libtxt: have GetRectsForRange(strut) fall back to tight bounds if layout isn't forcing use of the strut

lib/stub_ui/lib/src/ui/text.dart

@@ -1235,6 +1235,8 @@ enum BoxHeightStyle {
   /// entire paragraph.  The top edge of each line will align with the bottom
   /// edge of the previous line.  It is possible for glyphs to extend outside
   /// these boxes.
+  ///
+  /// Will fall back to tight bounds if the strut is disabled or invalid.
   strut,
 }
 

lib/ui/text.dart

@@ -1429,6 +1429,8 @@ enum BoxHeightStyle {
     /// entire paragraph.  The top edge of each line will align with the bottom
     /// edge of the previous line.  It is possible for glyphs to extend outside
     /// these boxes.
+    ///
+    /// Will fall back to tight bounds if the strut is disabled or invalid.
     strut,
 }
 

third_party/txt/src/txt/paragraph.cc

@@ -425,6 +425,12 @@ bool Paragraph::ComputeBidiRuns(std::vector<BidiRun>* result) {
   return true;
 }
 
+bool Paragraph::IsStrutValid() const {
+  // Font size must be positive.
+  return (paragraph_style_.strut_enabled &&
+          paragraph_style_.strut_font_size >= 0);
+}
+
 void Paragraph::ComputeStrut(StrutMetrics* strut, SkFont& font) {
   strut->ascent = 0;
   strut->descent = 0;
@@ -433,15 +439,12 @@ void Paragraph::ComputeStrut(StrutMetrics* strut, SkFont& font) {
   strut->line_height = 0;
   strut->force_strut = false;
 
-  // Font size must be positive.
-  bool valid_strut =
-      paragraph_style_.strut_enabled && paragraph_style_.strut_font_size >= 0;
-  if (!valid_strut) {
+  if (!IsStrutValid())
     return;
-  }
+
   // force_strut makes all lines have exactly the strut metrics, and ignores all
   // actual metrics. We only force the strut if the strut is non-zero and valid.
-  strut->force_strut = paragraph_style_.force_strut_height && valid_strut;
+  strut->force_strut = paragraph_style_.force_strut_height;
   minikin::FontStyle minikin_font_style(
       0, GetWeight(paragraph_style_.strut_font_weight),
       paragraph_style_.strut_font_style == FontStyle::italic);
@@ -1458,12 +1461,18 @@ std::vector<Paragraph::TextBox> Paragraph::GetRectsForRange(
                            box.direction);
       }
     } else if (rect_height_style == RectHeightStyle::kStrut) {
-      for (const Paragraph::TextBox& box : kv.second.boxes) {
-        boxes.emplace_back(
-            SkRect::MakeLTRB(
-                box.rect.fLeft, line_baselines_[kv.first] - strut_.ascent,
-                box.rect.fRight, line_baselines_[kv.first] + strut_.descent),
-            box.direction);
+      if (IsStrutValid()) {
+        for (const Paragraph::TextBox& box : kv.second.boxes) {
+          boxes.emplace_back(
+              SkRect::MakeLTRB(
+                  box.rect.fLeft, line_baselines_[kv.first] - strut_.ascent,
+                  box.rect.fRight, line_baselines_[kv.first] + strut_.descent),
+              box.direction);
+        }
+      } else {
+        // Fall back to tight bounds if the strut is invalid.
+        boxes.insert(boxes.end(), kv.second.boxes.begin(),
+                     kv.second.boxes.end());
       }
     }
   }

third_party/txt/src/txt/paragraph.h

@@ -405,6 +405,8 @@ class Paragraph {
   // Calculates and populates strut based on paragraph_style_ strut info.
   void ComputeStrut(StrutMetrics* strut, SkFont& font);
 
+  bool IsStrutValid() const;
+
   // Calculate the starting X offset of a line based on the line's width and
   // alignment.
   double GetLineXOffset(double line_total_advance);

third_party/txt/tests/paragraph_unittests.cc

@@ -2259,6 +2259,41 @@ TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(GetRectsForRangeStrut)) {
   ASSERT_TRUE(Snapshot());
 }
 
+TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(GetRectsForRangeStrutFallback)) {
+  const char* text = "Chinese 字典";
+
+  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.strut_enabled = false;
+  txt::ParagraphBuilder builder(paragraph_style, GetTestFontCollection());
+
+  txt::TextStyle text_style;
+  text_style.font_families.push_back("Noto Sans CJK JP");
+  text_style.font_size = 20;
+  builder.PushStyle(text_style);
+
+  builder.AddText(u16_text);
+
+  builder.Pop();
+
+  auto paragraph = builder.Build();
+  paragraph->Layout(550);
+
+  std::vector<txt::Paragraph::TextBox> strut_boxes =
+      paragraph->GetRectsForRange(0, 10, Paragraph::RectHeightStyle::kStrut,
+                                  Paragraph::RectWidthStyle::kMax);
+  std::vector<txt::Paragraph::TextBox> tight_boxes =
+      paragraph->GetRectsForRange(0, 10, Paragraph::RectHeightStyle::kTight,
+                                  Paragraph::RectWidthStyle::kMax);
+
+  ASSERT_EQ(strut_boxes.size(), 1ull);
+  ASSERT_EQ(tight_boxes.size(), 1ull);
+  ASSERT_EQ(strut_boxes.front().rect, tight_boxes.front().rect);
+}
+
 SkRect GetCoordinatesForGlyphPosition(const txt::Paragraph& paragraph,
                                       size_t pos) {
   std::vector<txt::Paragraph::TextBox> boxes =