Add SkColorSpacePrimaries to help with making D50 matrices

src/codec/SkPngCodec.cpp

Index: src/codec/SkPngCodec.cpp
diff --git a/src/codec/SkPngCodec.cpp b/src/codec/SkPngCodec.cpp
index 1f3a8d96a44a8aa347813775cd239fd8e8afb2ed..d69cf0f20580eaf83153bd39ede309660779f89c 100644
--- a/src/codec/SkPngCodec.cpp
+++ b/src/codec/SkPngCodec.cpp
@@ -322,63 +322,6 @@ static constexpr float gSRGB_toXYZD50[] {
     0.0139f, 0.0971f, 0.7139f,    // Rz, Gz, Bz
 };
 
-static bool convert_to_D50(SkMatrix44* toXYZD50, float toXYZ[9], float whitePoint[2]) {
-    float wX = whitePoint[0];
-    float wY = whitePoint[1];
-    if (wX < 0.0f || wY < 0.0f || (wX + wY > 1.0f)) {
-        return false;
-    }
-
-    // Calculate the XYZ illuminant.  Call this the src illuminant.
-    float wZ = 1.0f - wX - wY;
-    float scale = 1.0f / wY;
-    // TODO (msarett):
-    // What are common src illuminants?  I'm guessing we will almost always see D65.  Should
-    // we go ahead and save a precomputed D65->D50 Bradford matrix?  Should we exit early if
-    // if the src illuminant is D50?
-    SkVector3 srcXYZ = SkVector3::Make(wX * scale, 1.0f, wZ * scale);
-
-    // The D50 illuminant.
-    SkVector3 dstXYZ = SkVector3::Make(0.96422f, 1.0f, 0.82521f);
-
-    // Calculate the chromatic adaptation matrix.  We will use the Bradford method, thus
-    // the matrices below.  The Bradford method is used by Adobe and is widely considered
-    // to be the best.
-    // http://www.brucelindbloom.com/index.html?Eqn_ChromAdapt.html
-    SkMatrix mA, mAInv;
-    mA.setAll(0.8951f, 0.2664f, -0.1614f, -0.7502f, 1.7135f, 0.0367f, 0.0389f, -0.0685f, 1.0296f);
-    mAInv.setAll(0.9869929f, -0.1470543f, 0.1599627f, 0.4323053f, 0.5183603f, 0.0492912f,
-                 -0.0085287f, 0.0400428f, 0.9684867f);
-
-    // Map illuminant into cone response domain.
-    SkVector3 srcCone;
-    srcCone.fX = mA[0] * srcXYZ.fX + mA[1] * srcXYZ.fY + mA[2] * srcXYZ.fZ;
-    srcCone.fY = mA[3] * srcXYZ.fX + mA[4] * srcXYZ.fY + mA[5] * srcXYZ.fZ;
-    srcCone.fZ = mA[6] * srcXYZ.fX + mA[7] * srcXYZ.fY + mA[8] * srcXYZ.fZ;
-    SkVector3 dstCone;
-    dstCone.fX = mA[0] * dstXYZ.fX + mA[1] * dstXYZ.fY + mA[2] * dstXYZ.fZ;
-    dstCone.fY = mA[3] * dstXYZ.fX + mA[4] * dstXYZ.fY + mA[5] * dstXYZ.fZ;
-    dstCone.fZ = mA[6] * dstXYZ.fX + mA[7] * dstXYZ.fY + mA[8] * dstXYZ.fZ;
-
-    SkMatrix DXToD50;
-    DXToD50.setIdentity();
-    DXToD50[0] = dstCone.fX / srcCone.fX;
-    DXToD50[4] = dstCone.fY / srcCone.fY;
-    DXToD50[8] = dstCone.fZ / srcCone.fZ;
-    DXToD50.postConcat(mAInv);
-    DXToD50.preConcat(mA);
-
-    SkMatrix toXYZ3x3;
-    toXYZ3x3.setAll(toXYZ[0], toXYZ[3], toXYZ[6], toXYZ[1], toXYZ[4], toXYZ[7], toXYZ[2], toXYZ[5],
-                    toXYZ[8]);
-    toXYZ3x3.postConcat(DXToD50);
-
-    toXYZD50->set3x3(toXYZ3x3[0], toXYZ3x3[3], toXYZ3x3[6],
-                     toXYZ3x3[1], toXYZ3x3[4], toXYZ3x3[7],
-                     toXYZ3x3[2], toXYZ3x3[5], toXYZ3x3[8]);
-    return true;
-}
-
 #endif // LIBPNG >= 1.6
 
 // Returns a colorSpace object that represents any color space information in
@@ -416,26 +359,24 @@ sk_sp<SkColorSpace> read_color_space(png_structp png_ptr, png_infop info_ptr) {
     }
 
     // Next, check for chromaticities.
-    png_fixed_point toXYZFixed[9];
-    float toXYZ[9];
-    png_fixed_point whitePointFixed[2];
-    float whitePoint[2];
+    png_fixed_point chrm[8];
     png_fixed_point gamma;
     float gammas[3];
-    if (png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &toXYZFixed[0], &toXYZFixed[1], &toXYZFixed[2],
-                               &toXYZFixed[3], &toXYZFixed[4], &toXYZFixed[5], &toXYZFixed[6],
-                               &toXYZFixed[7], &toXYZFixed[8]) &&
-        png_get_cHRM_fixed(png_ptr, info_ptr, &whitePointFixed[0], &whitePointFixed[1], nullptr,
-                           nullptr, nullptr, nullptr, nullptr, nullptr))
+    if (png_get_cHRM_fixed(png_ptr, info_ptr, &chrm[0], &chrm[1], &chrm[2], &chrm[3], &chrm[4],
+                           &chrm[5], &chrm[6], &chrm[7]))
     {
-        for (int i = 0; i < 9; i++) {
-            toXYZ[i] = png_fixed_point_to_float(toXYZFixed[i]);
-        }
-        whitePoint[0] = png_fixed_point_to_float(whitePointFixed[0]);
-        whitePoint[1] = png_fixed_point_to_float(whitePointFixed[1]);
+        SkColorSpacePrimaries primaries;
+        primaries.fRX = png_fixed_point_to_float(chrm[2]);
+        primaries.fRY = png_fixed_point_to_float(chrm[3]);
+        primaries.fGX = png_fixed_point_to_float(chrm[4]);
+        primaries.fGY = png_fixed_point_to_float(chrm[5]);
+        primaries.fBX = png_fixed_point_to_float(chrm[6]);
+        primaries.fBY = png_fixed_point_to_float(chrm[7]);
+        primaries.fWX = png_fixed_point_to_float(chrm[0]);
+        primaries.fWY = png_fixed_point_to_float(chrm[1]);
 
         SkMatrix44 toXYZD50(SkMatrix44::kUninitialized_Constructor);
-        if (!convert_to_D50(&toXYZD50, toXYZ, whitePoint)) {
+        if (!primaries.toXYZD50(&toXYZD50)) {
             toXYZD50.set3x3RowMajorf(gSRGB_toXYZD50);
         }