SGIS_Shadow & Cube Maps = No 'R' Coordinate

Since the SGIS_shadow specification (using the latest nvOpenGLspecs.pdf) says it uses compares the ‘R’ coord with the texel fetched from ‘S’ & ‘T’, is there anyway to use this with cubemaps? or 3d textures for that matter?

It would be great if the spec was appended with “it uses ‘Q’ coord when cube or 3d textures are enabled.”

The percentage-closer-filtering-comparision has a lot of value for cube/3d maps beyond shadows.

No, cubemaps are not supported in any meaningful way. I also suggest not using this with 3D textures. (These ambiguities are one reason why this is only an SGIX extension.)

  • Matt

Thanks Matt-

If there was enough support/demand, would it be possible to add such an extension for GF3-class HW that could apply compare & percentage-nearest filtering on cube/3d maps?

No; for example, shadow cubemaps require very different math than 2D shadow maps.

  • Matt

It’s an interesting request though. The texgen for the R coordinate would not work with this, but perhaps another texture would do the trick. A simple 3D texture which mapped light distance radially with the comparrison against projected depth texture from the light projected using a cube map style representation. The 3D texture needn’t be perfectly radial, it could support the planar depth for each cube face if the depth cube map didn’t contain radius but cube face z.

[This message has been edited by dorbie (edited 01-20-2002).]