Cache the inverse matrix on SkColorSpace. Rename xyz() to toXYZ().

src/core/SkColorSpace.cpp

Index: src/core/SkColorSpace.cpp
diff --git a/src/core/SkColorSpace.cpp b/src/core/SkColorSpace.cpp
index e6676066bb24beac7ee8125478d1715921829fb9..9885acc0d8d32910312d45b2906fc2586b282dab 100644
--- a/src/core/SkColorSpace.cpp
+++ b/src/core/SkColorSpace.cpp
@@ -19,6 +19,7 @@ SkColorSpace_Base::SkColorSpace_Base(SkGammaNamed gammaNamed, const SkMatrix44&
     , fGammaNamed(gammaNamed)
     , fGammas(nullptr)
     , fProfileData(nullptr)
+    , fFromXYZD50(SkMatrix44::kUninitialized_Constructor)
 {}
 
 SkColorSpace_Base::SkColorSpace_Base(sk_sp<SkColorLookUpTable> colorLUT, SkGammaNamed gammaNamed,
@@ -29,6 +30,7 @@ SkColorSpace_Base::SkColorSpace_Base(sk_sp<SkColorLookUpTable> colorLUT, SkGamma
     , fGammaNamed(gammaNamed)
     , fGammas(std::move(gammas))
     , fProfileData(std::move(profileData))
+    , fFromXYZD50(SkMatrix44::kUninitialized_Constructor)
 {}
 
 static constexpr float gSRGB_toXYZD50[] {
@@ -43,6 +45,18 @@ static constexpr float gAdobeRGB_toXYZD50[] {
     0.1492f, 0.0632f, 0.7448f,    // * B
 };
 
+const SkMatrix44& SkColorSpace_Base::fromXYZ() const {

[msarett, 2016/09/08 15:06:07]

nit: In my head, this should be next to the other "getters" in this file
(gammaIsLinear(), gammaCloseSRGB()).

Does that make sense to anyone else?

+    fFromXYZOnce([this] {
+        if (!fToXYZD50.invert(&fFromXYZD50)) {
+            SkDEBUGFAIL("Non-invertible XYZ matrix, defaulting to sRGB");
+            SkMatrix44 srgbToxyzD50(SkMatrix44::kUninitialized_Constructor);

[msarett, 2016/09/08 15:06:07]

I'm fine with this behavior, but just to be clear on the implications of this:

Every time a client asks for a transform to a dst gamut that we can't invert -
we will instead give them a transform to sRGB gamut.

Maybe a comment?

+            srgbToxyzD50.set3x3RowMajorf(gSRGB_toXYZD50);
+            srgbToxyzD50.invert(&fFromXYZD50);
+        }
+    });
+    return fFromXYZD50;
+}
+
 /**
  *  Checks if our toXYZ matrix is a close match to a known color gamut.
  *