Reading contents of android-layer

Question

I'm working on a project that involves reading the content of a layer that is to be composited by the surfaceflinger.

I specifically need to check whether the layer to be composited is all 1-bits 0r all 0-bits.

This is to apply some optimizations before composition by the SurfaceFlinger.

I tracked the creation of the buffers via adb-logcat(by adding my own log messages) but couldn't find a way to read the actual contents of the layer.

Could anyone tell me if this is even possible, and if it is, how?

Answer 1

In general, it's not. For example, if the layer is displaying DRM-protected video, it's impossible to read the data.

For unprotected layers, you can read the pixel values out with glReadPixels() -- there's some code in SurfaceFlinger's screenshot code that can be enabled to check for blank screenshots -- but this is going to be slow.

Bear in mind that not all layers are RGB. If the layer is YUV, an "all zero" layer would actually be a dull green.