Bidirectional Path Tracing Enhancements

Several months ago, I implemented a couple additional bidirectional path tracing features described in Veach's thesis. Specifically, I added support for ideal specular BSDFs and support for special direct illumination sampling strategies. Below are some renders illustrating these features. Click the images to view them at full size.

Specular BSDFs:

The metallic ball, the smooth parts of the checkered glass ball, and the small glass ball use ideal specular BSDFs.

Direct illumination: 

Render without a special direct illumination sampling strategy.

Render with a special direct illumination sampling strategy. Samples are distributed uniformly over the solid angle subtended by the lights.