Snap GDI matrix when snapping height.

src/ports/SkFontHost_win.cpp

Index: src/ports/SkFontHost_win.cpp
===================================================================
--- a/src/ports/SkFontHost_win.cpp	(revision 11569)
+++ b/src/ports/SkFontHost_win.cpp	(working copy)
@@ -663,17 +663,25 @@
     SkMatrix GA(G);
     GA.preConcat(A);
 
-    // textSize is the actual device size we want (as opposed to the size the user requested).
+    // realTextSize is the actual device size we want (as opposed to the size the user requested).
+    // gdiTextSizde is the size we request from GDI.
     // If the scale is negative, this means the matrix will do the flip anyway.
-    SkScalar textSize = SkScalarAbs(SkScalarRoundToScalar(GA.get(SkMatrix::kMScaleY)));
-    if (textSize == 0) {
-        textSize = SK_Scalar1;
+    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);
-    SkScalar scale = SkScalarInvert(textSize);
     sA.preScale(scale, scale); //remove text size
 
     // GsA is the non-rotational part of A without the text height scale.
@@ -692,7 +700,7 @@
                   G.get(SkMatrix::kMPersp0), G.get(SkMatrix::kMPersp1), G.get(SkMatrix::kMPersp2));
 
     LOGFONT lf = typeface->fLogFont;
-    lf.lfHeight = -SkScalarTruncToInt(textSize);
+    lf.lfHeight = -SkScalarTruncToInt(gdiTextSize);
     lf.lfQuality = compute_quality(fRec);
     fFont = CreateFontIndirect(&lf);
     if (!fFont) {
@@ -742,7 +750,7 @@
             this->forceGenerateImageFromPath();
         }
 
-        // Create a hires font if we need linear metrics.
+        // Create a hires matrix if we need linear metrics.
         if (this->isSubpixel()) {
             OUTLINETEXTMETRIC otm;
             UINT success = GetOutlineTextMetrics(fDDC, sizeof(otm), &otm);
@@ -751,17 +759,17 @@
                 success = GetOutlineTextMetrics(fDDC, sizeof(otm), &otm);
             }
             if (0 != success) {
-                SkScalar scale = SkIntToScalar(otm.otmEMSquare);
+                SkScalar upem = SkIntToScalar(otm.otmEMSquare);
 
-                SkScalar textScale = scale / textSize;
-                fHighResMat22.eM11 = float2FIXED(textScale);
+                SkScalar gdiTextSizeToEMScale = upem / gdiTextSize;
+                fHighResMat22.eM11 = float2FIXED(gdiTextSizeToEMScale);
                 fHighResMat22.eM12 = float2FIXED(0);
                 fHighResMat22.eM21 = float2FIXED(0);
-                fHighResMat22.eM22 = float2FIXED(textScale);
+                fHighResMat22.eM22 = float2FIXED(gdiTextSizeToEMScale);
 
-                SkScalar invScale = SkScalarInvert(scale);
+                SkScalar removeEMScale = SkScalarInvert(upem);
                 fHiResMatrix = A;
-                fHiResMatrix.preScale(invScale, invScale);
+                fHiResMatrix.preScale(removeEMScale, removeEMScale);
             }
         }