Energy-Conserving Phong Specular Lobe

Practical and theoretical implementation discussion.
Geometrian
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Re: Energy-Conserving Phong Specular Lobe

Postby Geometrian » Tue Jun 24, 2014 11:29 pm

ypoissant wrote:You are using a hemispherical source so the reflected radiance should never go higher than 0.5. But it can go lower. The Phong lobe is oriented around the reflection vector. So the reflection hemisphere is not oriented around the surface normal. In other words, the reflection sampling hemisphere is not coincident with the light source hemisphere. This means that some samples will go under the macrosurface and contribute nothing by not hitting the hemispherical light source. Suppose the reflection ray is 90° from the surface normal. Then 50% of the reflected rays will go under the macrosurface.
Ah, I think I see. I meant not that I want to conserve energy (although obviously I want that too), but that, more specifically, I don't want absorption of any kind to remove any of the energy incident to the surface.

The scenario you describe is a form of absorption, since those samples are zeroed. I realize that this might possibly be more physically realistic and might possibly be desirable, but in this case right now I don't want it. The reflection-into-the-surface can be disallowed by rejecting those samples as usual, but then scaling the rest of them to compensate.


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