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Question by Jessy · Apr 02, 2010 at 09:06 PM · shaderculling

Does a mesh need normals in order for backface culling to occur?

I kept getting errors about some of my procedural meshes not having normals, despite the "shader wanting them". So I just manually used BindChannels to not deal with the normals. For meshes that are 2D GUI elements, I think that's dandy. However, what if not? Does a "real 3D" mesh require the vertex normals to be bound, for backface culling to happen?

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Answer by Lucas Meijer 1 · Apr 02, 2010 at 11:13 PM

Normals are required by most shaders in order to determine which color to give to each pixel of the triangle. Most shaders do this by comparing the interpolated normal of the three vertices with the direction of the light.

For backface culling, you do not need normals. the "face winding" of the triangle is used. If your triangles happen to be culled "the wrong way around", change the triangle indices from 1,2,3 to 1,3,2

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avatar image Jessy · Apr 04, 2010 at 02:29 AM 0
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Fantastic. I'm not using lights on anything these days, in order to squeeze performance out on the iPhone. Do you know if it will give me any performance gains on everything, if I don't bind the normals? As in, just use BindChannels {"vertex" = vertex; "texcoord" = texcoord} ?

avatar image Lucas Meijer 1 ♦♦ · Apr 04, 2010 at 10:25 AM 0
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Try it :). I suspect not having any normals in your meshdata would help. Then again, the only way is to try.

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