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

src/core/SkColorSpace.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkColorSpace.h"
 #include "SkColorSpace_Base.h"
 #include "SkColorSpacePriv.h"
 #include "SkOnce.h"
 
 SkColorSpace::SkColorSpace(const SkMatrix44& toXYZD50)
     : fToXYZD50(toXYZD50)
 {}
 
 SkColorSpace_Base::SkColorSpace_Base(SkGammaNamed gammaNamed, const SkMatrix44& toXYZD50)
     : INHERITED(toXYZD50)
     , fGammaNamed(gammaNamed)
     , fGammas(nullptr)
     , fProfileData(nullptr)
+    , fFromXYZD50(SkMatrix44::kUninitialized_Constructor)
 {}
 
 SkColorSpace_Base::SkColorSpace_Base(sk_sp<SkColorLookUpTable> colorLUT, SkGammaNamed gammaNamed,
                                      sk_sp<SkGammas> gammas, const SkMatrix44& toXYZD50,
                                      sk_sp<SkData> profileData)
     : INHERITED(toXYZD50)
     , fColorLUT(std::move(colorLUT))
     , fGammaNamed(gammaNamed)
     , fGammas(std::move(gammas))
     , fProfileData(std::move(profileData))
+    , fFromXYZD50(SkMatrix44::kUninitialized_Constructor)
 {}
 
 static constexpr float gSRGB_toXYZD50[] {
     0.4358f, 0.2224f, 0.0139f,    // * R
     0.3853f, 0.7170f, 0.0971f,    // * G
     0.1430f, 0.0606f, 0.7139f,    // * B
 };
 
 static constexpr float gAdobeRGB_toXYZD50[] {
     0.6098f, 0.3111f, 0.0195f,    // * R
@@ skipping 133 matching lines @@
 
 bool SkColorSpace::gammaCloseToSRGB() const {
     return kSRGB_SkGammaNamed == as_CSB(this)->fGammaNamed ||
            k2Dot2Curve_SkGammaNamed == as_CSB(this)->fGammaNamed;
 }
 
 bool SkColorSpace::gammaIsLinear() const {
     return kLinear_SkGammaNamed == as_CSB(this)->fGammaNamed;
 }
 
+const SkMatrix44& SkColorSpace_Base::fromXYZD50() const {
+    fFromXYZOnce([this] {
+        if (!fToXYZD50.invert(&fFromXYZD50)) {
+            // If a client gives us a dst gamut with a transform that we can't invert, we will
+            // simply give them back a transform to sRGB gamut.
+            SkDEBUGFAIL("Non-invertible XYZ matrix, defaulting to sRGB");
+            SkMatrix44 srgbToxyzD50(SkMatrix44::kUninitialized_Constructor);
+            srgbToxyzD50.set3x3RowMajorf(gSRGB_toXYZD50);
+            srgbToxyzD50.invert(&fFromXYZD50);
+        }
+    });
+    return fFromXYZD50;
+}
+
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 enum Version {
     k0_Version, // Initial version, header + flags for matrix and profile
 };
 
 struct ColorSpaceHeader {
     /**
      *  If kMatrix_Flag is set, we will write 12 floats after the header.
      *  Should not be set at the same time as the kICC_Flag or kFloatGamma_Flag.
@@ skipping 226 matching lines @@
                 return false;
             }
 
             // It is unlikely that we will reach this case.
             sk_sp<SkData> srcData = src->serialize();
             sk_sp<SkData> dstData = dst->serialize();
             return srcData->size() == dstData->size() &&
                    0 == memcmp(srcData->data(), dstData->data(), srcData->size());
     }
 }