From c8e3e7e9bdd21fa24dd540ff43a11891d40ffe01 Mon Sep 17 00:00:00 2001
From: chunhtai <47866232+chunhtai@users.noreply.github.com>
Date: Mon, 10 Oct 2022 15:45:31 -0700
Subject: [PATCH] Apply text affinity fix to html rendering
 (flutter/engine#36699)

---
 .../lib/src/engine/text/canvas_paragraph.dart      | 14 +++++++++++---
 .../web_ui/test/text/canvas_paragraph_test.dart    |  8 ++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/engine/src/flutter/lib/web_ui/lib/src/engine/text/canvas_paragraph.dart b/engine/src/flutter/lib/web_ui/lib/src/engine/text/canvas_paragraph.dart
index df3680ad0c..b0de4f8611 100644
--- a/engine/src/flutter/lib/web_ui/lib/src/engine/text/canvas_paragraph.dart
+++ b/engine/src/flutter/lib/web_ui/lib/src/engine/text/canvas_paragraph.dart
@@ -229,9 +229,17 @@ class CanvasParagraph implements ui.Paragraph {
   @override
   ui.TextRange getWordBoundary(ui.TextPosition position) {
     final String text = toPlainText();
-
-    final int start = WordBreaker.prevBreakIndex(text, position.offset + 1);
-    final int end = WordBreaker.nextBreakIndex(text, position.offset);
+    final int characterPosition;
+    switch (position.affinity) {
+      case ui.TextAffinity.upstream:
+        characterPosition = position.offset - 1;
+        break;
+      case ui.TextAffinity.downstream:
+        characterPosition = position.offset;
+        break;
+    }
+    final int start = WordBreaker.prevBreakIndex(text, characterPosition + 1);
+    final int end = WordBreaker.nextBreakIndex(text, characterPosition);
     return ui.TextRange(start: start, end: end);
   }
 
diff --git a/engine/src/flutter/lib/web_ui/test/text/canvas_paragraph_test.dart b/engine/src/flutter/lib/web_ui/test/text/canvas_paragraph_test.dart
index 9262f0b2d7..6a7caaaf01 100644
--- a/engine/src/flutter/lib/web_ui/test/text/canvas_paragraph_test.dart
+++ b/engine/src/flutter/lib/web_ui/test/text/canvas_paragraph_test.dart
@@ -767,6 +767,14 @@ Future<void> testMain() async {
     expect(paragraph.getWordBoundary(const ui.TextPosition(offset: 17)), endRange);
   });
 
+  test('$CanvasParagraph.getWordBoundary can handle text affinity', () {
+    final ui.Paragraph paragraph = plain(ahemStyle, 'Lorem ipsum dolor');
+
+    const ui.TextRange loremRange = ui.TextRange(start: 0, end: 5);
+    expect(paragraph.getWordBoundary(const ui.TextPosition(offset: 4)), loremRange);
+    expect(paragraph.getWordBoundary(const ui.TextPosition(offset: 5, affinity: ui.TextAffinity.upstream)), loremRange);
+  });
+
   test('$CanvasParagraph.longestLine', () {
     final ui.Paragraph paragraph = plain(ahemStyle, 'abcd\nabcde abc');
     paragraph.layout(const ui.ParagraphConstraints(width: 80.0));