Retreiving texels and NV_texture_shader

[Ozzy]

don't know if it possible but i would like to implement a simple scan through a texture3D. As far i can see you can specify s,q,r coords with NV_texture_shader2 but is there a way to retreive texels and to compare their respective RGBA values? at least with 0,0,0,0 ;) ?

[pseudo code:]
bind tex3D
setup step..

while (texel[texCoord(step.x,step.y,step.z)] == 0,0,0,0){
step += ray
}

This kind of scan should be easier to implement with a fragment program but i would like to *try* to implement it for GF3 series that support hw texture3D.

thx for any info.

[zeckensack]

That sounds like dynamic flow control. I doubt it can be done at all (there's a hard indirection limit on ARB_fragment_program), let alone on NV20.