Implement fast, correct gamma conversion for color xforms

src/core/SkOpts.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.
  */
 
 #ifndef SkOpts_DEFINED
 #define SkOpts_DEFINED
 
@@ skipping 51 matching lines @@
                         inverted_CMYK_to_RGB1, // i.e. convert color space
                         inverted_CMYK_to_BGR1; // i.e. convert color space
 
     extern void (*half_to_float)(float[], const uint16_t[], int);
     extern void (*float_to_half)(uint16_t[], const float[], int);
 
     // Blend ndst src pixels over dst, where both src and dst point to sRGB pixels (RGBA or BGRA).
     // If nsrc < ndst, we loop over src to create a pattern.
     extern void (*srcover_srgb_srgb)(uint32_t* dst, const uint32_t* src, int ndst, int nsrc);
 
-    // Color xform RGBA input into SkPMColor ordered 8888 pixels.  Does not premultiply, and
-    // assumes src and dst gamma curves are both 2.2f exponentials.
-    extern void (*color_xform_2Dot2_RGBA_to_8888)(uint32_t* dst, const uint32_t* src, int len,
-                                                  const float srcToDstMatrix[16]);
+    // Color xform RGB1 input into SkPMColor ordered 8888 opaque pixels.

[mtklein_C, 2016/06/16 13:27:40]

Doesn't this actually transform RGBA into RGB1 pixels now?  It's only because
you've swapped around the matrix that we get SkPMColor out, right?

[mtklein, 2016/06/16 13:29:28]

Err, RGB1 -> RGB1.  Just interested in color order here, not alpha.

[msarett, 2016/06/16 15:46:11]

Yes fixing this comment.

+    extern void (*color_xform_RGB1_srgb_to_2dot2) (uint32_t* dst, const uint32_t* src, int len,
+                                                   const float srcToDstMatrix[16]);
+    extern void (*color_xform_RGB1_2dot2_to_2dot2)(uint32_t* dst, const uint32_t* src, int len,
+                                                   const float srcToDstMatrix[16]);
 }
 
 #endif//SkOpts_DEFINED