Spherical harmonics self-shadowing

Valve's self-shadowing radiosity normal maps concept can be used with spherical harmonics in approximately the same way: Integrate a sphere based on how much light will affect a sample if incoming from numerous sample direction, accounting for collision with other samples due to elevation.

You can store this as three DXT1 textures, though you can improve quality by packing channels with similar spatial coherence. Coefficients 0, 2, and 6 in particular tend to pack well, since they're all dominated primarily by directions aimed perpendicular to the texture.

I use the following packing:
Texture 1: Coefs 0, 2, 6
Texture 2: Coefs 1, 4, 5
Texture 3: Coefs 3, 7, 8

You can reference an early post on this blog for code on how to rotate a SH vector by a matrix, in turn allowing you to get it into texture space. Once you've done that, simply multiply each SH coefficient from the self-shadowing map by the SH coefficients created from your light source (also covered on the previous post) and add together.

Introducing RDX

Has it really been a year since the last update?

Well, things have been chugging along with less discovery and more actual work. However, development on TDP is largely on hold due to the likely impending release of the Doom 3 source code, which has numerous architectural improvements like rigid-body physics and much better customization of entity networking.


In the meantime, however, a component of TDP has been spun off into its own project: The RDX extension language. Initially planned as a resource manager, it has evolved into a full-fledged programmability API. The main goal was to have a runtime with very straightforward integration, to the point that you can easily use it for managing your C++ resources, but also to be much higher performance than dynamically-typed interpreted languages, especially when dealing with complex data types such as float vectors.

Features are still being implemented, but the compiler seems to be stable and load-time conversion to native x86 code is functional. Expect a real release in a month or two.

The project now has a home on Google Code.