From d9a3309e8dc02fa9a2148e44ae7d866c558fbd3e Mon Sep 17 00:00:00 2001
From: Gary Qian <garyq@google.com>
Date: Wed, 17 Jul 2019 13:55:43 -0700
Subject: [PATCH] Fix justify for RTL paragraphs. (flutter/engine#9859)

---
 .../third_party/txt/src/txt/paragraph_txt.cc   | 13 +++++++++----
 .../third_party/txt/src/txt/paragraph_txt.h    |  4 +++-
 .../txt/tests/paragraph_unittests.cc           | 18 ++++++++++++++----
 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/engine/src/flutter/third_party/txt/src/txt/paragraph_txt.cc b/engine/src/flutter/third_party/txt/src/txt/paragraph_txt.cc
index 50fe8bb2109..5e62ea8dab9 100644
--- a/engine/src/flutter/third_party/txt/src/txt/paragraph_txt.cc
+++ b/engine/src/flutter/third_party/txt/src/txt/paragraph_txt.cc
@@ -1047,14 +1047,14 @@ void ParagraphTxt::Layout(double width) {
       // advance subtracted, so we do add the advance here to reset the
       // run_x_offset. We do keep the record though so GetRectsForRange() can
       // find metrics for trailing spaces.
-      // if (!run.is_ghost() || run.is_rtl()) {
       if ((!run.is_ghost() || run.is_rtl()) && !run.is_placeholder_run()) {
         run_x_offset += layout.getAdvance();
       }
     }  // for each in line_runs
 
     // Adjust the glyph positions based on the alignment of the line.
-    double line_x_offset = GetLineXOffset(run_x_offset);
+    double line_x_offset =
+        GetLineXOffset(run_x_offset, line_number, line_limit);
     if (line_x_offset) {
       for (CodeUnitRun& code_unit_run : line_code_unit_runs) {
         code_unit_run.Shift(line_x_offset);
@@ -1174,13 +1174,18 @@ void ParagraphTxt::Layout(double width) {
   longest_line_ = max_right_ - min_left_;
 }
 
-double ParagraphTxt::GetLineXOffset(double line_total_advance) {
+double ParagraphTxt::GetLineXOffset(double line_total_advance,
+                                    size_t line_number,
+                                    size_t line_limit) {
   if (isinf(width_))
     return 0;
 
   TextAlign align = paragraph_style_.effective_align();
 
-  if (align == TextAlign::right) {
+  if (align == TextAlign::right ||
+      (align == TextAlign::justify &&
+       paragraph_style_.text_direction == TextDirection::rtl &&
+       line_number == line_limit - 1)) {
     return width_ - line_total_advance;
   } else if (align == TextAlign::center) {
     return (width_ - line_total_advance) / 2;
diff --git a/engine/src/flutter/third_party/txt/src/txt/paragraph_txt.h b/engine/src/flutter/third_party/txt/src/txt/paragraph_txt.h
index b049902b55b..d1b68ab6f95 100644
--- a/engine/src/flutter/third_party/txt/src/txt/paragraph_txt.h
+++ b/engine/src/flutter/third_party/txt/src/txt/paragraph_txt.h
@@ -362,7 +362,9 @@ class ParagraphTxt : public Paragraph {
 
   // Calculate the starting X offset of a line based on the line's width and
   // alignment.
-  double GetLineXOffset(double line_total_advance);
+  double GetLineXOffset(double line_total_advance,
+                        size_t line_number,
+                        size_t line_limit);
 
   // Creates and draws the decorations onto the canvas.
   void PaintDecorations(SkCanvas* canvas,
diff --git a/engine/src/flutter/third_party/txt/tests/paragraph_unittests.cc b/engine/src/flutter/third_party/txt/tests/paragraph_unittests.cc
index 69ad4e5f10d..06f636e620d 100644
--- a/engine/src/flutter/third_party/txt/tests/paragraph_unittests.cc
+++ b/engine/src/flutter/third_party/txt/tests/paragraph_unittests.cc
@@ -1856,15 +1856,25 @@ TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(JustifyRTL)) {
     GetCanvas()->drawRect(boxes[i].rect, paint);
   }
   ASSERT_EQ(boxes.size(), 5ull);
+
+  paint.setColor(SK_ColorBLUE);
+  boxes = paragraph->GetRectsForRange(240, 250, rect_height_style,
+                                      rect_width_style);
+  for (size_t i = 0; i < boxes.size(); ++i) {
+    GetCanvas()->drawRect(boxes[i].rect, paint);
+  }
+  ASSERT_EQ(boxes.size(), 1ull);
+  EXPECT_FLOAT_EQ(boxes[0].rect.left(), 588);
+  EXPECT_FLOAT_EQ(boxes[0].rect.top(), 130);
+  EXPECT_FLOAT_EQ(boxes[0].rect.right(), 640);
+  EXPECT_FLOAT_EQ(boxes[0].rect.bottom(), 156);
   ASSERT_TRUE(Snapshot());
 
-  // All lines except the last should be justified to the width of the
+  // All lines should be justified to the width of the
   // paragraph.
-  for (size_t i = 0; i < paragraph->glyph_lines_.size() - 1; ++i) {
+  for (size_t i = 0; i < paragraph->glyph_lines_.size(); ++i) {
     ASSERT_EQ(glyph_line_width(i), paragraph_width);
   }
-  ASSERT_NE(glyph_line_width(paragraph->glyph_lines_.size() - 1),
-            paragraph_width);
 }
 
 TEST_F(ParagraphTest, DecorationsParagraph) {