284815 - Invisible entities introduce white space in MathML.

Status: RESOLVED FIXED

(Core :: MathML, defect)

Description

[Brian Keay]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0

The invisible entities, such as ⁡ (a function) and ⁢ or ⁢
are supposed to have no visible effect on MathML rendering, but are used to
provide information on the content. Until recently, they were invisible, but now
they in the Linux based browsers they introduce white space, which leaves
equations looking aesthetically unappealing. I find myself deleting them, which
is unfortunate. In the Windows based Mozilla and Firefox browsers they still are
invisible. The problem seems only to be with the Linux browsers.

More specifically, if you go to
http://www.mozilla.org/projects/mathml/demo/tester.html and paste in the
following MathML markup

<math xmlns="&mathml;">
<mi>a</mi>
<mo>&InvisibleTimes;</mo>
<mi>b</mi>
</math>

it should look the same as the markup without the &InvisibleTimes;

<math xmlns="&mathml;">
<mi>a</mi>
<mi>b</mi>
</math>

Indeed, the visual difference is negligible on a Windows browser, but on the
newer Linux browsers (Mozilla 1.7+ and Firefox 1.0) a rather large white space
is introduced, leaving the equations looking aesthetically unappealing. This
problem didn't exist before.

Reproducible: Always

Steps to Reproduce:
More specifically, if you go to
http://www.mozilla.org/projects/mathml/demo/tester.html and paste in the
following MathML markup

<math xmlns="&mathml;">
<mi>a</mi>
<mo>&InvisibleTimes;</mo>
<mi>b</mi>
</math>

it should look the same as the markup without the &InvisibleTimes;

<math xmlns="&mathml;">
<mi>a</mi>
<mi>b</mi>
</math>

Indeed, the visual difference is negligible on a Windows browser, but on the
newer Linux browsers (Mozilla 1.7+ and Firefox 1.0) a rather large white space
is introduced, leaving the equations rather aesthetically unappealing.
Actual Results:  
Indeed, the visual difference is negligible on a Windows browser, as it should
be, but on the newer Linux browsers (Mozilla 1.7+ and Firefox 1.0) a rather
large white space is introduced, leaving the equations rather ugly.

Expected Results:  
Invisible entities, such as &af; and &InvisibleTimes; should be invisible and
not introduce large white spaces.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Looks like this broke between 2003-06-11-08 and 2003-06-12-08 builds.

Possibly fallout from bug 207438?  Nothing else in that range looks relevant...

Comment 2

[Boris Zbarsky [:bzbarsky]]

Yep, backing out that change fixes the bug.

Which makes me somewhat suspect it's a bug in some font....

Comment 3

[Boris Zbarsky [:bzbarsky]]

It looks like we have some chars with zero ascent/descent but nonzero width, at
least...

Comment 4

[Simon Montagu :smontagu]

(In reply to comment #2)
> Yep, backing out that change fixes the bug.
> 
> Which makes me somewhat suspect it's a bug in some font....

Yes, I think this is INVALID and the font is to blame. Can you identify the font
and ban it?

Comment 5

[Simon Montagu :smontagu]

... or maybe this is a dupe of bug 205387?

Comment 6

[Boris Zbarsky [:bzbarsky]]

Possible.  This is really not my area of expertise...

Comment 7

[rbs]

Fixed (by special-casing in the MathML context) via bug 306543.