Since we will be discarding some parts of the teapot, we will be able to see through the teapot to the other side. This will cause the back sides of some polygons to become visible. Therefore, we need to compute the lighting equation appropriately for both sides of each face. We'll use the same technique presented earlier in the two-sided shading recipe.
The vertex shader is essentially the same as in the two-sided shading recipe, with the main difference being the addition of the texture coordinate. To manage the texture coordinate, we have an additional input variable, VertexTexCoord, that corresponds to attribute location 2. The value of this input variable is passed directly on to the fragment shader unchanged via the ...
