Bug 308471: Implement NSTextInput -characterIndexForPoint. Credits to mstange for virtually all the work in this patch. r=masayuki

widget/cocoa/TextInputHandler.mm

@@ -3199,15 +3199,34 @@ IMEInputHandler::FirstRectForCharacterRange(NSRange& aRange,
 NSUInteger
 IMEInputHandler::CharacterIndexForPoint(NSPoint& aPoint)
 {
+  NS_OBJC_BEGIN_TRY_ABORT_BLOCK_RETURN;
+
   PR_LOG(gLog, PR_LOG_ALWAYS,
     ("%p IMEInputHandler::CharacterIndexForPoint, aPoint={ x=%f, y=%f }",
      this, aPoint.x, aPoint.y));
 
-  //nsRefPtr<IMEInputHandler> kungFuDeathGrip(this);
+  NSWindow* mainWindow = [NSApp mainWindow];
+  if (!mWidget || !mainWindow) {
+    return NSNotFound;
+  }
 
-  // To implement this, we'd have to grovel in text frames looking at text
-  // offsets.
-  return 0;
+  WidgetQueryContentEvent charAt(true, NS_QUERY_CHARACTER_AT_POINT, mWidget);
+  NSPoint ptInWindow = [mainWindow convertScreenToBase:aPoint];
+  NSPoint ptInView = [mView convertPoint:ptInWindow fromView:nil];
+  charAt.refPoint.x =
+    static_cast<int32_t>(ptInView.x) * mWidget->BackingScaleFactor();
+  charAt.refPoint.y =
+    static_cast<int32_t>(ptInView.y) * mWidget->BackingScaleFactor();
+  mWidget->DispatchWindowEvent(charAt);
+  if (!charAt.mSucceeded ||
+      charAt.mReply.mOffset == WidgetQueryContentEvent::NOT_FOUND ||
+      charAt.mReply.mOffset >= static_cast<uint32_t>(NSNotFound)) {
+    return NSNotFound;
+  }
+
+  return charAt.mReply.mOffset;
+
+  NS_OBJC_END_TRY_ABORT_BLOCK_RETURN(NSNotFound);
 }
 
 NSArray*