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Remember that we choose a map shape and a map entity when texture mapping. When discussing map shape, we talked about taking an (x,y,z) value from the object and converting in various ways, but we didnít mention what that value was. The map entity determines what we use as the (x,y,z) value. Commonly-used map entities are 1) a point on the object relative to the objectís bounding box, 2) the surface normal at the point being rendered, 3) a vector running from the objectís centroid through the point, and 4) the reflection vector at the current point. Remember that the reflection vector depends not only on the position of the point and its normal, but on the position of the viewer.