Penumbra shadow map screen shot

I have implemented some part of the penumbra soft shadow map idea. I need more time to implement the actual shadow part, but today I got the penumbra map.

I found that we can use shader programs even with wire frame fill mode; I am not sure whether or not it can be faster than solid fill mode. Therefore I could implement shaders that generate a derivative image directly with rendering wire-frame model.

I like to show some of screen shots.

The first image is the scene from light perspective:

Then, the depth map is generated. The depth values are stored at Red and Green channels.

Finally, the derivative image is generated by rendering wire-frame fill mode:

Note that the leg parts of the elephant looks like blurred. It hasn't been blurred but because their derivative values are small. Thus I can expect that contact points between the disk and the elephant will have sharp shadow.

It fetches five times at quarter resolution and I didn't see any false-positive edges. Since the derivative values are 8bit data, they can be retrieved by linear filter.