Curvature

Curvature is an experimental hybrid raytracing / raymarching 3D engine written from scratch with one goal in mind: allowing light to be curved efficiently.

GIF above: orbiting around a 7x7 grid of spheres with a light-bending field at the center, which twists light in a fashion similar to the way magnetic fields bend the trajectory of electrons, and two light-repelling fields. The original 180 frame, 1920x1080, 2x anti-aliased render took about 8 hours to complete on a 8-core i9 2019 15" MacBook Pro running an earlier version of the software.

I have been working this as a fun side project since early 2019, mostly as a proof of concept for this improved algorithm I came up with.

This program implements standard techniques for raytracing acceleration such as BVH acceleration and multithreading support, but goes further with new, purpose-designed optimizations to accelerate curved lightpath rendering. At their core, these new techniques are inspired by ray-marching, and make use of distance functions to define safe, spherical zones where some calculations can be skipped in the iterative ray-curving process. In practice, these improve render time by 1.5x-4x, depending on the complexity of the scene. The engine represents the curvature of space as a set of bounded fields (which are free to intersect with each other or any normal object in the scene), which, given any point in space and a ray direction, return an incremental change in ray propagation. This way, a wide variety of light-bending fields can be defined. The engine is also intended to eventually support portals, and feature a more efficient path integration algorithm, improving the current, naive Euler method to the Runge-Kutta method.

Requirements

• standard library is used for data structures and threading (C++11 version used for development)
• CImg is required for writing images to files (version 292 used for development, but only extremely basic functions are used; older versions will likely work)
• GLM is required for all vector math (version 0.9.9.8 used for development, but again, standard features used only; older versions will likely work)

Compatibility Note

Curvature was developed on macOS, so there might be issues on Windows or Linux (especially the scene / mesh parsing code). Please let me know if you encounter / fix issues related to this.

Getting Started

At the moment, getting scenes onto Curvature is a bit messy. The RenderData class contains all the information needed by the RenderScheduler class to produce an image. You can either use one of its test constructors with a hardcoded test scene, or load a scene from a simple text file. The documentation for this file format doesn't exist yet, and it unfortunately doesn't support specifying fields at the moment. It is just simpler to hard-code a test scene by rewriting the test scene constructors, until this issue gets properly fixed. Hopefully more documentation will be produced looking forwards.

Acknowledgements

This project was possible thanks to educational ressources provided by many kind and brilliant people:

• Dr. Charalambos Charis Poullis, from Concordia, who formally introduced me to the world of Computer Graphics in his course. This project came together as an extension of my final project for this class, which was a simple raytracing engine. Some of the code given out as examples in this course served as a basis for writing MeshDataand RenderData's parsers.
• Inigo Quilez, who put together a treasure mine of information about distance functions, free for anyone to access.
• The people from Scratchapixel, who put together an amazing collection of easy to read articles about a vast array of ray-tracing and Computer Graphics techniques.
• Roman Wiche, who wrote a great, simple article about the surface-area heuristic BVH construction algorithm.