Factor text size device mapping in SkScalerContext.

src/ports/SkFontHost_win.cpp

Index: src/ports/SkFontHost_win.cpp
diff --git a/src/ports/SkFontHost_win.cpp b/src/ports/SkFontHost_win.cpp
index 7c0e3ffc252b842d437d825f141e2617e480a40f..5ea55bd7a43b5f5399e003c426359e5afbfcb927 100755
--- a/src/ports/SkFontHost_win.cpp
+++ b/src/ports/SkFontHost_win.cpp
@@ -617,55 +617,27 @@ SkScalerContext_GDI::SkScalerContext_GDI(SkTypeface* rawTypeface,
     SetGraphicsMode(fDDC, GM_ADVANCED);
     SetBkMode(fDDC, TRANSPARENT);
 
-    SkPoint h = SkPoint::Make(SK_Scalar1, 0);
-    // A is the total matrix.
-    SkMatrix A;
-    fRec.getSingleMatrix(&A);
-    A.mapPoints(&h, 1);
-
-    // G is the Givens Matrix for A (rotational matrix where GA[0][1] == 0).
-    SkMatrix G;
-    SkComputeGivensRotation(h, &G);
-
-    // GA is the matrix A with rotation removed.
-    SkMatrix GA(G);
-    GA.preConcat(A);
-
-    // realTextSize is the actual device size we want (as opposed to the size the user requested).
-    // gdiTextSize is the size we request from GDI.
-    // If the scale is negative, this means the matrix will do the flip anyway.
-    SkScalar realTextSize = SkScalarAbs(GA.get(SkMatrix::kMScaleY));
-    SkScalar gdiTextSize = SkScalarRoundToScalar(realTextSize);
-    if (gdiTextSize == 0) {
-        gdiTextSize = SK_Scalar1;
-    }
-
-    // When not hinting, remove only the gdiTextSize scale which will be applied by GDI.
     // When GDI hinting, remove the entire Y scale to prevent 'subpixel' metrics.
-    SkScalar scale = (fRec.getHinting() == SkPaint::kNo_Hinting ||
-                      fRec.getHinting() == SkPaint::kSlight_Hinting)
-                   ? SkScalarInvert(gdiTextSize)
-                   : SkScalarInvert(realTextSize);
-
-    // sA is the total matrix A without the textSize (so GDI knows the text size separately).
-    // When this matrix is used with GetGlyphOutline, no further processing is needed.
-    SkMatrix sA(A);
-    sA.preScale(scale, scale); //remove text size
-
-    // GsA is the non-rotational part of A without the text height scale.
-    // This is what is used to find the magnitude of advances.
-    SkMatrix GsA(GA);
-    GsA.preScale(scale, scale); //remove text size, G is rotational so reorders with the scale.
+    // When not hinting, remove only the gdiTextSize scale which will be applied by GDI.
+    SkScalerContextRec::PreMatrixScale scaleConstraints =
+        (fRec.getHinting() == SkPaint::kNo_Hinting || fRec.getHinting() == SkPaint::kSlight_Hinting)
+                   ? SkScalerContextRec::kVerticalInteger_PreMatrixScale
+                   : SkScalerContextRec::kVertical_PreMatrixScale;
+    SkVector scale;
+    SkMatrix sA;
+    SkMatrix GsA;
+    SkMatrix A;
+    fRec.computeMatrices(scaleConstraints, &scale, &sA, &GsA, &fG_inv, &A);
 
     fGsA.eM11 = SkScalarToFIXED(GsA.get(SkMatrix::kMScaleX));
     fGsA.eM12 = SkScalarToFIXED(-GsA.get(SkMatrix::kMSkewY)); // This should be ~0.
     fGsA.eM21 = SkScalarToFIXED(-GsA.get(SkMatrix::kMSkewX));
     fGsA.eM22 = SkScalarToFIXED(GsA.get(SkMatrix::kMScaleY));
 
-    // 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));
+    SkScalar gdiTextSize = scale.fY;

[bungeman-skia, 2015/03/17 21:15:18]

Here we need to call SkScalarRoundToScalar(). The one thing this calculation
does backwards from the old way is that the old way calculates the scale from
the text size, but here we're getting the text size from the scale (which is
arguably the right way to think about it).

In the 'no hinting' case, this was already rounded to an integer (so that the
rest of the matrix is minimized), so there is no change there. In the 'hinted'
case, we've removed the entire scale from the matrix, so the scale value is the
'real' residual size. We used to round this size, and we should continue to do
so.

+    if (gdiTextSize == 0) {
+        gdiTextSize = SK_Scalar1;
+    }
 
     LOGFONT lf = typeface->fLogFont;
     lf.lfHeight = -SkScalarTruncToInt(gdiTextSize);