We can avoid the extra normalization needed to compute the vector towards the viewer (v) by using a so-called nonlocal viewer. Instead of computing the direction toward the origin, we simply use the constant vector (0, 0, 1) for all vertices. Of course, it is not accurate, but in practice the visual results are very similar, often visually indistinguishable, saving us one normalization.
Using a nonlocal viewer
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