[TextBlob] Fall back to TightRunBounds when the font bounds are empty

src/core/SkTextBlob.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTextBlob.h"
 
 #include "SkReadBuffer.h"
@@ skipping 364 matching lines @@
     paint.measureText(run.glyphBuffer(), run.glyphCount() * sizeof(uint16_t), &bounds);
 
     return bounds.makeOffset(run.offset().x(), run.offset().y());
 }
 
 SkRect SkTextBlobBuilder::ConservativeRunBounds(const SkTextBlob::RunRecord& run) {
     SkASSERT(run.glyphCount() > 0);
     SkASSERT(SkTextBlob::kFull_Positioning == run.positioning() ||
              SkTextBlob::kHorizontal_Positioning == run.positioning());
 
-    // First, compute the glyph position bbox.
+    SkPaint paint;
+    run.font().applyToPaint(&paint);
+    const SkRect fontBounds = paint.getFontBounds();
+    if (fontBounds.isEmpty()) {
+        // Empty font bounds are likely a font bug.  TightBounds has a better chance of
+        // producing useful results in this case.
+        return TightRunBounds(run);
+    }
+
+    // Compute the glyph position bbox.
     SkRect bounds;
     switch (run.positioning()) {
     case SkTextBlob::kHorizontal_Positioning: {
         const SkScalar* glyphPos = run.posBuffer();
         SkASSERT((void*)(glyphPos + run.glyphCount()) <= SkTextBlob::RunRecord::Next(&run));
 
         SkScalar minX = *glyphPos;
         SkScalar maxX = *glyphPos;
         for (unsigned i = 1; i < run.glyphCount(); ++i) {
             SkScalar x = glyphPos[i];
             minX = SkMinScalar(x, minX);
             maxX = SkMaxScalar(x, maxX);
         }
 
         bounds.setLTRB(minX, 0, maxX, 0);
     } break;
     case SkTextBlob::kFull_Positioning: {
         const SkPoint* glyphPosPts = reinterpret_cast<const SkPoint*>(run.posBuffer());
         SkASSERT((void*)(glyphPosPts + run.glyphCount()) <= SkTextBlob::RunRecord::Next(&run));
 
         bounds.setBounds(glyphPosPts, run.glyphCount());
     } break;
     default:
         SkFAIL("unsupported positioning mode");
     }
 
     // Expand by typeface glyph bounds.
-    SkPaint paint;
-    run.font().applyToPaint(&paint);
-    const SkRect fontBounds = paint.getFontBounds();
     bounds.fLeft   += fontBounds.left();
     bounds.fTop    += fontBounds.top();
     bounds.fRight  += fontBounds.right();
     bounds.fBottom += fontBounds.bottom();
 
     // Offset by run position.
     return bounds.makeOffset(run.offset().x(), run.offset().y());
 }
 
 void SkTextBlobBuilder::updateDeferredBounds() {
@@ skipping 174 matching lines @@
 
     fStorageUsed = 0;
     fStorageSize = 0;
     fRunCount = 0;
     fLastRun = 0;
     fBounds.setEmpty();
 
     return blob;
 }