SkColorCubeFilter: require alpha == 0xFF.

src/opts/SkPMFloat_sse.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 namespace {  // See SkPMFloat.h
 
 inline SkPMFloat::SkPMFloat(SkPMColor c) {
@@ skipping 20 matching lines @@
     SkPMColor c = _mm_cvtsi128_si32(fix8);
     SkPMColorAssert(c);
     return c;
 }
 
 inline Sk4f SkPMFloat::alphas() const {
     static_assert(SK_A32_SHIFT == 24, "");
     return _mm_shuffle_ps(fVec, fVec, 0xff);  // Read as 11 11 11 11, copying lane 3 to all lanes.
 }
 
-inline SkPMFloat SkPMFloat::FromBGRx(SkColor c) {
+inline SkPMFloat SkPMFloat::FromOpaqueColor(SkColor c) {
+    SkASSERT(SkColorGetA(c) == 0xFF);
     __m128i fix8 = _mm_cvtsi32_si128((int)c);
 #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSSE3
     const char _ = ~0;  // Zero these bytes.
     __m128i fix8_32 = _mm_shuffle_epi8(fix8,
     #if defined(SK_PMCOLOR_IS_BGRA)
-            _mm_setr_epi8(0,_,_,_, 1,_,_,_, 2,_,_,_, _,_,_,_)
+            _mm_setr_epi8(0,_,_,_, 1,_,_,_, 2,_,_,_, 3,_,_,_)
     #else
-            _mm_setr_epi8(2,_,_,_, 1,_,_,_, 0,_,_,_, _,_,_,_)
+            _mm_setr_epi8(2,_,_,_, 1,_,_,_, 0,_,_,_, 3,_,_,_)
     #endif
     );
 #else
     __m128i fix8_16 = _mm_unpacklo_epi8 (fix8   , _mm_setzero_si128()),
             fix8_32 = _mm_unpacklo_epi16(fix8_16, _mm_setzero_si128());
     #if defined(SK_PMCOLOR_IS_RGBA)
         fix8_32 = _mm_shuffle_epi32(fix8_32, 0xC6);  // C6 == 11 00 01 10, i.e swap lanes 0 and 2.
     #endif
 #endif
-    fix8_32 = _mm_or_si128(fix8_32, _mm_set_epi32(0xFF,0,0,0));  // Force alpha to 1.

[Noel Gordon, 2015/08/20 01:43:29]

Very cool; less instructions generally means more perf.

Aside: there is one other way I've thought of implementing this entire function:

const __m128 __color = _mm_set_ps((float)SkColorGetR(c), (float)SkColorGetR(g),
(float)SkColorGetB(c), 1.0f);  // FIXME
SkPMFloat pmf = Sk4f(_mm_mul_ps(__color, _mm_set1_ps(1.0f/255)));
SkASSERT(pmf.isValid());	
return pmf;

Would need a fix to get the __color R G B byte order correct for platform
PMColor order.  But with many fewer SSE instructions, it might be faster, or it
might not -- it would depend on the latency of _mm_set_ps() and maybe the C++
compiler.

[mtklein, 2015/08/20 01:55:17]

Yeah, _mm_set_ps doesn't really correspond to any particular instruction, so
I've always preferred writing things out myself rather than having to hope GCC,
Clang, and MSVC all generate something good.  But it's worth trying out.  If we
find we can trust _mm_set_ps, it'd make lots of code quite a bit clearer.

I'm not particularly optimistic about this one though, as it'd involve three
cvtsi2ss calls rather than a single cvtdq2ps, and a bunch of serial shifts to
move components around.

-
     SkPMFloat pmf = Sk4f(_mm_mul_ps(_mm_cvtepi32_ps(fix8_32), _mm_set1_ps(1.0f/255)));
     SkASSERT(pmf.isValid());
     return pmf;
 }
 
 }  // namespace