The use as a final 'publication format' for premultiplied alpha is that there is never a reason to have the texel get multiplied by it's own internal values at any time during final use, and in fact a large reason to avoid doing that because such situations tend to break down when (bi/tri/)linear filtering is applied to the texel sources. This is because you can no longer 'correct' for the internal values being affected by each other, as you no longer have exact control over all accessed values in any but the simplest of synthetic cases.
Most of the other 'bennies' are actually side-effects of the fact that it makes multiple passes associative, and that the only other commonly-used texturing mode (additive) can be duplicated with this modified blending mode, which allows for further optimization to suddenly be unlocked. Such as combining the diffuse and 'blend' texturing passes on light fixtures in a Q3 level, for a straight-forward example.
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Date: 2007-04-09 08:51 am (UTC)The use as a final 'publication format' for premultiplied alpha is that there is never a reason to have the texel get multiplied by it's own internal values at any time during final use, and in fact a large reason to avoid doing that because such situations tend to break down when (bi/tri/)linear filtering is applied to the texel sources. This is because you can no longer 'correct' for the internal values being affected by each other, as you no longer have exact control over all accessed values in any but the simplest of synthetic cases.
Most of the other 'bennies' are actually side-effects of the fact that it makes multiple passes associative, and that the only other commonly-used texturing mode (additive) can be duplicated with this modified blending mode, which allows for further optimization to suddenly be unlocked. Such as combining the diffuse and 'blend' texturing passes on light fixtures in a Q3 level, for a straight-forward example.