What's the magic behind CAReplicatorLayer?

Question

What I find interesting with CAReplicatorLayer:

• It is able to display a CALayer multiple times with different transforms very efficiently (how?)
• It seems like it somehow reuses the "backing store" for the replicated layer and even apply some color tints to it (how?)

I would like to get hands on either the source code or get some knowledge of the magic behind CAReplicatorLayer. I would like to have a CALayer class similar to CAReplicatorLayer, but with more control. I would like to have control on the transform individually for each replicated instance.

So asked in a totally different manner: is it possible to get the "backing store" for a CALayer and display it however I want as many times I want?

(by "backing store" I mean the rendered texture for the CALayer/UIView. I don't know much about what's happening under the hoods of CoreAnimation/QuartzCore).

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Why I'm not looking at alternatives like e.g. rendering the CALayer to a UIImage:

• Performance
• Content is dynamic/changing pretty frequently under the transitions
• It would be hands down awesome to do it the other way!

Loris

Been wondering this myself. Hope someone smarter than us comes along haha. – Prolongation

Answer 1

The special-purpose CALayers like CAReplicatorLayer or CAGradientLayer are able (via private APIs) do execute their drawing directly on the GPU using fast filling or copying. In a sense they are different such that the backing store is not in normal RAM, but directly on the GPU.

Pacificas

Thanks for the response. That does not sound promising for what I was hoping to do, but indeed clarifies some aspects. :) – Loris

you can always use an EAGLLayer and draw on that with OpenGL with shaders. This would be the fasted way to do custom drawing. – Pacificas

I suppose I can't do that backed by UIViews? Or in my case: I'm doing something as bold as replicating a UIWebView. I would very much like something similar to CAReplicatorLayer, but with control over each individual instance' transform (instead of the incremental one CAReplicatorLayer offers). If OpenGL/EAGLLayer offers that I would be more than happy. – Loris