Factor text size device mapping in SkScalerContext.

src/ports/SkScalerContext_win_dw.cpp

Index: src/ports/SkScalerContext_win_dw.cpp
diff --git a/src/ports/SkScalerContext_win_dw.cpp b/src/ports/SkScalerContext_win_dw.cpp
index f3f371c878aba8e06b6954280d742c8479d7adb5..1e10e174c0bb8596171dcecfa8a9e54a4bfc89fa 100644
--- a/src/ports/SkScalerContext_win_dw.cpp
+++ b/src/ports/SkScalerContext_win_dw.cpp
@@ -210,26 +210,29 @@ SkScalerContext_DW::SkScalerContext_DW(DWriteFontTypeface* typeface,
     // Also, rotated glyphs should have the same absolute advance widths as
     // horizontal glyphs and the subpixel flag should not affect glyph shapes.
 
-    // A is the total matrix.
-    SkMatrix A;
-    fRec.getSingleMatrix(&A);
+    SkVector scale;
+    SkMatrix GsA;
+    fRec.computeMatrices(SkScalerContextRec::kVertical_PreMatrixScale,
+                         &scale, &fSkXform, &GsA, &fG_inv);
 
-    // h is where A maps the horizontal baseline.
-    SkPoint h = SkPoint::Make(SK_Scalar1, 0);
-    A.mapPoints(&h, 1);
-
-    // G is the Givens Matrix for A (rotational matrix where GA[0][1] == 0).
-    SkMatrix G;
-    SkComputeGivensRotation(h, &G);
+    fXform.m11 = SkScalarToFloat(fSkXform.getScaleX());
+    fXform.m12 = SkScalarToFloat(fSkXform.getSkewY());
+    fXform.m21 = SkScalarToFloat(fSkXform.getSkewX());
+    fXform.m22 = SkScalarToFloat(fSkXform.getScaleY());
+    fXform.dx = 0;
+    fXform.dy = 0;
 
-    // GA is the matrix A with rotation removed.
-    SkMatrix GA(G);
-    GA.preConcat(A);
+    fGsA.m11 = SkScalarToFloat(GsA.get(SkMatrix::kMScaleX));
+    fGsA.m12 = SkScalarToFloat(GsA.get(SkMatrix::kMSkewY)); // This should be ~0.
+    fGsA.m21 = SkScalarToFloat(GsA.get(SkMatrix::kMSkewX));
+    fGsA.m22 = SkScalarToFloat(GsA.get(SkMatrix::kMScaleY));
+    fGsA.dx = 0;
+    fGsA.dy = 0;
 
     // realTextSize is the actual device size we want (as opposed to the size the user requested).
     // gdiTextSize is the size we request when GDI compatible.
     // If the scale is negative, this means the matrix will do the flip anyway.
-    SkScalar realTextSize = SkScalarAbs(GA.get(SkMatrix::kMScaleY));
+    const SkScalar realTextSize = scale.fY;
     // Due to floating point math, the lower bits are suspect. Round carefully.
     SkScalar gdiTextSize = SkScalarRoundToScalar(realTextSize * 64.0f) / 64.0f;
     if (gdiTextSize == 0) {
@@ -300,36 +303,6 @@ SkScalerContext_DW::SkScalerContext_DW(DWriteFontTypeface* typeface,
         fTextSizeMeasure = realTextSize;
         fMeasuringMode = DWRITE_MEASURING_MODE_NATURAL;
     }
-
-    // Remove the realTextSize, as that is the text height scale currently in A.
-    SkScalar scale = SkScalarInvert(realTextSize);
-
-    // fSkXform is the total matrix A without the text height scale.
-    fSkXform = A;
-    fSkXform.preScale(scale, scale); //remove the text height scale.
-
-    fXform.m11 = SkScalarToFloat(fSkXform.getScaleX());
-    fXform.m12 = SkScalarToFloat(fSkXform.getSkewY());
-    fXform.m21 = SkScalarToFloat(fSkXform.getSkewX());
-    fXform.m22 = SkScalarToFloat(fSkXform.getScaleY());
-    fXform.dx = 0;
-    fXform.dy = 0;
-
-    // GsA is the non-rotational part of A without the text height scale.
-    SkMatrix GsA(GA);
-    GsA.preScale(scale, scale); //remove text height scale, G is rotational so reorders with scale.
-
-    fGsA.m11 = SkScalarToFloat(GsA.get(SkMatrix::kMScaleX));
-    fGsA.m12 = SkScalarToFloat(GsA.get(SkMatrix::kMSkewY)); // This should be ~0.
-    fGsA.m21 = SkScalarToFloat(GsA.get(SkMatrix::kMSkewX));
-    fGsA.m22 = SkScalarToFloat(GsA.get(SkMatrix::kMScaleY));
-    fGsA.dx = 0;
-    fGsA.dy = 0;
-
-    // fG_inv is G inverse, which is fairly simple since G is 2x2 rotational.
-    fG_inv.setAll(G.get(SkMatrix::kMScaleX), -G.get(SkMatrix::kMSkewX), G.get(SkMatrix::kMTransX),
-                  -G.get(SkMatrix::kMSkewY), G.get(SkMatrix::kMScaleY), G.get(SkMatrix::kMTransY),
-                  G.get(SkMatrix::kMPersp0), G.get(SkMatrix::kMPersp1), G.get(SkMatrix::kMPersp2));
 }
 
 SkScalerContext_DW::~SkScalerContext_DW() {