Relax constraints on src coeff in GrDrawState::willBlendWithDst.

Relax constraints on src coeff in GrDrawState::willBlendWithDst.

Allow the srcCoeff to be anything as long as it does not reference the dst. Previous version
required srcCoeff to be one.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/b1cff03325c42bb1cd87204d9b0dd3d6b9678d3e

[egdaniel, 2014-11-12 20:42:44]

egdaniel@google.com changed reviewers:
+ bsalomon@google.com

[Chris Dalton, 2014-11-12 21:21:48]

cdalton@nvidia.com changed reviewers:
+ cdalton@nvidia.com

[Chris Dalton, 2014-11-12 21:21:49]

Looks like a good change. I have one comment that's only relevant if
srcAlphaWillBeOne is/can be a slow call (I'm not sure if it is in practice.)

https://codereview.chromium.org/718103003/diff/20001/src/gpu/GrDrawState.cpp
File src/gpu/GrDrawState.cpp (right):

https://codereview.chromium.org/718103003/diff/20001/src/gpu/GrDrawState.cpp#...
src/gpu/GrDrawState.cpp:753: bool srcAIsOne = this->srcAlphaWillBeOne();
Just a thought, I'm not too familiar with how slow a call can be to
srcAlphaWillBeOne, but if it's slow enough it may be worth it to only call if
needed -- only when src coefficient is ISA, we know the dst coefficient doesn't
ref the dst, etc. etc. etc.

[bsalomon, 2014-11-12 21:33:38]

https://codereview.chromium.org/718103003/diff/20001/src/gpu/GrDrawState.cpp
File src/gpu/GrDrawState.cpp (right):

https://codereview.chromium.org/718103003/diff/20001/src/gpu/GrDrawState.cpp#...
src/gpu/GrDrawState.cpp:756: if (kISA_GrBlendCoeff == dstCoeff && srcAIsOne) {
At a minimum we can just change this srcAIsOne to this->srcAlphaWillBeOne() and
remove the above line so that it isn't called unless dstCoeff is kISA.

Otherwise, lgtm.

[egdaniel, 2014-11-12 22:06:56]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2014-11-12 22:18:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/718103003/60001

[commit-bot: I haz the power, 2014-11-12 22:58:28]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-11-12 22:58:30]

Try jobs failed on following builders:
  Build-Win-VS2013-x86-Debug-Trybot on client.skia.compile
(http://build.chromium.org/p/client.skia.compile/builders/Build-Win-VS2013-x86...)

[egdaniel, 2014-11-13 14:09:16]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2014-11-13 14:10:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/718103003/60001

[commit-bot: I haz the power, 2014-11-13 14:19:31]

Committed patchset #4 (id:60001) as
https://skia.googlesource.com/skia/+/b1cff03325c42bb1cd87204d9b0dd3d6b9678d3e