issues with optical bounds

issues with optical bounds

[Pablo Rodriguez]

Hi Hans,

many thanks for having released the new beta.

I experience opposite results with opbd. The first sample is:

    \definefontfeature[default][default][protrusion=quality, opbd=yes]
    \definefontfamily[mainface][rm][Linux Libertine O]
    \setupbodyfont[mainface, 300pt]
    \setuppagenumbering[location=]
    \setupalign[hanging]
    \showframe
    \starttext
        W
    \stoptext

Although the value for that lfbd is only -29, the W is moved too much
from its original position.

The second sample is (font attached at
https://mailman.ntg.nl/pipermail/ntg-context/2018/092527.html):

    \showframe
    \definefontfeature[default][default][protrusion=quality, opbd=yes]
    \definefontfamily[mainface][rm][TestOPBD]
    \setupbodyfont[mainface, 60pt]
    \setupalign[hanging]

    \starttext
    Ἠ\\
    Ἠ\hfill Ἠ\\
    Ἦ\hfill ὩὩ\\
    ἯἯ\hfill ὩὩ
    \stoptext

Here the changes are tiny. The right values are used in the image at
https://github.com/wspr/fontspec/issues/282#issuecomment-287155442.

Could you check it?

Many thanks for your help,

Pablo
-- 
http://www.ousia.tk
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Re: issues with optical bounds

[Hans Hagen]

On 11/18/2018 10:22 PM, Pablo Rodriguez wrote:
> Hi Hans,
> 
> many thanks for having released the new beta.
> 
> I experience opposite results with opbd. The first sample is:
> 
>      \definefontfeature[default][default][protrusion=quality, opbd=yes]
>      \definefontfamily[mainface][rm][Linux Libertine O]
>      \setupbodyfont[mainface, 300pt]
>      \setuppagenumbering[location=]
>      \setupalign[hanging]
>      \showframe
>      \starttext
>          W
>      \stoptext
> 
> Although the value for that lfbd is only -29, the W is moved too much
> from its original position.

i have no time now but keep in mind that we also have a multiplier (the 
system is set up to use ratios / fractions, not hard coded numbers

also, it makes no sense to experiment too much with only some demo fonts 
with incomplete coverage ... adapting the low level mechanism to just 
one font with one character protruding makes no sense (one can tnen 
better use the non-opbd way)

> The second sample is (font attached at
> https://mailman.ntg.nl/pipermail/ntg-context/2018/092527.html):
> 
>      \showframe
>      \definefontfeature[default][default][protrusion=quality, opbd=yes]
>      \definefontfamily[mainface][rm][TestOPBD]
>      \setupbodyfont[mainface, 60pt]
>      \setupalign[hanging]
> 
>      \starttext
>      Ἠ\\
>      Ἠ\hfill Ἠ\\
>      Ἦ\hfill ὩὩ\\
>      ἯἯ\hfill ὩὩ
>      \stoptext
> 
> Here the changes are tiny. The right values are used in the image at
> https://github.com/wspr/fontspec/issues/282#issuecomment-287155442.
> 
> Could you check it?
> 
> Many thanks for your help,
> 
> Pablo
> 


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Re: issues with optical bounds

[Pablo Rodriguez]

On 11/18/18 10:37 PM, Hans Hagen wrote:
> On 11/18/2018 10:22 PM, Pablo Rodriguez wrote:
>> [...]
>>      \starttext
>>          W
>>      \stoptext
>>
>> Although the value for that lfbd is only -29, the W is moved too much
>> from its original position.
> 
> i have no time now but keep in mind that we also have a multiplier (the 
> system is set up to use ratios / fractions, not hard coded numbers

Many thanks for your reply, Hans.

Although optical bounds in OpenType and character protrusion are very
similar in their goals, I think they are different.

Some glyphs need optical bounds, such as in the following example:

Hanging diacritics seems to be a typographic practice in the Greek
tradition. In poetry, uppercase letters with diacritical marks at the
beginning of the verse are aligned as if they had no diacrical mark
(https://cloud.disroot.org/s/23wXgw2FHN9CHtM).

The only way to achieve it is the use of the lfbd tag. But if the values
are recalculated, it is impossible to get the desired results. It is
impossible to make the desired glyphs work as expected.

> also, it makes no sense to experiment too much with only some demo fonts 
> with incomplete coverage ... adapting the low level mechanism to just 
> one font with one character protruding makes no sense (one can tnen 
> better use the non-opbd way)

I love character protrusion and I avoid optical bounds as much as I can
(I used the Linux Libertine font because you used it, I would never use
optical bounds with Linux Libertine).

But there are some cases in which optical bounds are needed and their
values shouldn’t be altered.

Would it be possible that ConTeXt deploys the optical bound values
exactly from the font without multiplying them?

If the font has wrong values, and character protrusion should be the
solution there.

Many thanks for your help,

Pablo
-- 
http://www.ousia.tk
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If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
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