This shader computes lighting and shadowing in volumetric data (ie. a 3d texture). The idea is to implement a ray marcher directly into the fragment program of the NV30. Each time a pixel textured by the volumetric data is rendered, a ray is cast towards the light. Densisty is integrated along the ray and then exact lightning is computed. This method allows to render colored shadows of semi-transparent objects. Thanks to CG and NV30 this can be entirely done in hardware. Moreover, if the 3d texture is applied to a geometric model the lightning computation is only done if the pixel is visible.

"Simulate" a surface under rainfall. This shader was developped with the NV30 emulation driver. Movies of this animated effect as well as full source code are available.