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Updated: Thursday, June 13, 2019
 
 

SDL_Event (3)

Name

SDL_Event - General event structure

Synopsis

Please see following description for synopsis

Description

SDL_Event(3)                   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
       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_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;

        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:

           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);

ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | library/sdl      |
       +---------------+------------------+
       |Stability      | Volatile         |
       +---------------+------------------+
SEE ALSO
       SDL_PollEvent, SDL_PushEvent, SDL_PeepEvents



NOTES
       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source       was        downloaded        from         https://www.lib-
       sdl.org/release/SDL-1.2.15.tar.gz

       Further information about this software can be found on the open source
       community website at https://www.libsdl.org/.



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