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The argument in favour of a GPU-accellerated GUI which is not mentioned here is battery life. I haven't been testing this side of things, but just because a CPU can do a 60 FPS GUI doesn't mean it should. Deferring it to the GPU would certainly reduce power consumption while navigating a UI.

Both Charles Ying of Satine and wzdd seem sympathetic to this notion that the gpu is a power saving device. Surely it is when doing complex work. On the other hand, most smartphone usage consists of relatively simple screens and basic if any transitions. If it's only going to take 3ms of CPU work to run a 150ms animation, by all means, figure out how to keep the OS from interrupting the high priority graphics task and make the CPU do it. Particularly if the GPU would have to be on across the entire 150ms. If not, what is the cost of copying the graphical content between the GPU and the CPU? How much CPU does it take to initialize and set up the GPU for this extremely simple task you ask of it? Is the CPU going to be able to sleep while the GPU is running the animation, and if not what kind of context switching and control costs are going to be imposed on the CPU to manage the graphics state?

We've barely begun to see multi-core cell phone GPU's, but the point of the GPU is basically to run lots of work at a nice low clock rate where voltages can be dropped. If you dont have a lot of work to do, there's really no sense waking up the GPU and having it's extremely dumb poorly-branching cores chug away at figuring out, say, the SVG animations that a semi-competent ARM core could knock off right quick. You're just wasting power turning on the GPU.

Smoothness and polish, I suspect, are much more a questions of resource allocation than CPU capability, particularly when you've got a sub 640x480 surface and a 1GHz core.




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