Ok, a little update on the skin shading, especially the calculation of the stretch correction map.

OPENGL & DERIVATION INSTRUCTIONS

I encountered a problem with the implementation of the stretch-map rendering. I use the ddx() function to get the derivative of the world position in UV space, i.e. how much the world position changes from one pixel to the next. This way you get a nice approximation of the texture coordinate distortion. For more information about the whole process have a look at my previous post here.

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Interactive demo of my skin shader:

 skin shading | unity demo

(requires the Unity Web Player plugin)

If you see only a black head, then probably your graphics card does not support ShaderModel 3 (only Nvidia GeForce-6, Ati Radeon-X1000 or newer).

For older graphics cards I captured a video of the demo:

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