Orientation Dependence - Modeling and Rendering
The outcomes of interpolated-shading models are dependent of the projected polygon's orientation. Because values are interpolated among vertices and across horizontal scan lines, the results may be different when the polygon is rotated. This consequence is mainly obvious when the orientation modifies slowly among successive frames of an animation. A same problem cab also happens in visible-surface determination while the z value at each point is interpolated by the z values allocated to each vertex. Both issues can be resolved through decomposing polygons into triangles. Instead, the solution is rotation- independent, although expensive, interpolation methods which solve problem without the requirement for decomposition.