libtxt: add a BoxHeightStyle option based on the height of the strut

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

@@ -1089,6 +1089,14 @@ enum BoxHeightStyle {
   ///
   /// {@macro flutter.dart:ui.boxHeightStyle.includeLineSpacing}
   includeLineSpacingBottom,
+
+  /// Calculate box heights based on the metrics of this paragraph's [StrutStyle].
+  ///
+  /// Boxes based on the strut will have consistent heights throughout the
+  /// 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.
+  strut,
 }
 
 /// Defines various ways to horizontally bound the boxes returned by

lib/ui/text.dart

@@ -1270,6 +1270,14 @@ enum BoxHeightStyle {
     ///
     /// {@macro flutter.dart:ui.boxHeightStyle.includeLineSpacing}
     includeLineSpacingBottom,
+
+    /// Calculate box heights based on the metrics of this paragraph's [StrutStyle].
+    ///
+    /// Boxes based on the strut will have consistent heights throughout the
+    /// 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.
+    strut,
 }
 
 /// Defines various ways to horizontally bound the boxes returned by

third_party/txt/src/txt/paragraph.cc

@@ -517,8 +517,7 @@ void Paragraph::Layout(double width, bool force) {
   double max_word_width = 0;
 
   // Compute strut minimums according to paragraph_style_.
-  StrutMetrics strut;
-  ComputeStrut(&strut, font);
+  ComputeStrut(&strut_, font);
 
   // Paragraph bounds tracking.
   size_t line_limit = std::min(paragraph_style_.max_lines, line_ranges_.size());
@@ -876,12 +875,12 @@ void Paragraph::Layout(double width, bool force) {
 
     // Calculate the amount to advance in the y direction. This is done by
     // computing the maximum ascent and descent with respect to the strut.
-    double max_ascent = strut.ascent + strut.half_leading;
-    double max_descent = strut.descent + strut.half_leading;
+    double max_ascent = strut_.ascent + strut_.half_leading;
+    double max_descent = strut_.descent + strut_.half_leading;
     SkScalar max_unscaled_ascent = 0;
     auto update_line_metrics = [&](const SkFontMetrics& metrics,
                                    const TextStyle& style) {
-      if (!strut.force_strut) {
+      if (!strut_.force_strut) {
         double ascent =
             (-metrics.fAscent + metrics.fLeading / 2) * style.height;
         max_ascent = std::max(ascent, max_ascent);
@@ -1442,7 +1441,8 @@ std::vector<Paragraph::TextBox> Paragraph::GetRectsForRange(
                 line_baselines_[kv.first] + line_max_descent_[kv.first]),
             box.direction);
       }
-    } else {  // kIncludeLineSpacingBottom
+    } else if (rect_height_style ==
+               RectHeightStyle::kIncludeLineSpacingBottom) {
       for (const Paragraph::TextBox& box : kv.second.boxes) {
         SkScalar adjusted_bottom =
             line_baselines_[kv.first] + line_max_descent_[kv.first];
@@ -1456,6 +1456,14 @@ std::vector<Paragraph::TextBox> Paragraph::GetRectsForRange(
                                             box.rect.fRight, adjusted_bottom),
                            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);
+      }
     }
   }
   return boxes;

third_party/txt/src/txt/paragraph.h

@@ -79,7 +79,10 @@ class Paragraph {
     // The line spacing will be added to the top of the rect.
     kIncludeLineSpacingTop,
     // The line spacing will be added to the bottom of the rect.
-    kIncludeLineSpacingBottom
+    kIncludeLineSpacingBottom,
+
+    // Calculate boxes based on the strut's metrics.
+    kStrut
   };
 
   enum class RectWidthStyle {
@@ -267,6 +270,18 @@ class Paragraph {
   std::vector<double> line_baselines_;
   bool did_exceed_max_lines_;
 
+  // Strut metrics of zero will have no effect on the layout.
+  struct StrutMetrics {
+    double ascent = 0;  // Positive value to keep signs clear.
+    double descent = 0;
+    double leading = 0;
+    double half_leading = 0;
+    double line_height = 0;
+    bool force_strut = false;
+  };
+
+  StrutMetrics strut_;
+
   // Metrics for use in GetRectsForRange(...);
   // Per-line max metrics over all runs in a given line.
   std::vector<SkScalar> line_max_spacings_;
@@ -372,16 +387,6 @@ class Paragraph {
         : x_start(x_s), y_start(y_s), x_end(x_e), y_end(y_e) {}
   };
 
-  // Strut metrics of zero will have no effect on the layout.
-  struct StrutMetrics {
-    double ascent = 0;  // Positive value to keep signs clear.
-    double descent = 0;
-    double leading = 0;
-    double half_leading = 0;
-    double line_height = 0;
-    bool force_strut = false;
-  };
-
   // Passes in the text and Styled Runs. text_ and runs_ will later be passed
   // into breaker_ in InitBreaker(), which is called in Layout().
   void SetText(std::vector<uint16_t> text, StyledRuns runs);

third_party/txt/tests/paragraph_unittests.cc

@@ -2200,6 +2200,65 @@ TEST_F(ParagraphTest,
   ASSERT_TRUE(Snapshot());
 }
 
+TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(GetRectsForRangeStrut)) {
+  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 = true;
+  paragraph_style.strut_font_families.push_back("Roboto");
+  paragraph_style.strut_font_size = 14;
+  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;
+  text_style.color = SK_ColorBLACK;
+  builder.PushStyle(text_style);
+
+  builder.AddText(u16_text);
+
+  builder.Pop();
+
+  auto paragraph = builder.Build();
+  paragraph->Layout(550);
+
+  paragraph->Paint(GetCanvas(), 0, 0);
+
+  SkPaint paint;
+  paint.setStyle(SkPaint::kStroke_Style);
+  paint.setAntiAlias(true);
+  paint.setStrokeWidth(1);
+
+  std::vector<txt::Paragraph::TextBox> strut_boxes =
+      paragraph->GetRectsForRange(0, 10, Paragraph::RectHeightStyle::kStrut,
+                                  Paragraph::RectWidthStyle::kMax);
+  ASSERT_EQ(strut_boxes.size(), 1ull);
+  const SkRect& strut_rect = strut_boxes.front().rect;
+  paint.setColor(SK_ColorRED);
+  GetCanvas()->drawRect(strut_rect, paint);
+
+  std::vector<txt::Paragraph::TextBox> tight_boxes =
+      paragraph->GetRectsForRange(0, 10, Paragraph::RectHeightStyle::kTight,
+                                  Paragraph::RectWidthStyle::kMax);
+  ASSERT_EQ(tight_boxes.size(), 1ull);
+  const SkRect& tight_rect = tight_boxes.front().rect;
+  paint.setColor(SK_ColorGREEN);
+  GetCanvas()->drawRect(tight_rect, paint);
+
+  EXPECT_FLOAT_EQ(strut_rect.left(), 0);
+  EXPECT_FLOAT_EQ(strut_rect.top(), 10.611719);
+  EXPECT_FLOAT_EQ(strut_rect.right(), 118.60547);
+  EXPECT_FLOAT_EQ(strut_rect.bottom(), 27.017969);
+
+  ASSERT_TRUE(tight_rect.contains(strut_rect));
+
+  ASSERT_TRUE(Snapshot());
+}
+
 SkRect GetCoordinatesForGlyphPosition(const txt::Paragraph& paragraph,
                                       size_t pos) {
   std::vector<txt::Paragraph::TextBox> boxes =