Add SkColorSpace::isSRGB()

BUG=skia:

Change-Id: I124480a15e0c3cb01f4e22397c0a116f2d1c0d7d
Reviewed-on: https://skia-review.googlesource.com/9239
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Matt Sarett <msarett@google.com>

3 files changed, 40 insertions, 0 deletions

diff --git a/include/core/SkColorSpace.h b/include/core/SkColorSpace.h
index 978660b135..c945703549 100644
--- a/include/core/SkColorSpace.h
+++ b/include/core/SkColorSpace.h
@@ -106,6 +106,8 @@ public:
 
     /**
      *  Returns true if the color space gamma is near enough to be approximated as sRGB.
+     *  This includes the canonical sRGB transfer function as well as a 2.2f exponential
+     *  transfer function.
      */
     bool gammaCloseToSRGB() const;
 
@@ -129,6 +131,20 @@ public:
     bool toXYZD50(SkMatrix44* toXYZD50) const;
 
     /**
+     *  Returns true if the color space is sRGB.
+     *  Returns false otherwise.
+     *
+     *  This allows a little bit of tolerance, given that we might see small numerical error
+     *  in some cases: converting ICC fixed point to float, converting white point to D50,
+     *  rounding decisions on transfer function and matrix.
+     *
+     *  This does not consider a 2.2f exponential transfer function to be sRGB.  While these
+     *  functions are similar (and it is sometimes useful to consider them together), this
+     *  function checks for logical equality.
+     */
+    bool isSRGB() const;
+
+    /**
      *  Returns nullptr on failure.  Fails when we fallback to serializing ICC data and
      *  the data is too large to serialize.
      */
diff --git a/src/core/SkColorSpace.cpp b/src/core/SkColorSpace.cpp
index e059bebc99..3677fb6342 100644
--- a/src/core/SkColorSpace.cpp
+++ b/src/core/SkColorSpace.cpp
@@ -299,6 +299,10 @@ bool SkColorSpace::toXYZD50(SkMatrix44* toXYZD50) const {
     return false;
 }
 
+bool SkColorSpace::isSRGB() const {
+    return gSRGB == this || gSRGBNonLinearBlending == this;
+}
+
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 sk_sp<SkColorSpace> SkColorSpace_Base::makeWithoutFlags() {
diff --git a/tests/ColorSpaceTest.cpp b/tests/ColorSpaceTest.cpp
index 73a49807f3..059fa591fa 100644
--- a/tests/ColorSpaceTest.cpp
+++ b/tests/ColorSpaceTest.cpp
@@ -478,3 +478,23 @@ DEF_TEST(ColorSpace_MatrixHash, r) {
     REPORTER_ASSERT(r, *as_CSB(srgb)->toXYZD50() == *as_CSB(strange)->toXYZD50());
     REPORTER_ASSERT(r, as_CSB(srgb)->toXYZD50Hash() == as_CSB(strange)->toXYZD50Hash());
 }
+
+DEF_TEST(ColorSpace_IsSRGB, r) {
+    sk_sp<SkColorSpace> srgb0 = SkColorSpace::MakeSRGB();
+    sk_sp<SkColorSpace> srgb1 = SkColorSpace::MakeRGB(SkColorSpace::kSRGB_RenderTargetGamma,
+            SkColorSpace::kSRGB_Gamut, SkColorSpace::kNonLinearBlending_ColorSpaceFlag);
+
+    SkColorSpaceTransferFn fn;
+    fn.fA = 1.0f;
+    fn.fB = 0.0f;
+    fn.fC = 0.0f;
+    fn.fD = 0.0f;
+    fn.fE = 0.0f;
+    fn.fF = 0.0f;
+    fn.fG = 2.2f;
+    sk_sp<SkColorSpace> twoDotTwo = SkColorSpace::MakeRGB(fn, SkColorSpace::kSRGB_Gamut);
+
+    REPORTER_ASSERT(r, srgb0->isSRGB());
+    REPORTER_ASSERT(r, srgb1->isSRGB());
+    REPORTER_ASSERT(r, !twoDotTwo->isSRGB());
+}