diff options
author | mtklein <mtklein@google.com> | 2015-04-21 08:09:30 -0700 |
---|---|---|
committer | Commit bot <commit-bot@chromium.org> | 2015-04-21 08:09:30 -0700 |
commit | a4a0aeb74808a0860f3e94588d0ceb0da9fed386 (patch) | |
tree | df261cb8e23161abffe763002dfa0d650bbcc357 /src/core/SkBlitRow_D32.cpp | |
parent | 8672f4dffa4b298d4cabee6151590ae885d47263 (diff) |
Revert of Convert Color32 code to perfect blend. (patchset #6 id:100001 of https://codereview.chromium.org/1098913002/)
Reason for revert:
Xfermode_SrcOver not looking encouraging. Up to 50% regressions.
https://perf.skia.org/#3242
Original issue's description:
> Convert Color32 code to perfect blend.
>
> Before we commit to blend_256_round_alt, let's make sure blend_perfect is
> really slower in practice (i.e. regresses on perf.skia.org).
>
> blend_perfect is really the most desirable algorithm if we can afford it. Not
> only is it correct, but it's easy to think about and break into correct pieces:
> for instance, its div255() doesn't require any coordination with the multiply.
>
> This looks like a 30% hit according to microbenches. That said, microbenches
> said my previous change would be a 20-25% perf improvement, but it didn't end
> up showing a significant effect at a high level.
>
> As for correctness, I see a bunch of off-by-1 compared to blend_256_round_alt
> (exactly what we'd expect), and one off-by-3 in a GM that looks like it has a
> bunch of overdraw.
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/61221e7f87a99765b0e034020e06bb018e2a08c2
TBR=reed@google.com,fmalita@chromium.org,mtklein@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:
Review URL: https://codereview.chromium.org/1083923006
Diffstat (limited to 'src/core/SkBlitRow_D32.cpp')
-rw-r--r-- | src/core/SkBlitRow_D32.cpp | 27 |
1 files changed, 15 insertions, 12 deletions
diff --git a/src/core/SkBlitRow_D32.cpp b/src/core/SkBlitRow_D32.cpp index 36bfa54095..ac01e427bf 100644 --- a/src/core/SkBlitRow_D32.cpp +++ b/src/core/SkBlitRow_D32.cpp @@ -142,8 +142,11 @@ SkBlitRow::Proc32 SkBlitRow::ColorProcFactory() { #define SK_SUPPORT_LEGACY_COLOR32_MATHx -// Color32 and its SIMD specializations use the blend_perfect algorithm from tests/BlendTest.cpp. -// An acceptable alternative is blend_256_round_alt, which is faster but not quite perfect. +// Color32 and its SIMD specializations use the blend_256_round_alt algorithm +// from tests/BlendTest.cpp. It's not quite perfect, but it's never wrong in the +// interesting edge cases, and it's quite a bit faster than blend_perfect. +// +// blend_256_round_alt is our currently blessed algorithm. Please use it or an analogous one. void SkBlitRow::Color32(SkPMColor* SK_RESTRICT dst, const SkPMColor* SK_RESTRICT src, int count, SkPMColor color) { @@ -153,19 +156,19 @@ void SkBlitRow::Color32(SkPMColor* SK_RESTRICT dst, } unsigned invA = 255 - SkGetPackedA32(color); +#ifdef SK_SUPPORT_LEGACY_COLOR32_MATH // blend_256_plus1_trunc, busted + unsigned round = 0; +#else // blend_256_round_alt, good + invA += invA >> 7; + unsigned round = (128 << 16) + (128 << 0); +#endif + while (count --> 0) { // Our math is 16-bit, so we can do a little bit of SIMD in 32-bit registers. const uint32_t mask = 0x00FF00FF; - uint32_t rb = (((*src >> 0) & mask) * invA), // r_b_ - ag = (((*src >> 8) & mask) * invA); // a_g_ - #ifndef SK_SUPPORT_LEGACY_COLOR32_MATH - uint32_t round = (128 << 16) + (128 << 0); - rb += round; - ag += round; - rb += (rb & ~mask) >> 8; - ag += (ag & ~mask) >> 8; - #endif - *dst = color + (((rb>>8) & mask) | ((ag>>0) & ~mask)); + uint32_t rb = (((*src >> 0) & mask) * invA + round) >> 8, // _r_b + ag = (((*src >> 8) & mask) * invA + round) >> 0; // a_g_ + *dst = color + ((rb & mask) | (ag & ~mask)); src++; dst++; } |