PathTracer2

Continue from PathTracer1, add more complicated materials, environment lights, and depth of field to ray tracer.

Part 1: Ray Generation and Intersection

Reflection and refraction

With sample rate of 256， 4 samples per light and max depth of 4.

Part 2: Microfacet Material

With sample rate of 256， 4 samples per light and max depth of 7.

Part 3: Environment Light

Importance sampling is introduced to increase the density of sample points in the regions that we are interested in.

Part 4: Depth of Field

Change aperture and focal distance to control the depth of field.