Does shouldRasterize on a CALayer cause rasterization before or after the layer's transform?

Question

I'm attempting to optimize my app. It's quite visually rich, so has quite a lot of layered UIViews with large images and blending etc.

I've been experimenting with the shouldRasterize property on CALayers. In one case in particular, I have a UIView that consists of lots of sub views including a table. As part of a transition where the entire screen scrolls, this UIView also scales and rotates (using transforms).

The content of the UIView remains static, so I thought it would make sense to set view.layer.shouldRasterize = YES. However, I didn't see an increase in performance. Could it be that it's re-rasterizing every frame at the new scale and rotation? I was hoping that it would rasterize at the beginning when it has an identity transform matrix, and then cache that as it scales and rotates during the transition?

If not, is there a way I could force it to happen? Short of adding a redundant extra super-view/layer that does nothing but scale and rotate its rasterized contents...

Answer 1

You can answer your own question by profiling your application using the CoreAnimation instrument. Note that this one is only available in a device.

You can enable "Color hits in Green and Misses Red". If your layer remains red then it means that it is indeed rasterizing it every frame.