Use the font height as caret height instead of the line height

third_party/WebKit/Source/core/layout/LayoutText.cpp

 /*
  * (C) 1999 Lars Knoll (knoll@kde.org)
  * (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Andrew Wellington (proton@wiretapped.net)
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 715 matching lines @@
                                       LayoutUnit* extraWidthToEndOfLine) {
   if (!inlineBox)
     return LayoutRect();
 
   ASSERT(inlineBox->isInlineTextBox());
   if (!inlineBox->isInlineTextBox())
     return LayoutRect();
 
   InlineTextBox* box = toInlineTextBox(inlineBox);
 
-  int height = box->root().selectionHeight().toInt();
-  int top = box->root().selectionTop().toInt();
+  int height = style()->font().primaryFont()->getFontMetrics().height();

[yosin_UTC9, 2016/11/30 01:44:02]

Could you use font ascendant and descendant instead of height?

top = baseline - font_ascendant;
bottom = baseline + font_descendant;

BTW, I'm not sure we should use actual font instead of computed font.
The font used by |inlineBox| can be different of |style()->font()| due by
missing glyph, e.g. kanji character with "font-family: Arial".

I found following code fragment in InlineTextBoxPainter:

  const ComputedStyle& styleToUse =
      m_inlineTextBox.getLineLayoutItem().styleRef(
          m_inlineTextBox.isFirstLineStyle());

Note: ::first-letter characters and rest of characters are placed into different
InlineTextBox.

I'm not an expert of this area, drott@ will provide more information.

[joone, 2016/12/02 01:24:43]

But, we need the height value and can get it easily by just calling the height
method of FontMetrics: the height value is calculated by ascent() + descent().
I used the above code to get the computed font.

[yosin_UTC9, 2016/12/02 01:42:35]

This function returns rectangle rather than height. Caret rectangle should be:

line top

  +
  |
  |
  |
 -+- baseline
  |

line bottom


This patch returns:


line top

  +
  |
  |
  |
  |
  +- line bottom

+  int top = box->root().selectionBottom().toInt() - height;
 
   // Go ahead and round left to snap it to the nearest pixel.
   LayoutUnit left = box->positionForOffset(caretOffset);
 
   // Distribute the caret's width to either side of the offset.
   LayoutUnit caretWidthLeftOfOffset = caretWidth() / 2;
   left -= caretWidthLeftOfOffset;
   LayoutUnit caretWidthRightOfOffset = caretWidth() - caretWidthLeftOfOffset;
 
   left = LayoutUnit(left.round());
@@ skipping 1227 matching lines @@
   LayoutRect rect = LayoutRect(
       IntRect(firstRunX(), firstRunY(), linesBox.width(), linesBox.height()));
   LayoutBlock* block = containingBlock();
   if (block && hasTextBoxes())
     block->adjustChildDebugRect(rect);
 
   return rect;
 }
 
 }  // namespace blink