Physically Based Path Tracer

This repository contains the implementation of a physically based monte carlo path tracer in C++. The project avoids the use of graphics API's and attempts to implement simple physically based rendering effects from scratch.

This is a project I essentially come to in my free time and is something I intend to update sporadically. If you have read the code, or tried to create a scene and have found any flaws or errors in the way things have been done — do feel free to leave an issue!

Note: The above 3D model for the Head of Michelangelo's David bust was taken from here. Other .obj models taken from The Stanford 3D Scanning repository

Denoiser

Noisy Render (Output)	Normal map	Albedo map	Denoised Image

Since the application runs on the CPU, samples per pixel needs to be limited to obtain reasonable render times (even with multi-threading).

The images shown above are denoised using Intel® Open Image Denoise. The pre-compiled zip file from their website (unzipped, includes a bin and a lib folder) needs to be moved into src/dependancies/, for the shell script denoise to work.

Features

• [x] Motion Blur
• [x] Antialiasing
• [x] Depth of Field
• [x] Bounding Volume Heirarchies
• [x] Multithreaded pixel processing
• [x] .obj meshes
• [x] Importance Sampling
• [x] HDR Environment maps
• [x] Optimized and Multithreaded mesh BVH tree building
• [x] Non-ideal materials and BSDF's (Disney BSDF)
• [ ] CUDA optimized

Usage

A sample binary has been uploaded with the repo (compiled on x86, as a 64 bit application), but its unlikely that it would generally work even on a system with the same configuration (try anyway, it just might).

CMakeLists.txt is given and the project can easily be compiled using the cmake build system.

mkdir build && cd build 
cmake .. 
make

After compiling the project, the compiled binary (path-tracer) can be found in the bin/ directory and is to be used with a single command line argument - the name of the scene in src/scenes/. (The folder src/scenes/ contains implementation of all the scenes in this readme file)

./bin/path-tracer GlowRoom

Running this should show a progress bar, after which 3 images will be stored in output/noisy_render, output/albedo_maps, and output/normal_maps. After these three images have been generated, the denoise shell script can be run to denoise the image

./bin/denoise GlowRoom

The resolution of the output render and the samples per pixel have been hard-coded in main.cpp

Dependencies

• OpenMP was used for multi-threading the ray shooting and BVH tree building.
• (stb_image and FreeImage) were used to handle images.
• GLM was used for mathematical data types (vectors, matrices, etc.) and operations.
• ImageMagick is required for conversions in the denoise shell script.

Resources

This project takes a lot from Ravi Ramamoorthi's course - An intro to graphics; and the repository and code largely takes its structure and features from Peter Shirley's book series.

The Disney BSDF, though poorly incorporated and incomplete, takes a lot from this repository and the corresponding blog articles. Inspiration was also taken, but to a lesser extent from tinsel from mmacklin and GLSLPathTracer from knightcrawler25.

And just like everyone ever who has written a path tracer, constant references were made to Physically Based Rendering by Matt Pharr, Wenzel Jakob, and Greg Humphreys and its repository.

Note

This was more or less a pet project to be able to learn the fundamental basics of path tracing, and with every feature I added, I ended up wanting to add more.

I have licensed this project under the Zlib license, and do what you may with the code but I would highly recommend not to re-use the bsdf namespace and the core::Disney class, since some of the lobe calculations are off.