;
     user_event.user.code=2;
     user_event.user.data1=NULL;
     user_event.user.data2=NULL;
     SDL_PushEvent(&user_event);

SEE ALSO
     SDL_PollEvent, SDL_PushEvent, SDL_PeepEvents








































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