How make a game loop on the iPhone without using NSTimer

Question

In order to cleanly port my game to the iPhone, I'm trying to make a game loop that doesn't use NSTimer.

I noticed in some sample code that, if using NSTimer, you'd set it up at the beginning with something like

    self.animationTimer = [NSTimer scheduledTimerWithTimeInterval:animationInterval target:self selector:@selector(drawView) userInfo:nil repeats:YES];

where drawView would look something like:

- (void)drawView 
{
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
    mFooModel->render();
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];
}

When using this technique mFooModel renders fine, but I instead want to make my own game loop that calls drawView instead of having NSTimer call drawView 60 times a second. I would like something like:

while(gGameState != kShutDown)
{
    [self drawView]
}

Unfortunately when I do this, all I get is a black screen. Why does this happen? Is there anyway I can implement what I'm describing here?

The reason I want to avoid NSTimer is because I want to do physics and AI updates in the game loop. I use my own clock/timer to keep track of the amount of time that has elapsed so that I can do this accurately. Rendering happens as fast as possible. I try to use some of the techniques as described in this article

This is somewhat of an impulsive question (the one you do after you've been coding all day, get stuck, and hope the answer is there by morning)

Cheers guys.

Answer 1

Another option with iPhoneOS 3.1 is to use the new CADisplayLink api. This will call the selector you specify when the screen contents needs to be updated.

displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(renderAndUpdate)];
[displayLink setFrameInterval:2];
[displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

The new OpenGL project template in XCode also use the CADisplayLink if you need some more example code.