Comment by pcwalton

For the most part that's true, but simple 2D compositing is a bit of a different beast, because it can sometimes be done at scanout time, saving a blit. Last I checked, (non-Android) Linux rarely makes use of this except for the mouse cursor. But in general you can save a good bit of energy and memory bandwidth on HiDPI displays if you try to use 2D hardware layers where you can. You can virtually never use them for the UI itself, because they're far too limited, but the windowing system can often use them to composite windows together. It'd be nice if Wayland compositors made more use of this, e.g. to avoid having to blit the foreground window every frame.