win dw: Fallback to aliased if ClearType 'succeeds' but returns empty

src/ports/SkScalerContext_win_dw.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTypes.h"
 #undef GetGlyphIndices
 
@@ skipping 381 matching lines @@
         fG_inv.mapVectors(vecs, SK_ARRAY_COUNT(vecs));
     } else {
         fSkXform.mapVectors(vecs, SK_ARRAY_COUNT(vecs));
     }
 
     glyph->fAdvanceX = SkScalarToFixed(vecs[0].fX);
     glyph->fAdvanceY = SkScalarToFixed(vecs[0].fY);
 }
 
 void SkScalerContext_DW::generateMetrics(SkGlyph* glyph) {
+try_again:
     glyph->fWidth = 0;
 
     this->generateAdvance(glyph);
 
     //Measure raster size.
     fXform.dx = SkFixedToFloat(glyph->getSubXFixed());
     fXform.dy = SkFixedToFloat(glyph->getSubYFixed());
 
     FLOAT advance = 0;
 
@@ skipping 21 matching lines @@
              fRenderingMode,
              fMeasuringMode,
              0.0f, // baselineOriginX,
              0.0f, // baselineOriginY,
              &glyphRunAnalysis),
          "Could not create glyph run analysis.");
 
     RECT bbox;
     HRVM(glyphRunAnalysis->GetAlphaTextureBounds(fTextureType, &bbox),
          "Could not get texture bounds.");
+    if (bbox.right == 0 && bbox.left == 0 && bbox.top == 0 && bbox.bottom == 0 &&
+            fTextureType == DWRITE_TEXTURE_CLEARTYPE_3x1) {
+        fTextureType = DWRITE_TEXTURE_ALIASED_1x1;
+        fRenderingMode = DWRITE_RENDERING_MODE_ALIASED;
+        goto try_again;
+    }
 
     glyph->fWidth = SkToU16(bbox.right - bbox.left);
     glyph->fHeight = SkToU16(bbox.bottom - bbox.top);
     glyph->fLeft = SkToS16(bbox.left);
     glyph->fTop = SkToS16(bbox.top);
 }
 
 void SkScalerContext_DW::generateFontMetrics(SkPaint::FontMetrics* metrics) {
     if (NULL == metrics) {
         return;
@@ skipping 259 matching lines @@
                                        NULL, //advances
                                        NULL, //offsets
                                        1, //num glyphs
                                        FALSE, //sideways
                                        FALSE, //rtl
                                        geometryToPath.get()),
          "Could not create glyph outline.");
 
     path->transform(fSkXform);
 }