So what's up with the Cook Torrance shader?

Captain Obvious

New member
So... nobody is actually interested enough in having working specular shaders that they've even bothered to try the node I linked to?

Huh.
Not interested enough to bother circumventing the fact that I got blocked from the website by some content filter bullmanure.
 

Tobian

New member
I haven't tested it, but tbh, I don't really bother much with spec as a rule these days. It has it's uses, but I got a bit sick of fighting it, so I haven't bothered for a while! :)
 

gerardstrada

New member
So... nobody is actually interested enough in having working specular shaders that they've even bothered to try the node I linked to?

Huh.
Don't know if you have even bothered to try the node you linked to, but at least here, the Cook-Torrance and Phong models don't provide correct results in their backlighting distribution. The effect is interesting (and might be used for some rim lighting effects) but the thing is that their highlight distribution and intensities in backlighting is not consistent with the direction of the incoming light according to the direction of the viewer.

We suppose that the farther we measure from the center of the highlight, the lesser will be the intensity of the highlight; but the Cook-Torrance node and Phong node (as well as their shader versions) don't behave as expected. There, the back highlight intensities are higher than the center of the highlight, besides, the light is reflected in angles where the surface normal is not oriented between the direction of incoming light and the direction of the viewer (specular highlight spreads in a 180° range). Both cases don't represent the specular reflection of real materials. This odd behavior can not be excused by a fresnel effect and it can't be solved with their highlight/IOR parameters (the highlight parameter is not present in the shader and none of these parameters are present in the Phong model where the situation is more acute).

Options are always welcome, but for more predictable results and more extensive usages, I prefer the LightGroup node from Denis Pontonnier :)



Gerardo
 

Tobian

New member
Actually yes, well partly. the part of the bug which causes the shader to clamp has been removed, and I use this shader a lot now! :) However, the other half of the issue was matching lights/brightness etc, but that's more of an issue with LightWave's shading model for specular hotspots, so that part hasn't been fixed. That is not so much of a 'bug' though :)

No idea if the Oren-Nayer / Diffuse model bug with radiosity has been fixed? I tend not to use the diffuse shader models, as I am mostly using radiosity to light the scene :)
 
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