Fix error handling in DirectWrite with tiny text.

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 216c7dce2c25dfbbcc4f88aaa83fd2c6444c71a3..ae264563c7bf6ce1b7cf6111da38aed62f7bfb99 100644
--- a/src/ports/SkScalerContext_win_dw.cpp
+++ b/src/ports/SkScalerContext_win_dw.cpp
@@ -398,10 +398,10 @@ void SkScalerContext_DW::generateAdvance(SkGlyph* glyph) {
     glyph->fAdvanceY = SkScalarToFixed(vecs[0].fY);
 }
 
-void SkScalerContext_DW::getBoundingBox(SkGlyph* glyph,
-                                        DWRITE_RENDERING_MODE renderingMode,
-                                        DWRITE_TEXTURE_TYPE textureType,
-                                        RECT* bbox)
+HRESULT SkScalerContext_DW::getBoundingBox(SkGlyph* glyph,
+                                           DWRITE_RENDERING_MODE renderingMode,
+                                           DWRITE_TEXTURE_TYPE textureType,
+                                           RECT* bbox)
 {
     //Measure raster size.
     fXform.dx = SkFixedToFloat(glyph->getSubXFixed());
@@ -426,19 +426,21 @@ void SkScalerContext_DW::getBoundingBox(SkGlyph* glyph,
     run.glyphOffsets = &offset;
 
     SkTScopedComPtr<IDWriteGlyphRunAnalysis> glyphRunAnalysis;
-    HRVM(fTypeface->fFactory->CreateGlyphRunAnalysis(
-             &run,
-             1.0f, // pixelsPerDip,
-             &fXform,
-             renderingMode,
-             fMeasuringMode,
-             0.0f, // baselineOriginX,
-             0.0f, // baselineOriginY,
-             &glyphRunAnalysis),
-         "Could not create glyph run analysis.");
-
-    HRVM(glyphRunAnalysis->GetAlphaTextureBounds(textureType, bbox),
-         "Could not get texture bounds.");
+    HRM(fTypeface->fFactory->CreateGlyphRunAnalysis(
+            &run,
+            1.0f, // pixelsPerDip,
+            &fXform,
+            renderingMode,
+            fMeasuringMode,
+            0.0f, // baselineOriginX,
+            0.0f, // baselineOriginY,
+            &glyphRunAnalysis),
+        "Could not create glyph run analysis.");
+
+    HRM(glyphRunAnalysis->GetAlphaTextureBounds(textureType, bbox),
+        "Could not get texture bounds.");
+
+    return S_OK;
 }
 
 void SkScalerContext_DW::generateMetrics(SkGlyph* glyph) {
@@ -447,17 +449,19 @@ void SkScalerContext_DW::generateMetrics(SkGlyph* glyph) {
     this->generateAdvance(glyph);
 
     RECT bbox;
-    this->getBoundingBox(glyph, fRenderingMode, fTextureType, &bbox);
+    HRVM(this->getBoundingBox(glyph, fRenderingMode, fTextureType, &bbox),
+         "Requested bounding box could not be determined.");
 
     // 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);
+            HRVM(this->getBoundingBox(glyph,
+                                      DWRITE_RENDERING_MODE_ALIASED,
+                                      DWRITE_TEXTURE_ALIASED_1x1,
+                                      &bbox),
+                 "Fallback bounding box could not be determined.");
             if (bbox.left != bbox.right && bbox.top != bbox.bottom) {
                 glyph->fForceBW = 1;
             }
@@ -466,10 +470,21 @@ void SkScalerContext_DW::generateMetrics(SkGlyph* glyph) {
         // fails, and try DWRITE_TEXTURE_CLEARTYPE_3x1.
     }
 
-    glyph->fWidth = SkToU16(bbox.right - bbox.left);
-    glyph->fHeight = SkToU16(bbox.bottom - bbox.top);
-    glyph->fLeft = SkToS16(bbox.left);
-    glyph->fTop = SkToS16(bbox.top);
+    // GetAlphaTextureBounds succeeds but return bounds like
+    // { 0x80000000, 0x80000000, 0x80000000, 0x80000000 }
+    // for small, but not quite zero, sized glyphs.
+    // Normalize all empty rects to 0, 0, 0, 0.
+    if (bbox.left == bbox.right || bbox.top == bbox.bottom) {

[mtklein, 2014/08/28 17:25:49]

== -> >= for both, and above?

[bungeman-skia, 2014/08/28 18:01:04]

Done.

+        glyph->fWidth = 0;
+        glyph->fHeight = 0;
+        glyph->fLeft = 0;
+        glyph->fTop = 0;
+    } else {
+        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) {