Bending rays

What's a ray tracer without some good old caustics? With smooth shading normals in place the next logical step was to get specular transmission in there and refract some rays. Compared to the microfacet stuff I've been digging into for specular models implementing a perfect mirror model was reassuringly straight forward. I added a reflective mirror brdf for good measure and wrapped it all into a glass material. Tinting is currently done at the interface only - so no fancy volumetric absorption along the ray until I have a proper volume pipeline, but it does the trick for now.


EDIT2: I was using this scene as a performance test, but figured I could throw a sphere in there to show off the caustics as my other render was broken. 
2048x2048, 16 bounces, 1 mill polys, 15k samples per pixel (naive forward path tracing does not converge caustics particularly fast..):

Here's our hero with an index of refraction of 1.5:

EDIT: This one actually has a pretty hilarious - and rather obvious now that I've found it - bug. There are no caustics from direct light sources here (ie, Eye -> Diffuse -> Transmit -> Transmit -> Light paths), only from indirect lighting (Eye -> Diffuse -> Transmit -> Transmit -> Diffuse/Glossy -> Light), so only bounce from the floor is contributing to the caustics, not the light source itself. I'll leave the render up regardless, and post a correct one once I've wrapped up what I'm currently working on.

-Espen