WIP: Skia support library for ICC tasks

As a starting point, this would be mostly trivial to implement using
SkColorSpace.

This also would give us the flexibility to begin to move all of
the ICC related code from SkColorSpace to SkICC.

What are the advantages of moving this away from SkColorSpace?
(1) A long term goal (once Chrome uses SkCodec), might be to
move SkColorSpace::MakeICC() out of the public API.  That way,
we can guarantee that we can draw to/from *any* SkColorSpace.
(2) Keeps SkColorSpace separate from ICC-specific representations
like SkColorSpaceTransferFn etc.

BUG=skia:

Change-Id: Iddeb9903221fb57fbfc01218d8641c928b4a5165
Reviewed-on: https://skia-review.googlesource.com/5676
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Reed <reed@google.com>

1 files changed, 50 insertions, 1 deletions

diff --git a/src/core/SkColorSpacePriv.h b/src/core/SkColorSpacePriv.h
index 73038738ff..32981ae875 100644
--- a/src/core/SkColorSpacePriv.h
+++ b/src/core/SkColorSpacePriv.h
@@ -5,14 +5,22 @@
  * found in the LICENSE file.
  */
 
+#include <math.h>
+
 #define SkColorSpacePrintf(...)
 
 static inline bool color_space_almost_equal(float a, float b) {
     return SkTAbs(a - b) < 0.01f;
 }
 
+static inline float add_epsilon(float v) {
+    return v + FLT_MIN;
+}
+
 static inline bool is_zero_to_one(float v) {
-    return (0.0f <= v) && (v <= 1.0f);
+    // Because we allow a value just barely larger than 1, the client can use an
+    // entirely linear transfer function.
+    return (0.0f <= v) && (v <= add_epsilon(1.0f));
 }
 
 static inline bool is_valid_transfer_fn(const SkColorSpaceTransferFn& coeffs) {
@@ -84,3 +92,44 @@ static inline bool is_almost_2dot2(const SkColorSpaceTransferFn& coeffs) {
            color_space_almost_equal(0.0f, coeffs.fF) &&
            color_space_almost_equal(2.2f, coeffs.fG);
 }
+
+static inline void value_to_parametric(SkColorSpaceTransferFn* coeffs, float exponent) {
+    coeffs->fA = 1.0f;
+    coeffs->fB = 0.0f;
+    coeffs->fC = 0.0f;
+    coeffs->fD = 0.0f;
+    coeffs->fE = 0.0f;
+    coeffs->fF = 0.0f;
+    coeffs->fG = exponent;
+}
+
+static inline bool named_to_parametric(SkColorSpaceTransferFn* coeffs,
+                                       SkGammaNamed gammaNamed) {
+    switch (gammaNamed) {
+        case kSRGB_SkGammaNamed:
+            coeffs->fA = 1.0f / 1.055f;
+            coeffs->fB = 0.055f / 1.055f;
+            coeffs->fC = 0.0f;
+            coeffs->fD = 0.04045f;
+            coeffs->fE = 1.0f / 12.92f;
+            coeffs->fF = 0.0f;
+            coeffs->fG = 2.4f;
+            return true;
+        case k2Dot2Curve_SkGammaNamed:
+            value_to_parametric(coeffs, 2.2f);
+            return true;
+        case kLinear_SkGammaNamed:
+            coeffs->fA = 0.0f;
+            coeffs->fB = 0.0f;
+            coeffs->fC = 0.0f;
+            // Make sure that we use the linear segment of the transfer function even
+            // when the x-value is 1.0f.
+            coeffs->fD = add_epsilon(1.0f);
+            coeffs->fE = 1.0f;
+            coeffs->fF = 0.0f;
+            coeffs->fG = 0.0f;
+            return true;
+        default:
+            return false;
+    }
+}