RRT - Ray's Ray Tracer

RRT is a stochastic, multithreaded ray tracer written in C++ that relies on casting a very high number of samples per pixel into the scene and then scatters diffuse rays in every direction.

The method is far from efficient and producing a noise-free image may take thousands of samples per pixel (and hours of CPU time) but it produces effects "for free" that many other ray tracers can only approximate, including:

• diffuse inter-reflection (colour bleeding)
• area lighting and soft shadow
• glossy surfaces
• depth-of-field
• caustics

The current implementation supports only a limited number of 3D primitives:

• spheres (of course!)
• cubes
• infinite planes
• compound (parent node for collections of the above)

Arbitrary homogenous transformations are supported to move and deform primitives, but as yet these transformations cannot be nested. That is to say, a compound node cannot yet have a transformation that applies to all child nodes within it.

There is no scene description language - the user has to write a C++ program that makes call to the RRT APIs that create nodes, attach shaders to nodes, etc. See the example programs in scenes/ for more details.

The most powerful shader is Shader::stochastic that can take a surface object that is similar to those used in other ray tracers and will automatically cast a single diffuse ray, a specular reflected ray and a transmitted ray, depending on the surface's properties.

For a surface that has purely diffuse lighting properties the Shader::diffuse shader can be used instead and is slightly more efficient than Shader::stochastic because it doesn't have to consider the surface properties to decide whether to cast any non-diffuse rays.

There are no "lights" in RRT. Any object can have a Shader::constant shader attached to it that makes that object a fixed colour and indirectly causes it to "illuminate" any object that casts a ray in its direction.

Compiling

RRT requires a C++11 compatible compiler, Boost, GD, libpng, libjpeg and libz. The supplied Makefile is for Mac OS X with macports.

Running

Two samples scenes are included so far, "snooker" and "cornell".

The demo programs will either start a new render, or if passed a .rrt file as parameter will use that as the starting render buffer state. Every eight samples the current render buffer is rewritten to the .rrt file, as well as a 48-bpp PPM file. The netpbm package can be used to convert PPM files into PNG or JPEG, or many other formats.

TODO

• More primitives (especially meshes!)
• Bounding volume / Spatial acceleration techniques
• Compound transformations
• Time-based transformations (motion blur!)
• Ensure partial frames can't end up in the .rrt files

Sample Image

2048 samples per pixel, scaled 0.5, brightened slightly (pnmnorm -wv 170) and converted to JPEG with quality 95. This image demonstrates depth-of-field and image-based environment mapping, with all diffuse lighting generated from the environment map.