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JohnnyCode

lit sphere shader

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I tried to google this topic, and nothing comes out. I would like to know wheather some of you know about this topic anything, and could explain the principels of this shading technique. This technique primises to create shadows on a geometry without a light being present. I cannot imagine how though.

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Yeah, like about only 60000 hits.

 

Looks like using the view normal to lookup into a spherical texture.

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Yeah, like about only 60000 hits.

 

Looks like using the view normal to lookup into a spherical texture.

 

Yeah, I'm pretty sure it's ultimately identical to any other kind of environment mapping (cube mapping, sphere mapping, etc.) in that it's ultimately just a function that maps angle to color. The only advantage I see is that it represents the function in a fairly intuitive way (and it's easy to capture from paintings, photographs, etc. of a spherical object) and that it stores the most resolution for angles that point toward the camera. The disadvantage is that it's actually only half of an environment map.

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You may also try searching the term "MatCap" or "Material Capture" as this is very similar (if not the same) as that. Render your lights and material to a sphere, then use that resulting image as your lighting environment. Essentially you are precomputing light+material interaction for lights fixed to the viewpoint.

 

http://cgcookie.com/unity/2013/02/18/introduction-to-matcaps-in-unity/

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this seems extremly limiting though. I thought lit sphere is some sort of universal lightless geometry shading without texture resources involved.

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I guess so. And no, it's texture based (not a cubemap, but, erm, dunno, hemisphere map probably). I had to play with this. Here I found the texture I used. There's also a link to a paper. The shader is a bit weird, I think it has to be wired up for that tool Fusion.

Anyway. Using the view space normal on a sphere (here visualized)
683173279495876.jpg
yields the hemisphere map itself.
affad8279495874.jpg

Using a better model
6b9c0f279495871.jpg

Hmmm, nice:
6a9c82279495869.jpg

The shader is quite simple. Ignore z of the view space normal and bring it into texture space.
float2 tex = float2(normal.x, -normal.y) * 0.5 + 0.5;
return LookupTexture.Sample(Sampler, tex);
Doesn't work that great for a moving camera. The light moves with you. Also this texture has bumps which produces very noticable artifacts. Yeah, limiting, but also very cheap. Could be useful for a fixed camera e.g. some 2.5-D setup I guess.

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