Shaders Galore! Texture-Space Diffusion, God Rays, and Light Extrusion Mapping!

Being several months overdue for a blog, I decided it was time to write one.

A great deal has happened over the past few months. I've done a lot of work with TGEA and have been working on an assortment of post-processing effects.

I am honored to say I am now an associate of Garage Games and hope to continue doing work to improve Torque technology.

For starters, I have written several iterations of deferred renderers. For those unfamiliar with a deferred renderer, the general idea is to save out
position and normal information from the entire scene into a texture. This allows you to control your lighting process almost entirely on the GPU.

I've written my own algorithm for Screen-Space Ambient Occlusion. In ambient occlusion, light comes in from every direction. My algorithms use the
8 surrounding cardinal directions to test for occlusion and shade based on that. It is run completely as a post-process using scene depth information and
requires only 8 samples, unlike many SSAO algorithms. The picture below is a crude example, using 32-bit precision. Good SSAO (and really, most post-processing effects) should use 128-bit textures. This does, however, have many performance drawbacks making a subtle effect such as SSAO somewhat pointless.


I've also been working on texture-based diffusion. While the terminology may confused some, it is really quite simple. You perform your diffusion and lighting in one pass, saving the result into a texture. You then perform many gaussian blur filters and adjust color operations to suit your needs. Then, the result is reapplied to the mesh and specular is calculated. The results produce soft, realistic skin. So far, the major problem with incorperating this into TGEA has been storing every diffusal texture, seeing as every mesh requires a new one.






SSAO and texture-based diffusion are great, but the real focus of this blog is to expose a new rendering technique I'm coining as "light extrusion mapping". Light is "extruded" from pixels on a texture map and the result is rendered as a post-process. This means NO geometry is being rendered for each ray. Many games are adopting similar effects, including Crysis and STALKER.
Plenty of neat effects can be done, some of which include god rays, foliage sun-scattering, and truely emissive images. Below are some of the results that can be accomplished with such light extrusion maps.






The really neat thing about this is that a light extrusion map is just a simple alpha channel, but it can easily be scaled to allow ranges of color from every channel.