Fix cursor jumping when typing some special characters. (#7964)

third_party/txt/src/txt/paragraph.cc

@@ -1248,6 +1248,7 @@ std::vector<Paragraph::TextBox> Paragraph::GetRectsForRange(
   // Lines that are actually in the requested range.
   size_t max_line = 0;
   size_t min_line = INT_MAX;
+  size_t glyph_length = 0;
 
   // Generate initial boxes and calculate metrics.
   for (const CodeUnitRun& run : code_unit_runs_) {
@@ -1276,6 +1277,15 @@ std::vector<Paragraph::TextBox> Paragraph::GetRectsForRange(
         if (gp.code_units.start >= start && gp.code_units.end <= end) {
           left = std::min(left, static_cast<SkScalar>(gp.x_pos.start));
           right = std::max(right, static_cast<SkScalar>(gp.x_pos.end));
+        } else if (gp.code_units.end == end) {
+          // Calculate left and right when we are at
+          // the last position of a combining character.
+          glyph_length = (gp.code_units.end - gp.code_units.start) - 1;
+          if (gp.code_units.start ==
+              std::max<size_t>(0, (start - glyph_length))) {
+            left = std::min(left, static_cast<SkScalar>(gp.x_pos.start));
+            right = std::max(right, static_cast<SkScalar>(gp.x_pos.end));
+          }
         }
       }
       if (left == SK_ScalarMax || right == SK_ScalarMin)

third_party/txt/tests/paragraph_unittests.cc

@@ -1673,6 +1673,92 @@ TEST_F(ParagraphTest,
   ASSERT_TRUE(Snapshot());
 }
 
+TEST_F(ParagraphTest, GetRectsForRangeIncludeCombiningCharacter) {
+  const char* text = "ดีสวัสดีชาวโลกที่น่ารัก";
+  auto icu_text = icu::UnicodeString::fromUTF8(text);
+  std::u16string u16_text(icu_text.getBuffer(),
+                          icu_text.getBuffer() + icu_text.length());
+
+  txt::ParagraphStyle paragraph_style;
+  paragraph_style.max_lines = 10;
+  paragraph_style.text_align = TextAlign::left;
+  txt::ParagraphBuilder builder(paragraph_style, GetTestFontCollection());
+
+  txt::TextStyle text_style;
+  text_style.font_families = std::vector<std::string>(1, "Roboto");
+  text_style.font_size = 50;
+  text_style.letter_spacing = 1;
+  text_style.word_spacing = 5;
+  text_style.color = SK_ColorBLACK;
+  text_style.height = 1;
+  builder.PushStyle(text_style);
+
+  builder.AddText(u16_text);
+
+  builder.Pop();
+
+  auto paragraph = builder.Build();
+  paragraph->Layout(GetTestCanvasWidth() - 100);
+
+  paragraph->Paint(GetCanvas(), 0, 0);
+
+  Paragraph::RectHeightStyle rect_height_style =
+      Paragraph::RectHeightStyle::kTight;
+  Paragraph::RectWidthStyle rect_width_style =
+      Paragraph::RectWidthStyle::kTight;
+
+  std::vector<txt::Paragraph::TextBox> boxes =
+      paragraph->GetRectsForRange(0, 0, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 0ull);
+
+  // Case when the sentence starts with a combining character
+  // We should get 0 box for ด because it's already been combined to ดี
+  boxes =
+      paragraph->GetRectsForRange(0, 1, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 0ull);
+
+  boxes =
+      paragraph->GetRectsForRange(1, 2, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 1ull);
+
+  boxes =
+      paragraph->GetRectsForRange(0, 2, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 1ull);
+
+  // Case when the sentence contains a combining character
+  // We should get 0 box for ว because it's already been combined to วั
+  boxes =
+      paragraph->GetRectsForRange(3, 4, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 0ull);
+
+  boxes =
+      paragraph->GetRectsForRange(4, 5, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 1ull);
+
+  boxes =
+      paragraph->GetRectsForRange(3, 5, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 1ull);
+
+  // Case when the sentence contains a combining character that contain 3
+  // characters We should get 0 box for ท and ที because it's already been
+  // combined to ที่
+  boxes =
+      paragraph->GetRectsForRange(14, 15, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 0ull);
+
+  boxes =
+      paragraph->GetRectsForRange(15, 16, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 0ull);
+
+  boxes =
+      paragraph->GetRectsForRange(16, 17, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 1ull);
+
+  boxes =
+      paragraph->GetRectsForRange(14, 17, rect_height_style, rect_width_style);
+  EXPECT_EQ(boxes.size(), 1ull);
+}
+
 TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(GetRectsForRangeCenterParagraph)) {
   const char* text = "01234  　 ";  // includes ideographic space
                                     // and english space.