SkColorSpaceXformSteps improvements and tests

Added some helper functions and put the booleans in a nested struct
(this is motivated by upcoming changes). Added a unit test of steps
against skcms, with round-tripping in both combinations.

Change-Id: Iea3d60cd52edb5259b5576b1422ed6f856cde815
Reviewed-on: https://skia-review.googlesource.com/134660
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

2 files changed, 70 insertions, 26 deletions

diff --git a/src/core/SkColorSpaceXformSteps.cpp b/src/core/SkColorSpaceXformSteps.cpp
index a084206aff..ae230ee0fc 100644
--- a/src/core/SkColorSpaceXformSteps.cpp
+++ b/src/core/SkColorSpaceXformSteps.cpp
@@ -17,13 +17,13 @@ SkColorSpaceXformSteps::SkColorSpaceXformSteps(SkColorSpace* src, SkAlphaType sr
     // We have some options about what to do with null src or dst here.
     SkASSERT(src && dst);
 
-    this->unpremul        = srcAT == kPremul_SkAlphaType;
-    this->linearize       = !src->gammaIsLinear();
-    this->gamut_transform = src->toXYZD50Hash() != dst->toXYZD50Hash();
-    this->encode          = !dst->gammaIsLinear();
-    this->premul          = srcAT != kOpaque_SkAlphaType;
+    this->flags.unpremul        = srcAT == kPremul_SkAlphaType;
+    this->flags.linearize       = !src->gammaIsLinear();
+    this->flags.gamut_transform = src->toXYZD50Hash() != dst->toXYZD50Hash();
+    this->flags.encode          = !dst->gammaIsLinear();
+    this->flags.premul          = srcAT != kOpaque_SkAlphaType;
 
-    if (this->gamut_transform && src->toXYZD50() && dst->fromXYZD50()) {
+    if (this->flags.gamut_transform && src->toXYZD50() && dst->fromXYZD50()) {
         auto xform = SkMatrix44(*dst->fromXYZD50(), *src->toXYZD50());
         if (xform.get(3,0) == 0 && xform.get(3,1) == 0 && xform.get(3,2) == 0 &&
             xform.get(3,3) == 1 &&
@@ -31,7 +31,7 @@ SkColorSpaceXformSteps::SkColorSpaceXformSteps(SkColorSpace* src, SkAlphaType sr
 
             for (int r = 0; r < 3; r++)
             for (int c = 0; c < 3; c++) {
-                this->src_to_dst_matrix[3*r+c] = xform.get(r,c);
+                this->src_to_dst_matrix[3*c+r] = xform.get(r,c);
             }
         }
     }
@@ -44,22 +44,54 @@ SkColorSpaceXformSteps::SkColorSpaceXformSteps(SkColorSpace* src, SkAlphaType sr
     this->dstTFInv = dstTF.invert();
 
     // If we linearize then immediately reencode with the same transfer function, skip both.
-    if ( this->linearize       &&
-        !this->gamut_transform &&
-         this->encode          &&
+    if ( this->flags.linearize       &&
+        !this->flags.gamut_transform &&
+         this->flags.encode          &&
         0 == memcmp(&srcTF, &dstTF, sizeof(SkColorSpaceTransferFn)))
     {
-        this->linearize  = false;
-        this->encode     = false;
+        this->flags.linearize  = false;
+        this->flags.encode     = false;
     }
 
     // Skip unpremul...premul if there are no non-linear operations between.
-    if ( this->unpremul   &&
-        !this->linearize  &&
-        !this->encode     &&
-         this->premul)
+    if ( this->flags.unpremul   &&
+        !this->flags.linearize  &&
+        !this->flags.encode     &&
+         this->flags.premul)
     {
-        this->unpremul = false;
-        this->premul   = false;
+        this->flags.unpremul = false;
+        this->flags.premul   = false;
+    }
+}
+
+void SkColorSpaceXformSteps::apply(float* rgba) const {
+    if (flags.unpremul) {
+        float invA = isfinite(1.0f / rgba[3]) ? 1.0f / rgba[3] : 0;
+        rgba[0] *= invA;
+        rgba[1] *= invA;
+        rgba[2] *= invA;
+    }
+    if (flags.linearize) {
+        rgba[0] = srcTF(rgba[0]);
+        rgba[1] = srcTF(rgba[1]);
+        rgba[2] = srcTF(rgba[2]);
+    }
+    if (flags.gamut_transform) {
+        float temp[3] = { rgba[0], rgba[1], rgba[2] };
+        for (int i = 0; i < 3; ++i) {
+            rgba[i] = src_to_dst_matrix[    i] * temp[0] +
+                      src_to_dst_matrix[3 + i] * temp[1] +
+                      src_to_dst_matrix[6 + i] * temp[2];
+        }
+    }
+    if (flags.encode) {
+        rgba[0] = dstTFInv(rgba[0]);
+        rgba[1] = dstTFInv(rgba[1]);
+        rgba[2] = dstTFInv(rgba[2]);
+    }
+    if (flags.premul) {
+        rgba[0] *= rgba[3];
+        rgba[1] *= rgba[3];
+        rgba[2] *= rgba[3];
     }
 }
diff --git a/src/core/SkColorSpaceXformSteps.h b/src/core/SkColorSpaceXformSteps.h
index 6c38411692..3b2a88cddc 100644
--- a/src/core/SkColorSpaceXformSteps.h
+++ b/src/core/SkColorSpaceXformSteps.h
@@ -12,6 +12,22 @@
 #include "SkImageInfo.h"
 
 struct SkColorSpaceXformSteps {
+    struct Flags {
+        bool unpremul;
+        bool linearize;
+        bool gamut_transform;
+        bool encode;
+        bool premul;
+
+        uint32_t mask() const {
+            return (unpremul        ?  1 : 0)
+                 | (linearize       ?  2 : 0)
+                 | (gamut_transform ?  4 : 0)
+                 | (encode          ?  8 : 0)
+                 | (premul          ? 16 : 0);
+        }
+    };
+
     SkColorSpaceXformSteps(SkColorSpace* src, SkAlphaType srcAT,
                            SkColorSpace* dst);
 
@@ -22,17 +38,13 @@ struct SkColorSpaceXformSteps {
         return SkColorSpaceXformSteps(src, kOpaque_SkAlphaType, dst);
     }
 
-    bool unpremul;
-    bool linearize;
-    bool gamut_transform;
-    bool encode;
-    bool premul;
+    void apply(float rgba[4]) const;
+
+    Flags flags;
 
     SkColorSpaceTransferFn srcTF,     // Apply for linearize.
                            dstTFInv;  // Apply for encode.
-    float src_to_dst_matrix[9];       // Apply this 3x3 row-major matrix for gamut_transform.
+    float src_to_dst_matrix[9];       // Apply this 3x3 column-major matrix for gamut_transform.
 };
 
-
-
 #endif//SkColorSpaceXformSteps_DEFINED