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copied!<p>I definitely would roll my own system in this case, and the performance loss versus using built-in animation code can be minimized using <code>CADisplayLink</code> rather than <code>NSTimer</code> (<code>CADisplayLink</code> is directly tied to the on-screen updates timer). </p> <p>The fact that you have 20 clouds simultaneously doesn't really change things too much, as I presume your intention is to animate those 20 clouds separately using the built in animations already.</p> <p>If you're unsure of how big of a performance hit it will have on things in the end, you could try simply adding a bunch of clouds (50 or so) using the built in animation and see how sluggish they move, then switching it out to built-in animation code and comparing.</p> <p>Edit: this discussion on Stack Overflow goes into detail on how to do what you're asking, in case you go that route: <a href="https://stackoverflow.com/questions/554997/cancel-a-uiview-animation">Cancel a UIView animation?</a></p> <p>Example:</p> <pre><code>// startAnimating called once to initiate animation loop. might be stopped e.g. // if game is paused or such - (void)startAnimating { // displayLink = the CADisplayLink for the current animation, if any. if (displayLink) { [displayLink invalidate]; [displayLink release]; } displayLink = [[CADisplayLink displayLinkWithTarget:self selector:@selector(animationTick:)] retain]; [displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode]; } // tick method is called at every interval; we want to update things based on // a delta time (duration), so that if things get bogged down and the updates // come less often, we don't go into slow motion - (void)tick:(CADisplayLink *)sender { CFTimeInterval duration = sender.duration; // here, we update the position for all the UIView objects. example: CGRect cloudFrame; for (UIView *cloud in clouds) { cloudFrame = cloud.frame; cloudFrame.origin.x += windForceX * duration; cloudFrame.origin.y += windForceY * duration; cloud.frame = cloudFrame; } // here we might update the windForceX and Y values or this might happen somewhere // else } </code></pre>

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