This is a modern path tracer that implements various BRDFs (Cosine, Phong, Microfacet), PDF sampling, area lights and light sampling, importance sampling, and russian roulette. This project was extended to incorporate basic homogenous volume rendering. Made as part of CSE 168 at UCSD, and therefore I cannot share source code. I can share some renders, though!
Stanford dragon rendered with BRDF importance sampling and russian roulette. GGX microfacet BRDF. 128 samples per pixel.
Scene to demonstrate GGX microfacet BRDF, with balls of various textures. BRDF importance sampling and Russian Roulette. 64 samples per pixel.
The aim of this extension project was to use physically-accurate techniques to produce attractive images of rendered bounded volumes, such as glass, gel, or fog. I modified my Optix pathtracer implementation to achieve this.
Initially (as noted in the milestone), there was a persistent bug with banding. It turned out that the bug was limited to spheres, and that it was very unclear where it was coming from, so I opted to continue with only triangles being rendered as volume boundaries. I proceeded to also add attenuated shadow rays, so that volumes would not always have full shadows. Below is a picture of exponential distance attenuation applied to a box, with partial shadows.
Next I added a surface BSDF. I used a variant of the glass bsdf, in which the decision on whether to reflect or transmit is based on a calculation of the Fresnel term (via Schlick's Approximation). If transmitting, the direction remains unchanged, while if reflecting, it follows the previously implemented phong brdf. Then, I added support for single scattering at a random point in between each pair of collisions inside a volume, with an isometric (1/4pi) phase function. See image below.
Next, I added support for emission, attenuated by absorption. I also went back and modified the phase function I used, from isometric to Henyey-Greenstein. In a similar vein, I changed the transmission code in the BSDF to use Snell's law of refraction, changing direction based on the indices of refraction of the two mediums. Now I was able to produce, for example, colored glass (g= -0.75, for backscatter):
With some experimentation in specular color, index of refraction, absorption and scattering coefficients, and emission, I was able to produce these images [ice cube, jade dragon, gel dragon, glass dragon]:
