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..216c7dce2c25dfbbcc4f88aaa83fd2c6444c71a3 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 +430,41 @@ 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);
+
+    // GetAlphaTextureBounds succeeds but returns an empty RECT if there are no
+    // glyphs of the specified texture type. When this happens, try with the
+    // alternate texture type.
+    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) {
+                glyph->fForceBW = 1;
+            }
+        }
+        // TODO: handle the case where a request for DWRITE_TEXTURE_ALIASED_1x1
+        // fails, and try DWRITE_TEXTURE_CLEARTYPE_3x1.
+    }
 
     glyph->fWidth = SkToU16(bbox.right - bbox.left);
     glyph->fHeight = SkToU16(bbox.bottom - bbox.top);
@@ -602,9 +627,12 @@ static void rgb_to_lcd32(const uint8_t* SK_RESTRICT src, const SkGlyph& glyph,
     }
 }
 
-const void* SkScalerContext_DW::drawDWMask(const SkGlyph& glyph) {
+const void* SkScalerContext_DW::drawDWMask(const SkGlyph& glyph,
+                                           DWRITE_RENDERING_MODE renderingMode,
+                                           DWRITE_TEXTURE_TYPE textureType)
+{
     int sizeNeeded = glyph.fWidth * glyph.fHeight;
-    if (DWRITE_RENDERING_MODE_ALIASED != fRenderingMode) {
+    if (DWRITE_RENDERING_MODE_ALIASED != renderingMode) {
         sizeNeeded *= 3;
     }
     if (sizeNeeded > fBits.count()) {
@@ -639,7 +667,7 @@ const void* SkScalerContext_DW::drawDWMask(const SkGlyph& glyph) {
     HRNM(fTypeface->fFactory->CreateGlyphRunAnalysis(&run,
                                           1.0f, // pixelsPerDip,
                                           &fXform,
-                                          fRenderingMode,
+                                          renderingMode,
                                           fMeasuringMode,
                                           0.0f, // baselineOriginX,
                                           0.0f, // baselineOriginY,
@@ -653,7 +681,7 @@ const void* SkScalerContext_DW::drawDWMask(const SkGlyph& glyph) {
     bbox.top = glyph.fTop;
     bbox.right = glyph.fLeft + glyph.fWidth;
     bbox.bottom = glyph.fTop + glyph.fHeight;
-    HRNM(glyphRunAnalysis->CreateAlphaTexture(fTextureType,
+    HRNM(glyphRunAnalysis->CreateAlphaTexture(textureType,
                                               &bbox,
                                               fBits.begin(),
                                               sizeNeeded),
@@ -663,7 +691,13 @@ const void* SkScalerContext_DW::drawDWMask(const SkGlyph& glyph) {
 
 void SkScalerContext_DW::generateImage(const SkGlyph& glyph) {
     //Create the mask.
-    const void* bits = this->drawDWMask(glyph);
+    DWRITE_RENDERING_MODE renderingMode = fRenderingMode;
+    DWRITE_TEXTURE_TYPE textureType = fTextureType;
+    if (glyph.fForceBW) {
+        renderingMode = DWRITE_RENDERING_MODE_ALIASED;
+        textureType = DWRITE_TEXTURE_ALIASED_1x1;
+    }
+    const void* bits = this->drawDWMask(glyph, renderingMode, textureType);
     if (!bits) {
         sk_bzero(glyph.fImage, glyph.computeImageSize());
         return;
@@ -671,7 +705,7 @@ void SkScalerContext_DW::generateImage(const SkGlyph& glyph) {
 
     //Copy the mask into the glyph.
     const uint8_t* src = (const uint8_t*)bits;
-    if (DWRITE_RENDERING_MODE_ALIASED == fRenderingMode) {
+    if (DWRITE_RENDERING_MODE_ALIASED == renderingMode) {
         bilevel_to_bw(src, glyph);
         const_cast<SkGlyph&>(glyph).fMaskFormat = SkMask::kBW_Format;
     } else if (!isLCD(fRec)) {