We are using CALayerDelegate to get callbacks after we do setNeedsDisplay.

But according to https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/CoreAnimation_guide/SettingUpLayerObjects/SettingUpLayerObjects.html

Whenever we are subclassing CALayer with specialized layers like CAMetalLayer we should use override subclassed layer draw methods to perform our custom draw.