Oops, fix an edge case for avoiding discard #11277
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We could end up with the wrong blending in other cases, because the exiting color will get multiplied. Luckily, this is still the common case.
Otherwise we hang because there's no thread to ever end.
It should be equally unsafe to use src color as dest blend factor, or use blending with a subtract or min/max equation.
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Realized that not all the
safeDestFactorswere "safe" for this, since we need to preserve the dest color.I did find
1.0 - src.a,1.0 - 2.0 * src.aandfixed 1.0used, which are all safe. I figure these checks are likely cheap, since drawing with obscure blend factors is fairly uncommon. I didn't actually find unsafe cases, but I'm sure there are a few out there in some special effects...I also replaced the
> 0alpha test trivially true check with the same logic, because I think it's equally unsafe. Considersrc * src.a - dst * src- replacing src.a with 0 is definitely not equivalent to a discard. Luckily, this should only disable the optimization for edge cases.-[Unknown]