CUDA Path Tracer

University of Pennsylvania, CIS 565: GPU Programming and Architecture, Project 3

• Liang Peng
• Tested on: Windows 10, i7-6700HQ @ 2.6GHz 2.6GHz 8GB, GTX 960M (Personal Laptop)

Feature

• Ray Scattering
  • Diffuse
  • Refraction
  • Specular Reflection
  • Glossy Reflection
• Depth of Field
• Stratified Antialiasing
• Performance Analysis

Overview

The image is rendered by a path tracer on GPU, with trace depth 8 and 5000 samples per pixel. Features include diffuse, glossy, specular reflection, refraction, depth of field, and stratified antialiasing. The image is produced by averaging the results of all large amount of iterations. In each iteration, the camera will shoot a ray through each pixel and intersect with the scene objects. Based on the material at the intersection point, each ray will change color and be reflected towards certain direction and continue tracing. As a ray reaches it trace depth, its color will be accumulated to compute the final color.

Ray Scattering

• Lambert Diffuse

Trace Depth 2, SPP 1000	Trace Depth 8, SPP 1000
observation Images rendered with deeper trace level appear darker, which is due to the calculation of ray color. The resulted color is calculated by multiplying the material color of all intersections along the path.

• Refraction

Refraction 1, SPP 1000	Refraction 2, SPP 5000
observation Since large amount of paths are traced, caustics produced by refraction are free.

• Specular Reflection

Trace Depth 2, SPP 1000	Trace Depth 8, SPP 1000

• Glossy Reflection

Less Glossy Floor, SPP 3000	Glossier Floor, SPP 3000
obervation For different types of material, glossiness can be adjusted by tuning the specular exponent. Larger exponent produces reflection closer to mirror.

Depth of Field

Depth of Field, Far Focal	Depth of Field, Near Focal
obervation There are 2 parameters we can play around with in terms of depth of field, lens radius and focal distance. Larger lens radius produces stronger DoF effect. Focal distance affects the distance the virtual camera is focusing on.

Antialiasing

Antialiasing OFF	Antialiasing ON
obersvation By jittering the camera ray within the ray's own pixel and performing large number of iterations, the final color of a pixel is computed by averaging all rays going through the pixel, producing antialiased image.

Performance Analysis

• Trace Depth

Depth	1	2	3
Time	38 ms	70 ms	93 ms
Image
Depth	4	5	6
Time	110 ms	120 ms	140 ms
Image
Depth	7	8	9
Tim3	148 ms	156 ms	160 ms
Image

Observation Apparently, as trace depth increases, image quality becomes better. Interestingly, time spent on 1 iteration increases with decreasing rate, that is probably due to the fact that as a ray traces deeper, it is more likely to hit nothing or terminated, thus need no more calculation.