Restore GDI text size rounding.

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 598 matching lines @@
 {
     LogFontTypeface* typeface = reinterpret_cast<LogFontTypeface*>(rawTypeface);
 
     fDDC = ::CreateCompatibleDC(NULL);
     if (!fDDC) {
         return;
     }
     SetGraphicsMode(fDDC, GM_ADVANCED);
     SetBkMode(fDDC, TRANSPARENT);
 
-    // When GDI hinting, remove the entire Y scale to prevent 'subpixel' metrics.
-    // When not hinting, remove only the gdiTextSize scale which will be applied by GDI.
+    // When GDI hinting, remove the entire Y scale from sA and GsA. (Prevents 'linear' metrics.)
+    // When not hinting, remove only the integer Y scale from sA and GsA. (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));
 
-    SkScalar gdiTextSize = scale.fY;
+    // When not hinting, scale was computed with kVerticalInteger, so is already an integer.
+    // The sA and GsA transforms will be used to create 'linear' metrics.
+
+    // When hinting, scale was computed with kVertical, stating that our port can handle
+    // non-integer scales. This is done so that sA and GsA are computed without any 'residual'
+    // scale in them, preventing 'linear' metrics. However, GDI cannot actually handle non-integer
+    // scales so we need to round in this case. This is fine, since all of the scale has been
+    // removed from sA and GsA, so GDI will be handling the scale completely.
+    SkScalar gdiTextSize = SkScalarRoundToScalar(scale.fY);
+
+    // GDI will not accept a size of zero, so round the range [0, 1] to 1.
+    // If the size was non-zero, the scale factors will also be non-zero and 1px tall text is drawn.
+    // If the size actually was zero, the scale factors will also be zero, so GDI will draw nothing.
     if (gdiTextSize == 0) {
         gdiTextSize = SK_Scalar1;
     }
 
     LOGFONT lf = typeface->fLogFont;
     lf.lfHeight = -SkScalarTruncToInt(gdiTextSize);
     lf.lfQuality = compute_quality(fRec);
     fFont = CreateFontIndirect(&lf);
     if (!fFont) {
         return;
@@ skipping 1865 matching lines @@
 
 private:
     SkTDArray<ENUMLOGFONTEX> fLogFontArray;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
 SkFontMgr* SkFontMgr_New_GDI() {
     return SkNEW(SkFontMgrGDI);
 }