SDL_Event(3)

1SDL_Event(3)                   SDL API Reference                  SDL_Event(3)
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NAME

6       SDL_Event - General event structure
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STRUCTURE DEFINITION

9       typedef union{
10         Uint8 type;
11         SDL_ActiveEvent active;
12         SDL_KeyboardEvent key;
13         SDL_MouseMotionEvent motion;
14         SDL_MouseButtonEvent button;
15         SDL_JoyAxisEvent jaxis;
16         SDL_JoyBallEvent jball;
17         SDL_JoyHatEvent jhat;
18         SDL_JoyButtonEvent jbutton;
19         SDL_ResizeEvent resize;
20         SDL_ExposeEvent expose;
21         SDL_QuitEvent quit;
22         SDL_UserEvent user;
23         SDL_SysWMEvent syswm;
24       } SDL_Event;
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STRUCTURE DATA

27       type                The type of event
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29       active              Activation event
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31       key                 Keyboard event
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33       motion              Mouse motion event
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35       button              Mouse button event
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37       jaxis               Joystick axis motion event
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39       jball               Joystick trackball motion event
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41       jhat                Joystick hat motion event
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43       jbutton             Joystick button event
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45       resize              Application window resize event
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47       expose              Application window expose event
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49       quit                Application quit request event
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51       user                User defined event
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53       syswm               Undefined window manager event
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DESCRIPTION

56       The SDL_Event union is the core to all event handling is SDL, its prob‐
57       ably the most important structure after  SDL_Surface.  SDL_Event  is  a
58       union  of all event structures used in SDL, using it is a simple matter
59       of knowing which union member relates to which event type.
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61       Event type          Event Structure
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63       SDL_ACTIVEEVENT     SDL_ActiveEvent
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65       SDL_KEYDOWN/UP      SDL_KeyboardEvent
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67       SDL_MOUSEMOTION     SDL_MouseMotionEvent
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69       SDL_MOUSEBUTTONDOWN/UP
70                           SDL_MouseButtonEvent
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72       SDL_JOYAXISMOTION   SDL_JoyAxisEvent
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74       SDL_JOYBALLMOTION   SDL_JoyBallEvent
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76       SDL_JOYHATMOTION    SDL_JoyHatEvent
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78       SDL_JOYBUTTONDOWN/UP
79                           SDL_JoyButtonEvent
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81       SDL_QUIT            SDL_QuitEvent
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83       SDL_SYSWMEVENT      SDL_SysWMEvent
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85       SDL_VIDEORESIZE     SDL_ResizeEvent
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87       SDL_VIDEOEXPOSE     SDL_ExposeEvent
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89       SDL_USEREVENT       SDL_UserEvent
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USE

92       The SDL_Event structure has two uses
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94          ·  Reading events on the event queue
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96          ·  Placing events on the event queue
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98       Reading events from the event queue is done with  either  SDL_PollEvent
99       or SDL_PeepEvents. We'll use SDL_PollEvent and step through an example.
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101       First off, we create an empty SDL_Event structure.
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103       SDL_Event test_event;
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105        SDL_PollEvent  removes  the  next event from the event queue, if there
106       are no events on the queue it returns 0 otherwise it returns 1. We  use
107       a while loop to process each event in turn.
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109       while(SDL_PollEvent(&test_event)) {
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111        The  SDL_PollEvent  function  take a pointer to an SDL_Event structure
112       that  is  to  be  filled  with  event  information.  We  know  that  if
113       SDL_PollEvent  removes  an event from the queue then the event informa‐
114       tion will be placed in our test_event structure, but we also know  that
115       the  type  of event will be placed in the type member of test_event. So
116       to handle each event type seperately we use a switch statement.
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118         switch(test_event.type) {
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120        We need to know what kind of events we're looking for  and  the  event
121       type's of those events. So lets assume we want to detect where the user
122       is moving the mouse pointer within our application. We look through our
123       event  types  and notice that SDL_MOUSEMOTION is, more than likely, the
124       event we're  looking  for.  A  little  more  research  tells  use  that
125       SDL_MOUSEMOTION  events  are  handled  within  the SDL_MouseMotionEvent
126       structure which is the motion member of SDL_Event. We can check for the
127       SDL_MOUSEMOTION event type within our switch statement like so:
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129           case SDL_MOUSEMOTION:
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131        All we need do now is read the information out of the motion member of
132       test_event.
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134             printf("We got a motion event.
135       ");
136             printf("Current mouse position is: (%d, %d)
137       ", test_event.motion.x, test_event.motion.y);
138             break;
139           default:
140             printf("Unhandled Event!
141       ");
142             break;
143         }
144       }
145       printf("Event queue empty.
146       ");
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148       It is also possible to push events onto the event queue and so  use  it
149       as  a two-way communication path. Both SDL_PushEvent and SDL_PeepEvents
150       allow you to place events onto the event queue. This is usually used to
151       place  a  SDL_USEREVENT on the event queue, however you could use it to
152       post fake input events if you wished. Creating your  own  events  is  a
153       simple  matter  of  choosing  the event type you want, setting the type
154       member and filling the appropriate member structure with information.
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156       SDL_Event user_event;
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158       user_event.type=SDL_USEREVENT;
159       user_event.user.code=2;
160       user_event.user.data1=NULL;
161       user_event.user.data2=NULL;
162       SDL_PushEvent(&user_event);
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NAME

STRUCTURE DEFINITION

STRUCTURE DATA

DESCRIPTION

USE

SEE ALSO