iOS / Core-Animation: Performance tuning

Question

I have my app running on my iPad. but it is performing very badly -- I am getting below 15fps. can anyone help me to optimise?

It is basically a wheel (derived from U

Answer 1

I know this question is old, but still up to date. CoreAnimation (CA) is just a wrapper around OpenGL - or meanwhile maybe around Metal. Layers are in fact textures drawn on rectangles and the animations are expressed using 3D transformations. As all of this is handled by the GPU, it should be ultra fast... but it isn't. The whole CA sub-system seems pretty complex and translating between AppKit/UIKit and the 3D world is harder than it seems (if you ever tried to write such a wrapper yourself, you know how hard it can be). To the programmer, CA offers a super simple to use interface but this simplicity comes with a price. All my attempts to optimize very slow CA were futile so far; you can speed it up a bit but at some point you have to reconsider your approach: Either CA is fast enough to does the job for you or you need to stop using CA and either implement all animation yourself using classic view drawing (if the CPU can cope with that) or implement the animations yourself using a 3D API (then the GPU will do it), in which case you can decide how the 3D world interacts with the rest of your app; the price is much more code to write or much more complex API to use, but the results will speak for themselves in the end.

Still, I'd like to give some generic tips about speeding up CA:

• Every time you "draw" to a layer or load content into a layer (a new image), the data of the texture backing this layer needs to be updated. Every 3D programmer knows: Updating textures is very expensive. Avoid that at all costs.
• Don't use huge layers as if layers are too big to be handled directly by the GPU as a single texture, they are split into multiple textures and this alone makes performance worse.
• Don't use too many layers as the amount of memory GPUs can spend on textures is often limited. If you need more memory than that limit, textures are swapped out (removed from GPU memory to make room for other textures, later on added back when they need to drawn). See first tip above, this kind of swapping is very expensive.
• Don't redraw things that don't need redrawing, cache into images instead. E.g. drawing shadows and drawing gradients are both utlra expensive and usually rarely ever change. So instead of making CA draw them each time, draw them once to a layer or draw them to an image and load that image to a CALayer, then position the layer where you need it. Monitor when you need to update them (e.g. if the size of an object has changed), then re-draw them once and again cache the result. CA itself also tries to cache results, but you get better results if you control that caching yourself.
• Careful with transparency. Drawing an opaque layer is always faster than drawing one that isn't. So avoid using transparency where not needed as the system will not scan all your content for transparency (or the lack of it). If a NSView contains no area where its parent shines through, make a custom subclass and override isOpaque to return YES. Same holds true for UIViews and layers where neither the parent, nor their siblings will ever shine through, but here it is enough to just set the opaque property to YES.

If none of that really helps, you are pushing CA to its limits and you probably need to replace it with something else.