while( !done ) {
SDL_Event event;
while ( SDL_PollEvent(&event) ) { //WHY THIS LOOP?
if ( event.type == SDL_QUIT )
done = true;
if ( event.type == SDL_KEYDOWN )
if ( event.key.keysym.sym == SDLK_ESCAPE ) done = true;
}
keys = SDL_GetKeyState(NULL);
if ( keys[SDLK_UP] ) ypos -= 1;
if ( keys[SDLK_DOWN] ) ypos += 1;
if ( keys[SDLK_LEFT] ) xpos -= 1;
if ( keys[SDLK_RIGHT] ) xpos += 1;
DrawScene();
}
SDL_PollEvent in a loop? why???
Author
The quwestion is, why do i need the inner while loop. That's the code:
Well... suppose for example that the player was mashing 2 keys down per frame and you did not have the inner while loop. Every frame, 2 events would be appended to the queue, but only 1 would be taken off. If this happened, your game would get farther and farther behind on it's input processing. The while loop is there to process every event that has occured since the last frame, not just the first event that happens to be in the queue. I hope this helps to answer your question...
[edited by - evilsteve on May 26, 2004 3:16:31 PM]
I have a relating question.
How do you use SDL_PumpEvent() within your gameloop?
It doesn''t return anything nor does it accepts any arguements but yet its explicitly called by SDL_PollEvent(SDL_Event);
How do you use SDL_PumpEvent() within your gameloop?
It doesn''t return anything nor does it accepts any arguements but yet its explicitly called by SDL_PollEvent(SDL_Event);
Author
EvilSteve, ok it makes more sence now. Not for the particular example, but in another situation placing it in a loop would help. However the question about the endless loop is still there. Why the loop is not endless according to what i have said in the first post??
thanks
thanks
Vumaq,
I think that in most cases, you do not need to use SDL_PumpEvent, as it is used by SDL internally. It looks like SDL_PumpEvent does the work of querying the input devices, building the SDL_event structures, and placing them on the queue that is accessed by SDL_PollEvent. From the documentation, it sounds like the only time you would need to use SDL_PumpEvent yourself is if you were processing events using an "event filter" (see SDL_SetEventFilter) rather than SDL_PollEvent.
Because you don''t have an input device that can generate events fast enough to lock it up.
Travis is correct, but this is difficult to explain...
I believe the mouse itself is limited in how many events it can send to the computer in a certain amount of time. To see this, open up MSPaint, select the pencil tool, and draw a sharp curve as quickly as you can. You will notice that the curve is not smooth and is instead made up of several line segments. The mouse only had enough time to send as many movement events to the computer as there are line segments in that curve. If you had drawn the curve more slowly, there would be time for more mouse movement events to be sent to the computer, and therefore more line segments in the curve. So the inner loop will never loop indefinitly because the mouse itself is limited in how many events it can send per frame.
[edited by - evilsteve on May 26, 2004 3:50:40 PM]
SDL may have more than one event to return. For example, if I press "up arrow" and "left mouse button" at the same time, that is two events. In order to get all the information about every event that occured you must call SDL_PollEvents(...) until it returns 0, meaning that it has gotten every event.
Author
ok thanks for all the help 
One more question:
if i press 2 keys, and click my mouse too. In the event queue i''ll have trhee events waiting right?, or just the last one? I think i''ll have all the events. Am i right or wrong? If i am right, then i don''t need the inner loop cause the queue contains all the events...
so?
One more question:
if i press 2 keys, and click my mouse too. In the event queue i''ll have trhee events waiting right?, or just the last one? I think i''ll have all the events. Am i right or wrong? If i am right, then i don''t need the inner loop cause the queue contains all the events...
so?
This topic is closed to new replies.
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