Rectangular Light Source

The last few days I was in the debugging of penumbra shaders for rectangular light source. All my previous soft shadows implementations supported spherical light sources only and with rectagular light there was an incorrect shading. In the end I wrote a shader algorithm in C++ and debugged a few test cases. It turned out that the correct solution requires inverting 3x3 matrix directly in the pixel shader, which in the original implementation of the algorithm I haven't seen. Software implementation helped to understand all the subtleties of the algorithm (that's almost impossible with HLSL and GPU-oriented tools).

Due to low-poly geometry and rectangular shape of light source penumbra looks a bit angular. But the major problem is "single point silhouette approximation", I've written about it here (sorry, in russian). Because of this simplification the shadow looks like overshadowed, because not all potential silhouette edges contributed to penumbra. I don't like how the shadow looks, so I plan to implement more sophisticated silhouette edges determination.