以前做Camera時為了解決VideoCamera取景時，在高分辨率下數(shù)碼變焦花屏的問題，找到的關(guān)于Copybit的資料，目前還沒找到出處。對Copybit沒有過多的研究，先貼到這兒，以后有時間好好研究一下。
Android HAL consists of several hardware accelerated modules, and copybit is one of them implemented in G1 phone.
WhileOpenGL ES cannot be used or it's in software implementation, copybit isused. Actually in cupcake branch, SurfaceFlinger always uses copybitinstead of GL if copybit is available -- but that's an oversight.
[[ Functions ]]
copybitis just an abstraction for a basic 2D blitter with support forrotation, scaling and color/pixelformat conversions. These features canbe supported in full or partially.
If the copybit module is present, then SurfaceFlinger will try to use it instead of using OpenGL ES.
Onthe G1 copybit is used for all window compositions and video playback(CC and scaling), on this h/w copybit is very fast and provide very goodup and down scaling.
[[ Donut Changes ]]
HOWEVER, on therelease after Donut, the copybit module won't be used by SurfaceFlingerdirectly, instead it will be used as a back-end for our software OpenGLES 1.x and SurfaceFlinger will only use the OpenGL ES API. Eventually,the copybit module will be phased out, instead, we will ask the ISV/OEMsto implement these features on their OpenGL ES drivers, if they thinkit is necessary.
[[ Usability ]]
If your h/w doesn't haveaccelerated GL, but has some sort of decent 2D blitter, you can write acopybit HAL module for it, and it will be used automatically bySurfaceFlinger -- at least under cupcake and donut.
[[ Limitations ]]
Thereare no mechanism to accelerate applications at the moment. Skia is apurely software renderer. It can greatly benefit from newer CPUs though,which have SIMD instructions, often, it'll be able to operate at busspeed in that case. We're working on optimization in that area.
If a device has a GPU, it makes no sense to implement copybit, because
(1) it won't be used by apps and
(2) SurfaceFlinger already uses the GPU for its work.
Now,if the device has an additional 2D part (like the G1), it is useful toimplement copybit, this way application won't have to share the GPU withSurfaceFlinger
