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

       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

          •  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  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_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 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