Shader/Renderer Culling

Say I have a solid that’s concave, but split into two different meshes, the outside and the inside section.

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How would I make it so that it renders the inside section like normal, but then cuts out the red section? (like this, explanation is difficult:)

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I’ve tried using a shader that doesn’t render anything but the back of a polygon, but that didn’t work as it still renders the inside of the red mesh and the inside of the grey mesh. I don’t know how to use shaders, so yeah. Any help would be great. This counts as culling right? I don’t even know what to call this, so sorry about the title I guess.

Never mind, found this post here that answers my question. Hope this helps, I guess.