[LayoutNG] Fix ShapingLineBreaker when the end of range is needed

third_party/WebKit/Source/platform/fonts/shaping/ShapingLineBreaker.cpp

Index: third_party/WebKit/Source/platform/fonts/shaping/ShapingLineBreaker.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/shaping/ShapingLineBreaker.cpp b/third_party/WebKit/Source/platform/fonts/shaping/ShapingLineBreaker.cpp
index dafe8f19e9a07cc0bdc11a84600fe359ea0e06c8..d306d49a9173dce81b968d9d818ae9ce47e75bd4 100644
--- a/third_party/WebKit/Source/platform/fonts/shaping/ShapingLineBreaker.cpp
+++ b/third_party/WebKit/Source/platform/fonts/shaping/ShapingLineBreaker.cpp
@@ -122,6 +122,15 @@ PassRefPtr<ShapeResult> ShapingLineBreaker::ShapeLine(
   DCHECK_GE(FlipRtl(end_position - start_position, direction), LayoutUnit(0));
   unsigned candidate_break =
       result_->OffsetForPosition(end_position, false) + range_start;
+
+  if (candidate_break >= range_end) {

[eae, 2017/06/12 16:51:37]

When would this happen?

[kojii, 2017/06/12 16:54:34]

"==" happens when end_position >= result->Width(). ">" should never happen, so I
have DCHECK below.

+    // The |result_| does not have glyphs to fill the available space,
+    // and thus unable to compute. Return the result up to range_end.
+    DCHECK_EQ(candidate_break, range_end);
+    *break_offset = range_end;
+    return ShapeToEnd(start, start_position, range_end);
+  }
+
   // candidate_break should be >= start, but rounding errors can chime in when
   // comparing floats. See ShapeLineZeroAvailableWidth on Linux/Mac.
   candidate_break = std::max(candidate_break, start);
@@ -130,6 +139,9 @@ PassRefPtr<ShapeResult> ShapingLineBreaker::ShapeLine(
   if (break_opportunity <= start) {
     break_opportunity = break_iterator_->NextBreakOpportunity(
         std::max(candidate_break, start + 1));
+    // |range_end| may not be a break opportunity, but this function cannot
+    // measure beyond it.
+    break_opportunity = std::min(break_opportunity, range_end);
   }
   DCHECK_GT(break_opportunity, start);
 
@@ -167,9 +179,9 @@ PassRefPtr<ShapeResult> ShapingLineBreaker::ShapeLine(
       LayoutUnit safe_position = SnapStart(
           result_->PositionForOffset(previous_safe - range_start), direction);
       while (break_opportunity > previous_safe && previous_safe >= start) {
+        DCHECK_LE(break_opportunity, range_end);
         line_end_result =
-            shaper_->Shape(font_, direction, previous_safe,
-                           std::min(break_opportunity, range_end));
+            shaper_->Shape(font_, direction, previous_safe, break_opportunity);
         if (line_end_result->SnappedWidth() <=
             FlipRtl(end_position - safe_position, direction))
           break;
@@ -193,6 +205,9 @@ PassRefPtr<ShapeResult> ShapingLineBreaker::ShapeLine(
     // No suitable break opportunity, not exceeding the available space,
     // found. Choose the next valid one even though it will overflow.
     break_opportunity = break_iterator_->NextBreakOpportunity(candidate_break);
+    // |range_end| may not be a break opportunity, but this function cannot
+    // measure beyond it.
+    break_opportunity = std::min(break_opportunity, range_end);
   }
 
   // Create shape results for the line by copying from the re-shaped result (if
@@ -214,4 +229,31 @@ PassRefPtr<ShapeResult> ShapingLineBreaker::ShapeLine(
   return line_result.Release();
 }
 
+// Shape from the specified offset to the end of the ShapeResult.
+// If |start| is safe-to-break, this copies the subset of the result.
+PassRefPtr<ShapeResult> ShapingLineBreaker::ShapeToEnd(
+    unsigned start,
+    LayoutUnit start_position,
+    unsigned range_end) {
+  unsigned first_safe =
+      NextSafeToBreakBefore(shaper_->GetText(), shaper_->TextLength(), start);
+  DCHECK_GE(first_safe, start);
+
+  RefPtr<ShapeResult> line_result;
+  TextDirection direction = result_->Direction();
+  if (first_safe == start) {
+    // If |start| is safe-to-break, reshape is not needed.
+    line_result = ShapeResult::Create(font_, 0, direction);
+    result_->CopyRange(start, range_end, line_result.Get());
+  } else if (first_safe < range_end) {
+    // Otherwise reshape to the first safe, then copy the rest.
+    line_result = shaper_->Shape(font_, direction, start, first_safe);
+    result_->CopyRange(first_safe, range_end, line_result.Get());
+  } else {
+    // If no safe-to-break in the ragne, reshape the whole range.
+    line_result = shaper_->Shape(font_, direction, start, range_end);
+  }
+  return line_result.Release();
+}
+
 }  // namespace blink