[pcwalton]

Native widgets on iOS are rendered with the system compositor, Core Animation. If you render everything yourself into a GL or Metal context then you have to blit everything to the context, and then Core Animation blits your buffer to the screen. (This may be bypassed in full screen mode; I don't know. But in any case if you are using native widgets at all then you have this extra blit.)

This is a significant power consumption concern.

[tpush]

Not knowing anything about this, are there any numbers on the power consumption of that extra blit?

[zamalek]

I can't imagine it actually blits, it probably swaps buffers like everything since 2000.

[pcwalton]

No, it blits. Buffer swap doesn't work because Core Animation owns the entire scanout buffer. iOS apps don't have access to it.