27874 - line-height should use em-square height, not bounding box height {ll}

Status: VERIFIED DUPLICATE of bug 27164

(Core :: Layout, defect, P3)

Description

[Hixie (not reading bugmail)]

Mozilla currently *sets* the font size in the correct way (i.e. em square), but 
the line height is based on GetHeight, which returns the bounding box height of
the font and not its em-square height.

We should change line-height to use the em-square height, and stop treating
   line-height: normal
...as 1.0. Instead, we should treat 'normal' as meaning 'the value recommended
by the font'.

Bug History: see bug 4234, bug 13072.
See also bug 27164: "update nsIFontMetrics API".

The test case to look at is:
   http://www.bath.ac.uk/%7Epy8ieh/internet/eviltests/lineheight7.html

Some other related test pages:
   http://www.fas.harvard.edu/~dbaron/css/fonts/sizes/
   http://www.fas.harvard.edu/~dbaron/css/test/inlinetest
   http://www.fas.harvard.edu/~dbaron/css/test/linebox4
   http://www.fas.harvard.edu/~dbaron/css/test/emunit
   http://www.bath.ac.uk/%7Epy8ieh/internet/eviltests/lineheight1.html
   http://www.bath.ac.uk/%7Epy8ieh/internet/eviltests/lineheight2.html
   http://www.bath.ac.uk/%7Epy8ieh/internet/eviltests/lineheight3.html
   http://www.bath.ac.uk/%7Epy8ieh/internet/eviltests/lineheight4.html

Comment 1

[Hixie (not reading bugmail)]

Setting milestone to M15 as per bug 27164, which this bug depends on.
See also bug 27873. Adding css1 keyword.

Comment 2

[Erik van der Poel]

I intend to fix this as part of fixing bug 20394.

Comment 3

[Erik van der Poel]

Targetting M16, since 20394 is also M16.

Comment 4

[Erik van der Poel]

Copied comments to bug 27164, marking this one a dup of 27164.

*** This bug has been marked as a duplicate of 27164 ***

Comment 5

[Chris Petersen]

Marking verified dup of 27164.