[LayoutNG] Implement glyph bounding box to ShapeResult::CopyRange()

For LayoutNG inline to compute visual overflow, ShapingLineBreaker needs
to compute glyph bounding box. This is currently set to empty.

To implement:
1. ShapeResult::CopyRange() should copy adjusted glyph bounding box
   when copying start/end edge of the source.
2. When start/end is safe-to-break, ShapingLineBreaker subsets
   ShapeResult, but unable to compute glyph bounding box.

This patch implements #1. How to solve #2 is to be discussed.

BUG=636993
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_layout_ng

Change-Id: Ic239c8531bb2e5f09e2e80d7ea7e0e25c6aaa847
Reviewed-on: https://chromium-review.googlesource.com/574508
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487410}

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

@@ -407,6 +407,7 @@ TEST_F(HarfBuzzShaperTest, ShapeResultCopyRangeIntoLatin) {
 
   EXPECT_EQ(result->NumCharacters(), composite_result->NumCharacters());
   EXPECT_EQ(result->SnappedWidth(), composite_result->SnappedWidth());
+  EXPECT_EQ(result->Bounds(), composite_result->Bounds());
   EXPECT_EQ(result->SnappedStartPositionForOffset(0),
             composite_result->SnappedStartPositionForOffset(0));
   EXPECT_EQ(result->SnappedStartPositionForOffset(15),
@@ -432,6 +433,7 @@ TEST_F(HarfBuzzShaperTest, ShapeResultCopyRangeIntoArabicThaiHanLatin) {
 
   EXPECT_EQ(result->NumCharacters(), composite_result->NumCharacters());
   EXPECT_EQ(result->SnappedWidth(), composite_result->SnappedWidth());
+  EXPECT_EQ(result->Bounds(), composite_result->Bounds());
   EXPECT_EQ(result->SnappedStartPositionForOffset(0),
             composite_result->SnappedStartPositionForOffset(0));
   EXPECT_EQ(result->SnappedStartPositionForOffset(1),
@@ -468,4 +470,22 @@ TEST_F(HarfBuzzShaperTest, ShapeResultCopyRangeAcrossRuns) {
   EXPECT_EQ(2u, target->NumCharacters());
 }
 
+TEST_F(HarfBuzzShaperTest, ShapeResultCopyRangeSegmentGlyphBoundingBox) {
+  String string(u"THello worldL");
+  TextDirection direction = TextDirection::kLtr;
+
+  HarfBuzzShaper shaper(string.Characters16(), string.length());
+  RefPtr<ShapeResult> result1 = shaper.Shape(&font, direction, 0, 6);
+  RefPtr<ShapeResult> result2 =
+      shaper.Shape(&font, direction, 6, string.length());
+
+  RefPtr<ShapeResult> composite_result =
+      ShapeResult::Create(&font, 0, direction);
+  result1->CopyRange(0, 6, composite_result.Get());
+  result2->CopyRange(6, string.length(), composite_result.Get());
+
+  RefPtr<ShapeResult> result = shaper.Shape(&font, direction);
+  EXPECT_EQ(result->Bounds(), composite_result->Bounds());
+}
+
 }  // namespace blink

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

@@ -456,6 +456,7 @@ void ShapeResult::CopyRange(unsigned start_offset,
                             unsigned end_offset,
                             ShapeResult* target) const {
   unsigned index = target->num_characters_;
+  float total_width = 0;
   for (const auto& run : runs_) {
     unsigned run_start = (*run).start_index_;
     unsigned run_end = run_start + (*run).num_characters_;
@@ -467,12 +468,37 @@ void ShapeResult::CopyRange(unsigned start_offset,
 
       auto sub_run = (*run).CreateSubRun(start, end);
       sub_run->start_index_ = index;
-      target->width_ += sub_run->width_;
+      total_width += sub_run->width_;
       index += sub_run->num_characters_;
       target->runs_.push_back(std::move(sub_run));
     }
   }
 
+  // Compute new glyph bounding box.
+  // If |start_offset| or |end_offset| are the start/end of |this|, use
+  // |glyph_bounding_box_| from |this| for the side. Otherwise, we cannot
+  // compute accurate glyph bounding box; approximate by assuming there are no
+  // glyph overflow nor underflow.
+  // TODO(kojii): This is not correct for vertical flow since glyphs are in
+  // physical coordinates.
+  float left = target->width_;
+  target->width_ += total_width;
+  float right = target->width_;
+  if (start_offset <= StartIndexForResult())
+    left += glyph_bounding_box_.X();
+  if (end_offset >= EndIndexForResult())
+    right += glyph_bounding_box_.MaxX() - width_;
+  if (right >= left) {
+    FloatRect adjusted_box(left, glyph_bounding_box_.Y(), right - left,
+                           glyph_bounding_box_.Height());
+    target->glyph_bounding_box_.UniteIfNonZero(adjusted_box);
+  } else {
+    FloatRect adjusted_box(left, glyph_bounding_box_.Y(), 0,
+                           glyph_bounding_box_.Height());
+    target->glyph_bounding_box_.UniteIfNonZero(adjusted_box);
+    target->glyph_bounding_box_.ShiftMaxXEdgeTo(right);
+  }
+
   DCHECK_EQ(index - target->num_characters_,
             std::min(end_offset, EndIndexForResult()) -
                 std::max(start_offset, StartIndexForResult()));