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

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