Nori

About

Nori is a minimalistic ray tracer written in C++. It runs on Windows, Linux, and Mac OS and Nori 2 was built for the course Advanced Computer Graphics taught at EPFL. We are using a lightly modified version of Nori 2 as the framework for our assignments in CS 5630. (Historical note, Nori made its debut in CS 6630 fourteen years ago.)

While Nori provides a lot to simplify your development work, the starter code achieves very little: it loads a scene and saves a rendered image as an OpenEXR image—but the actual rendering code is missing, so the output image is all black. Your task will be to extend this system to a full-fledged physically-based renderer as part of the programming assignments and your final project.

Note: Nori is used to teach rendering at several universities and many people have put a lot of work into it. Its value as a teaching tool can easily be undermined by solutions that are available on the web. Therefore do not ever post the code for Nori or the solutions you build using it anywhere in public. Doing so is not only destructive to learning but is also a violation of the license terms under which the code is distributed.

Core features

The Nori base code provides many features that would be tedious to implement from scratch. The following are included:

A simple GUI to watch images as they render
An XML-based scene file loader
Basic point/vector/normal/ray/bounding box classes
A pseudorandom number generator (PCG32)
Support for saving output as OpenEXR files
A loader for Wavefront OBJ files
Ray-triangle intersection
Code for multi-threaded rendering
Image reconstruction filters
Statistical \(\chi^2\)- and \(t\)-tests to verify sampling code
A graphical visualization tool that can be used to inspect and validate sampling code
An efficient ray intersection engine with a parallel bounding volume hierarchy builder (distributed separately from the base code)

References

You may find the following general references useful:

"Physically Based Rendering, Fourth Edition: From Theory To Implementation" by Matt Pharr, Wenzel Jakob, Greg Humphreys. Morgan Kaufmann.
"Robust Monte Carlo Methods for Light Transport Simulation", PhD Thesis by Eric Veach, Stanford University, December 1997.

Feel free to consult additional references when completing projects, but remember cite them in your writeup.

Guidelines for homework submissions

The goal of these exercises is to help you create the foundation of a good renderer for subsequent assignments and the rendering competition. It is your job to convince us that you have implemented the assignments correctly, through the information provided in your reports and the quality/readability of your code. So incomprehensible code or inconclusive comparisons/validations in your report won't get you full credit even if your program works. Make sure to start working on the assignments early enough to leave plenty of time puzzle over things and to ask for help. Building your own advanced renderer is a lot of fun! But it doesn't always go smoothly.

What to submit?

Source code submission is handled via CMSX. For each assignment you will write a small report that should adhere to the following conventions:

You'll hand in a GitHub URL that points to a specific commit in your COECIS GitHub repository, which has your source code, your report html file, and also supporting results from your program.
Structure your report using numbers and titles following those of the assignment.
Nori automatically generates both a .exr as well as a sRGB tonemapped .png image of your rendering that can be directly used for the comparisons in your report. You are required to commit both versions in your results/ folder.
Include descriptions of encountered problems, a list of external libraries that you used (if applicable) and the time you spent on each task.

The task descriptions may contain more specific instructions on what to include.

Comments

We invite any comments or criticism to improve the projects in future classes. Please use the first section of your report to provide feedback—naturally, this part won't affect your grade. Examples of useful information include:

How much time did you spend on the assignment? How was it divided between designing, coding, and testing?
What advice should we have given you before you started?
What was hard or surprising about the assignment?
What did you like or dislike? What else would you change?

Late submissions

We allow for the total of 4 late days. You can use these late days for any assignments except for the final project submission. Each late day allows you to submit an assignment up to 24 hours after the deadline without penalty. Once you have used all 4 late days, grade for any further late submission will be reduced by 50%. Assignments in this class are very dependent on each other, so this policy is here to encourage you to submit on time.

Nori an educational ray tracer