Question

From the documentation it appears that core animation layer is above OpenGL and Quartz2D. i.e.
executing a core animation command should produce a sequence of Quartz2D and OpenGL commands Am I right?

In interface builder, under the View Effects tab, we can set the core animation layer. What happens internally there?When we tick Context View option, contents on screen (buttons, scrolls etc) are not drawn using main context or currentContext(view), but new Bitmap Context is created for them. What is happening under the hood there?

Can somebody please explain me relationship between CoreAnimation Layer and Quartz2d/OpenGL?

Answer 1

Core Animation layers are essentially high-level abstractions of OpenGL surfaces. They are stored and manipulated by the GPU and so manipulation of the layers is extremely fast. CALayer objects by themselves are very lightweight and have no event handling.

Layer-backed NSView objects (which is what you get if you enable the checkboxes in Interface Builder) are views that draw their content into a Core Animation layer, again stored in the GPU’s memory and with the same performance advantages as plain CALayer objects, but with all the functionality of a normal NSView.

What happens is that the view’s content is rendered (via Quartz) to its backing layer (essentially an OpenGL texture). The view then only needs to draw again if the content of the layer changes.

Changes in position, scale, rotation etc of the view’s layer do not require the view’s content be redrawn. This means that most of the time the CPU does not have to get involved in constantly redrawing the view.