GI - Photon Mapping - Day 2 (More Ray-Tracer Features)

I had some time to work on the Ray Tracer a bit more, I got specular, reflections, refractions and exposure working. I also added a simple camera control which enters a 'preview mode' that renders at slow but still interactive rates, this way I can move the camera and when I stop I get the scene rendered in normal (non-preview mode).
One thing I noticed is how easy it is to debug artifacts, just find the coordinates of the problem pixel and follow the ray...
One thing I am currently working on is removing any magical tolerances, I have seen such tolerances used in tutorials for cases such as: you have a ray colliding with a primitive, and you generate a new ray with the collision point as source but a new direction, you do not want the new ray to be detected as colliding with the source primitive. It is possible to solve this by using a small tolerance to move the collision point to the outside of the surface, I do not like that, because those tolerances are usually scene dependent, caused by the lack of floating point precision AND on the metrics and nature of the scene, that is why I like to avoid such work-arounds whenever possible even at the cost of some performance.
I changed the collision routines for the spheres to handle the cases cleanly without using any tolerances.

Next I will fix the plane intersection routines (for now all I have is spheres and planes) to handle the case as nicely.
After that, I will probably take a small break from adding 'features' and play around with some multi-core support for the ray tracer. Even if I did not add spatial subdivision yet, one important goal of this project is playing around with multi-core, so the sooner that happens the better, even if the 'single-core' version is not optimized yet.

A screenie for the record.