| .TH "SDL_Event" "3" "Tue 11 Sep 2001, 22:59" "SDL" "SDL API Reference" |
| .SH "NAME" |
| SDL_Event \- General event structure |
| .SH "STRUCTURE DEFINITION" |
| .PP |
| .nf |
| \f(CWtypedef 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;\fR |
| .fi |
| .PP |
| .SH "STRUCTURE DATA" |
| .TP 20 |
| \fBtype\fR |
| The type of event |
| .TP 20 |
| \fBactive\fR |
| \fIActivation event\fR |
| .TP 20 |
| \fBkey\fR |
| \fIKeyboard event\fR |
| .TP 20 |
| \fBmotion\fR |
| \fIMouse motion event\fR |
| .TP 20 |
| \fBbutton\fR |
| \fIMouse button event\fR |
| .TP 20 |
| \fBjaxis\fR |
| \fIJoystick axis motion event\fR |
| .TP 20 |
| \fBjball\fR |
| \fIJoystick trackball motion event\fR |
| .TP 20 |
| \fBjhat\fR |
| \fIJoystick hat motion event\fR |
| .TP 20 |
| \fBjbutton\fR |
| \fIJoystick button event\fR |
| .TP 20 |
| \fBresize\fR |
| \fIApplication window resize event\fR |
| .TP 20 |
| \fBexpose\fR |
| \fIApplication window expose event\fR |
| .TP 20 |
| \fBquit\fR |
| \fIApplication quit request event\fR |
| .TP 20 |
| \fBuser\fR |
| \fIUser defined event\fR |
| .TP 20 |
| \fBsyswm\fR |
| \fIUndefined window manager event\fR |
| .SH "DESCRIPTION" |
| .PP |
| The \fBSDL_Event\fR union is the core to all event handling is SDL, its probably the most important structure after \fBSDL_Surface\fR\&. \fBSDL_Event\fR 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 \fBtype\fR\&. |
| .PP |
| .TP 20 |
| \fBEvent \fBtype\fR\fR |
| \fBEvent Structure\fR |
| .TP 20 |
| \fBSDL_ACTIVEEVENT\fP |
| \fI\fBSDL_ActiveEvent\fR\fR |
| .TP 20 |
| \fBSDL_KEYDOWN/UP\fP |
| \fI\fBSDL_KeyboardEvent\fR\fR |
| .TP 20 |
| \fBSDL_MOUSEMOTION\fP |
| \fI\fBSDL_MouseMotionEvent\fR\fR |
| .TP 20 |
| \fBSDL_MOUSEBUTTONDOWN/UP\fP |
| \fI\fBSDL_MouseButtonEvent\fR\fR |
| .TP 20 |
| \fBSDL_JOYAXISMOTION\fP |
| \fI\fBSDL_JoyAxisEvent\fR\fR |
| .TP 20 |
| \fBSDL_JOYBALLMOTION\fP |
| \fI\fBSDL_JoyBallEvent\fR\fR |
| .TP 20 |
| \fBSDL_JOYHATMOTION\fP |
| \fI\fBSDL_JoyHatEvent\fR\fR |
| .TP 20 |
| \fBSDL_JOYBUTTONDOWN/UP\fP |
| \fI\fBSDL_JoyButtonEvent\fR\fR |
| .TP 20 |
| \fBSDL_QUIT\fP |
| \fI\fBSDL_QuitEvent\fR\fR |
| .TP 20 |
| \fBSDL_SYSWMEVENT\fP |
| \fI\fBSDL_SysWMEvent\fR\fR |
| .TP 20 |
| \fBSDL_VIDEORESIZE\fP |
| \fI\fBSDL_ResizeEvent\fR\fR |
| .TP 20 |
| \fBSDL_VIDEOEXPOSE\fP |
| \fI\fBSDL_ExposeEvent\fR\fR |
| .TP 20 |
| \fBSDL_USEREVENT\fP |
| \fI\fBSDL_UserEvent\fR\fR |
| .SH "USE" |
| .PP |
| The \fBSDL_Event\fR structure has two uses |
| .IP " \(bu" 6 |
| Reading events on the event queue |
| .IP " \(bu" 6 |
| Placing events on the event queue |
| .PP |
| Reading events from the event queue is done with either \fI\fBSDL_PollEvent\fP\fR or \fI\fBSDL_PeepEvents\fP\fR\&. We\&'ll use \fBSDL_PollEvent\fP and step through an example\&. |
| .PP |
| First off, we create an empty \fBSDL_Event\fR structure\&. |
| .PP |
| .nf |
| \f(CWSDL_Event test_event;\fR |
| .fi |
| .PP |
| \fBSDL_PollEvent\fP removes the next event from the event queue, if there are no events on the queue it returns \fB0\fR otherwise it returns \fB1\fR\&. We use a \fBwhile\fP loop to process each event in turn\&. |
| .PP |
| .nf |
| \f(CWwhile(SDL_PollEvent(&test_event)) {\fR |
| .fi |
| .PP |
| The \fBSDL_PollEvent\fP function take a pointer to an \fBSDL_Event\fR structure that is to be filled with event information\&. We know that if \fBSDL_PollEvent\fP removes an event from the queue then the event information will be placed in our \fBtest_event\fR structure, but we also know that the \fItype\fP of event will be placed in the \fBtype\fR member of \fBtest_event\fR\&. So to handle each event \fBtype\fR seperately we use a \fBswitch\fP statement\&. |
| .PP |
| .nf |
| \f(CW switch(test_event\&.type) {\fR |
| .fi |
| .PP |
| We need to know what kind of events we\&'re looking for \fIand\fP the event \fBtype\fR\&'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 \fBSDL_MOUSEMOTION\fP is, more than likely, the event we\&'re looking for\&. A little \fImore\fR research tells use that \fBSDL_MOUSEMOTION\fP events are handled within the \fI\fBSDL_MouseMotionEvent\fR\fR structure which is the \fBmotion\fR member of \fBSDL_Event\fR\&. We can check for the \fBSDL_MOUSEMOTION\fP event \fBtype\fR within our \fBswitch\fP statement like so: |
| .PP |
| .nf |
| \f(CW case SDL_MOUSEMOTION:\fR |
| .fi |
| .PP |
| All we need do now is read the information out of the \fBmotion\fR member of \fBtest_event\fR\&. |
| .PP |
| .nf |
| \f(CW 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\&. |
| ");\fR |
| .fi |
| .PP |
| .PP |
| It is also possible to push events onto the event queue and so use it as a two-way communication path\&. Both \fI\fBSDL_PushEvent\fP\fR and \fI\fBSDL_PeepEvents\fP\fR allow you to place events onto the event queue\&. This is usually used to place a \fBSDL_USEREVENT\fP 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 \fBtype\fR member and filling the appropriate member structure with information\&. |
| .PP |
| .nf |
| \f(CWSDL_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);\fR |
| .fi |
| .PP |
| .SH "SEE ALSO" |
| .PP |
| \fI\fBSDL_PollEvent\fP\fR, \fI\fBSDL_PushEvent\fP\fR, \fI\fBSDL_PeepEvents\fP\fR |
| .\" created by instant / docbook-to-man, Tue 11 Sep 2001, 22:59 |