There is still a limit to how much the GPU can do. A recent interesting example of this is tablets built with Tegra 2 -- that GPU can touch every pixel of a 1024x800 screen about 2.5 times at 60fps. Now consider the Android 3.0 tablet home screen where you are switching to the all apps list: you need to draw the background (1x all pixels), then the layer of shortcuts and widgets (let’s be nice and say this is .5x all pixels), then the black background of all apps (1x all pixels), and the icons and labels of all apps (.5x all pixels). We’ve already blown our per-pixel budget, and we haven’t even composited the separate windows to the final display yet.
I find this bizarre. Are all of these drawing operations using alpha blending (using translucency)? If so: is that strictly necessary for the entire area of all of them?
If they aren't using blending, why on earth do they have so much overdraw? The GPU could reduce that to touching each pixel exactly once by using the Z buffer and drawing in front-to-back order.