Snap GDI matrix when snapping height.

src/ports/SkFontHost_win.cpp

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkAdvancedTypefaceMetrics.h"
 #include "SkBase64.h"
@@ skipping 645 matching lines @@
     // G is the Given's Matrix for A (rotational matrix such that GA[0][1] == 0).
     SkMatrix G;
     G.setAll(c, -s, 0,
              s,  c, 0,
              0,  0, SkScalarToPersp(SK_Scalar1));
 
     // GA is the matrix A with rotation removed.
     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.
     // 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.
 
     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));
 
     LOGFONT lf = typeface->fLogFont;
-    lf.lfHeight = -SkScalarTruncToInt(textSize);
+    lf.lfHeight = -SkScalarTruncToInt(gdiTextSize);
     lf.lfQuality = compute_quality(fRec);
     fFont = CreateFontIndirect(&lf);
     if (!fFont) {
         return;
     }
 
     fSavefont = (HFONT)SelectObject(fDDC, fFont);
 
     if (0 == GetTextMetrics(fDDC, &fTM)) {
         call_ensure_accessible(lf);
@@ skipping 29 matching lines @@
         // MAT2 is row major, right handed (y up).
         fMat22.eM11 = float2FIXED(xform.eM11);
         fMat22.eM12 = float2FIXED(-xform.eM12);
         fMat22.eM21 = float2FIXED(-xform.eM21);
         fMat22.eM22 = float2FIXED(xform.eM22);
 
         if (needToRenderWithSkia(fRec)) {
             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);
             if (0 == success) {
                 call_ensure_accessible(lf);
                 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);
             }
         }
 
     } else {
         // Assume bitmap
         fType = SkScalerContext_GDI::kBitmap_Type;
 
         xform.eM11 = 1.0f;
         xform.eM12 = 0.0f;
         xform.eM21 = 0.0f;
@@ skipping 1632 matching lines @@
 
 SkTypeface* SkFontHost::CreateTypefaceFromStream(SkStream* stream) {
     return create_from_stream(stream);
 }
 
 #endif
 
 SkFontMgr* SkFontMgr_New_GDI() {
     return SkNEW(SkFontMgrGDI);
 }