Rendering loop in a game - ios

Question

I need to organize rendering loop in my app by a specific way (there is a reasons).
Let's say I have
Sprite *sprite = [[Sprite alloc] initWithContentsOfFile:#"sprite.png"]; // some sprite
while (true) {
[Graphics update];
sprite.x = (sprite.x + 1) % 1024 // moving sprite by one pixel each frame
[Input update];
[self update];
}
There Graphics.update should render one frame and delay execution (not rendering) until next frame
#interface Graphics () {
static BOOL _frozen;
static int _count;
static int _frameCount;
static float _frameRate;
static double _lastFrameTimestamp;
}
#end
#implementation Graphics
+ (void)initialize {
_frozen = NO
_count = 0
_frameCount = 0
_frameRate = 30.0
_lastFrameTimestamp = CACurrentMediaTime()
}
+ (void)freeze {
_frozen = YES;
}
+ (void)update {
if _frozen
return
end
Video.nextFrame // some OpenGL ES magic to render next frame
_count++
now = CACurrentMediaTime()
waitTill = _lastFrameTimestamp + _count * (1.0 / _frameRate)
if now <= waitTill
sleep(waitTill - now)
else
_count = 0
_lastFrameTimestamp = CACurrentMediaTime()
end
_frameCount++
}
#end
Somehow it works and sprite is moving. But when I go to home applicationWillResignActive isn't called and when I go back to app there is black screen and after some time app crashes.
Here is the thing I try to port: https://bitbucket.org/lukas/openrgss/src/7d9228cc281207fe00a99f63b507198ea2596ead/src/graphics.c (Graphics_update function)

Answer 1

You can try using Core Animation DisplayLink instead of a while loop. That's how it's usually done in the graphics frameworks. The currentRunLoop calls your update method every 1/60 seconds.
You should remove the sleep call in your update if using NSRunLoop.
CADisplayLink *displayLink;
// Set your update method
displayLink = [CADisplayLink displayLinkWithTarget:[Graphics class]
selector:#selector(update)];
// Set fps to device refresh rate (60)
[displayLink setFrameInterval:1.0f];
// Add your display link to current run loop
[displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
// Stop updating
[displayLink invalidate];
The last line stops the execution, so do not call that until you're done with your loop.

Answer 2

If you are using Sparrow, this is how you should be handling it:
SPSprite *sprite = [[SPSprite alloc] initWithContentsOfFile:#"sprite.png"]; // some sprite
[self addEventListener:#selector(enterFrame:) atObject:self forType:SP_EVENT_TYPE_ENTER_FRAME];
-(void)enterFrame:(SPEnterFrameEvent*)e {
[Graphics update];
sprite.x += 1; // moving sprite by one pixel each frame
[Input update];
[self update];
}
Sparrow manages the game loop for you using an SP_ENTER_FRAME_EVENT. It will be called every time it's time to render again. Roughly 30 times per second (though it can be configured).