[Bf-python] Fastest way for RenderEngine to return combined rgba + z

[Asbjørn]

On 19.08.2013 16:59, Asbjørn wrote:
> On a single 1920x1080 image with alpha and depth (zbuffer), it takes
> about 1.2 seconds total to update and transfer the image to the render
> result. About 400 ms is spent on our side tonemapping etc and converting
> to bottom-up format (internally we store top-down). The remainder, about
> 800 ms, is spent getting the result into Blender using the foreach_set.
> This was measured in different ways on my i7 2700k.

Here are some more detailed timings:

begin_result:  2 ms
blenderCombinedDepthBuffers:  366 ms
layers.foreach_set:  21 ms (color)
passes.foreach_set:  2 ms  (zbuffer)
end_result:  780 ms

The "blenderCombinedDepthBuffers" is our function, which performs 
tonemapping and merges the color and alpha data into a single rgba float 
buffer, which it returns along with the zbuffer.

Does the end_result involve uploading the data to OpenGL or similar? I'm 
a bit surprised it takes so long.

Cheers
- Asbjørn