ASST3_README

Computer Graphics 15662 Assignment 3 Pathtracer
Yang Zhou
Apr 8, 2016
I would like use grace day to delay the submission.

Extra credit:
1. Halton sequence sampling: I implemented Halton sequence sampling in 2D grid
[0, 1) x [0, 1). Pass the additional '-m' param to use it for generating pixel
ray. See sampler.cpp for details. Because generating halton sequence need to
store internal variables, it is thread unsafe to share one sampler across
multiple threads. Therefore, I remove the gridsampler inpathtracer.cpp, but
create a sampler in each thread function. However, there seems to be no visually
obvious difference....at least to me.

Images:
Both images are rendered with 64 pixel samples, 64 light samples, and 5 bounces.
I disabled Russian Roulette for better image quality. See img folder for details.

Other issues:
1. Ray-aabb intersection optimization: I slightly changed the sturcture of BBox
in order to perform branchless ray-aabb interection. instead of min and max
variable, I used a length 2 array bounds[2]. The method was inspired from this
paper [1].

2. I also implemented cosine-weighted hemisphere sampling. See sampler.cpp for
details.

3. As I mentioned on Piazza, the radiance of the emissive material in Cornnel
Box is (10, 10, 10), which seems to be out of range. This leads to a noisy image
with a lot of pure white pixels (larger than (1,1,1)). I regard this as a bug,
and fix it by saturating the radiance to (1,1,1)

4. I experienced some errors when importing an environment map. For example,
when importing uffizi.exr, the spectrum components of some pixels are zero or
(slightly) negative. I clamped those pixels to a small value larger than 0 because
inversion method requires non-zero probability mass function.

5. It turns out that the "Viewer" is not released properly. This is because its
deconstructor tries to delete app, which is not assigned by new operator (in
main.cpp). It can be simply fixed by one-line change:

(Before:) Application app(config);
(After:) Application* app = new Application(config);


Reference:
[1] Williams, Amy, et al. "An efficient and robust ray-box intersection
algorithm." ACM SIGGRAPH 2005 Courses. ACM, 2005.