DirectWrite to use aliased if ClearType is empty.

src/ports/SkScalerContext_win_dw.cpp

Index: src/ports/SkScalerContext_win_dw.cpp
diff --git a/src/ports/SkScalerContext_win_dw.cpp b/src/ports/SkScalerContext_win_dw.cpp
index f27497be62ef7e40fdc88fede12c183624cbb227..46769dfb288a96d4385de5e9df5d4de2cf2538b7 100644
--- a/src/ports/SkScalerContext_win_dw.cpp
+++ b/src/ports/SkScalerContext_win_dw.cpp
@@ -398,11 +398,11 @@ void SkScalerContext_DW::generateAdvance(SkGlyph* glyph) {
     glyph->fAdvanceY = SkScalarToFixed(vecs[0].fY);
 }
 
-void SkScalerContext_DW::generateMetrics(SkGlyph* glyph) {
-    glyph->fWidth = 0;
-
-    this->generateAdvance(glyph);
-
+void SkScalerContext_DW::getBoundingBox(SkGlyph* glyph,
+                                        DWRITE_RENDERING_MODE renderingMode,
+                                        DWRITE_TEXTURE_TYPE textureType,
+                                        RECT* bbox)
+{
     //Measure raster size.
     fXform.dx = SkFixedToFloat(glyph->getSubXFixed());
     fXform.dy = SkFixedToFloat(glyph->getSubYFixed());
@@ -430,16 +430,37 @@ void SkScalerContext_DW::generateMetrics(SkGlyph* glyph) {
              &run,
              1.0f, // pixelsPerDip,
              &fXform,
-             fRenderingMode,
+             renderingMode,
              fMeasuringMode,
              0.0f, // baselineOriginX,
              0.0f, // baselineOriginY,
              &glyphRunAnalysis),
          "Could not create glyph run analysis.");
 
-    RECT bbox;
-    HRVM(glyphRunAnalysis->GetAlphaTextureBounds(fTextureType, &bbox),
+    HRVM(glyphRunAnalysis->GetAlphaTextureBounds(textureType, bbox),
          "Could not get texture bounds.");
+}
+
+void SkScalerContext_DW::generateMetrics(SkGlyph* glyph) {
+    glyph->fWidth = 0;
+
+    this->generateAdvance(glyph);
+
+    RECT bbox;
+    this->getBoundingBox(glyph, fRenderingMode, fTextureType, &bbox);
+
+    if (bbox.left == bbox.right || bbox.top == bbox.bottom) {
+        if (DWRITE_TEXTURE_CLEARTYPE_3x1 == fTextureType) {
+            this->getBoundingBox(glyph,
+                                 DWRITE_RENDERING_MODE_ALIASED,
+                                 DWRITE_TEXTURE_ALIASED_1x1,
+                                 &bbox);
+            if (bbox.left != bbox.right && bbox.top != bbox.bottom) {

[reed1, 2014/08/27 22:07:33]

I'd add a comment inside the if...

// We concede that, from here out for this strike, we are force ourselves to
return BW glyphs.
// If it turns out that DW version alone is sufficient to know that LCD requests
will fail, we could
//    move the test into our constructor.
// If instead, we discover that this failure is not global per strike, then
overwriting fTextureType
//    here is overkill, and we should find a way to do this per-glyph (perhaps
checking for failure
//    in generateImage).

+                fTextureType = DWRITE_TEXTURE_ALIASED_1x1;
+                fRenderingMode = DWRITE_RENDERING_MODE_ALIASED;
+            }
+        }
+    }
 
     glyph->fWidth = SkToU16(bbox.right - bbox.left);
     glyph->fHeight = SkToU16(bbox.bottom - bbox.top);