SDL_Event

SDL_Event

NAME STRUCTURE DEFINITION STRUCTURE DATA DESCRIPTION USE SEE ALSO

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_!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

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_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( 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(

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(

SEE ALSO

SDL_!PollEvent, SDL_!PushEvent, SDL_!PeepEvents