Texture coordinates are linearly interpolated across a tringle.
In case you use a perspective view you have to add a perspective correction which depends on your field of view.
Sorry I don’t see the relation with my question…
Maybe I should re-formulate:
For each vertex of my model I have a texture coordinate. How can I get the RGBA color of the texture at that particular texture coordinate ? is there an openGL function that can do that (but I failed to find it in the red book) ?
Ok, texture coordinates are (usally) normalized between zero and one.
Given a texture of 256x256 the following is true:
-texture coordinate 0.0, 0.0 is the texel 0,0 in the texture.
-texture coordinate 1.0, 1.0 is the texel 256, 256.
-texture coordinate 0.5, 0.5 is the texel 128, 128.