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_SywWMEvent 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
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 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)
