Is iOS using some form of dirty region rendering by default while rendering applications?
For example, if I have a graph paper background graphic on a text input field, and the user scrolls through it, will the whole graphic be redrawn every time, or only the part that has changed (In the graph paper example: If a pixel was white before and will be white on the next rendering, will it be redrawn or left alone)?
Again, this question is mostly out of curiosity and not out of programming needs. I did not find anything in the developer manuals about this.
Not only is Richard J. Ross III’s comment evidence — Apple have reserved the right to do partial redraws even though the iPhone had full on-GPU composition from day one, so it isn’t a legacy thing — but the advice always handed out in OpenGL sessions is to try to avoid composition of OpenGL on OpenGL or any two rapidly changing views since it causes the compositor to do a lot of extra work that you can usually avoid (by moving all the content into one OpenGL view in that specific case).
I would therefore assume the compositor has some notion of updating only dirty parts of the layer hierarchy.