|type||The type of 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 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
The SDL_Event structure has two uses
Reading events from the event queue is done with either SDL_PollEvent or SDL_PeepEvents. Well use SDL_PollEvent and step through an example.
o Reading events on the event queue o Placing events on the event queue
First off, we create an empty SDL_Event structure.
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.
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.
We need to know what kind of events were looking for and the event types 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 were 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 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.
user_event.type=SDL_USEREVENT; user_event.user.code=2; user_event.user.data1=NULL; user_event.user.data2=NULL; SDL_PushEvent(&user_event);
SDL_PollEvent, SDL_PushEvent, SDL_PeepEvents
|SDL||SDL_EVENT (3)||Tue 11 Sep 2001, 22:59|