Re: math: ± and ∓ are shifted

[Hans Hagen <pragma@wxs.nl>]

On 4/5/2013 9:32 AM, Hans Hagen wrote:
> On 4/5/2013 2:16 AM, Khaled Hosny wrote:
>> On Fri, Apr 05, 2013 at 12:55:40AM +0200, Hans Hagen wrote:
>>> On 4/5/2013 12:13 AM, Aditya Mahajan wrote:
>>>> On Fri, 5 Apr 2013, Hans Hagen wrote:
>>>>
>>>>> On 4/4/2013 11:44 PM, Aditya Mahajan wrote:
>>>>>> On Thu, 4 Apr 2013, Xenia wrote:
>>>>>>
>>>>>>> Hi context list,
>>>>>>>
>>>>>>> I noticed that the ∓ sign is a little higher than the ± sign, so
>>>>>>> that
>>>>>>> the + signs are at the same height. But this looks strange and
>>>>>>> should be
>>>>>>> changed.
>>>>>>
>>>>>> Indeed. These look very odd. I tested this with cambria and the
>>>>>> outcome
>>>>>> is similar, so this is not a font bug, but something wrong in
>>>>>> ConTeXt's
>>>>>> math handling.
>>>>>
>>>>> I'm not sure if I understand the issue
>>>>>
>>>>> - lm has + and - touching with the + in the same position as the
>>>>> regular +
>>>>>
>>>>> - cambria has a gap between + and - and moves the + up and down
>>>>>
>>>>> Afaik context isn't doing any magic here as these are precomposed
>>>>> glyphs that directly map.
>>>>>
>>>>> $a \ruledhbox{$+$} b \ruledhbox{$-$} c$
>>>>>
>>>>> $a \ruledhbox{$±$} b \ruledhbox{$∓$} c$
>>>>>
>>>>> they are 'binary' in math mode, just like + and -
>>>>
>>>> The question is not about the shape of the glyph, but their location.
>>>> But after looking at the output of latex for CM and Cambria, I am no
>>>> longer sure what the correct output should be. For Cambria, ConTeXt and
>>>> LaTeX give similar outputs. For CM/LM they give different outputs.
>>>
>>> it looks like the open type version has a fitting boundingbox while
>>> the type 1 variants have a bit of the + sticking out:
>>
>> CFF fonts do not store bounding box info anywhere, the engine just
>> calculates it based on glyph outlines. For TFM fonts the metrics can be
>> adjusted to achieve specific alignment.
>
> Sure, but one can 'cheat' with the boundingboxes as they're not cropboxes.
>
> It's no big deal to adapt some metrics in mkiv, but best have the font
> do the job.

Experimental in beta:

\definefontfeature [lm-math] [mathdimensions=signs]

\starttext

\startTEXpage[offset=10pt]
     $x \ruledhbox{$\pm$} x \ruledhbox{$\mp$} x$
\stopTEXpage

\stoptext

(explanation in font manual, not yet uploaded)

Hans

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                                           Hans Hagen | PRAGMA ADE
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