README file for Ray

In this assignment I implemented the following features:

    - Adpative super sampling
    - Shadows
    - Texture mapping
    - Refraction
    - Reflection
    - Multithreading
    - Use KD Tree

    - Point lights
    - Directional lights


I reused the classes from intersect, e.g. Intersect, Ray.

To build the reflection mechanism, I separate the function rayTraceImpl, which now accpets an additional parameter `recursionLevel`. Within the function I check whether the recursion level exceeds the maximum recursion level. If so, I stop the recursion, and if not the recursion continues. The color computed from sub-recursion will be added to the color of the current level, and multiplied by the reflection coefficients of the material of the current intersection.

The calcLight() function is adjusted such that the "eye" point is binded to the start position of the ray. In addition, to account for texture map, I add a method for each implicit shape called "getUV". Within getDiffuse(), I mixed the original diffuse color with the texture color to the the final color.

Some bugs of split() (the function that constructs KD-tree) are fixed where the surface calculation is incorrect when there are completly overlapped objects.

I also fixed bugs in ImplicitCylinder::intersect() and ImplicitCube::surfaceArea().

Changeble constants are put in RayScene.h (e.g. MAX_RECURSION, MAX_NUM_THREADS). You may modify them to have different results.

To implement refraction, I used the formula 16.33 in the textbook.

To implement adaptive super sampling, I followed the lecture slide.

Known bugs:
    The color of the spheres in refract.xml is slightly darker than the demo. I wasn't able to figure out why.