[NTG-context] fluctuating baseline of header text

j. van den hoff veedeehjay at googlemail.com
Sat Dec 27 15:07:31 CET 2014

On Sat, 27 Dec 2014 13:36:49 +0100, Hans Hagen <pragma at wxs.nl> wrote:

> On 12/27/2014 12:16 PM, j. van den hoff wrote:
>> On Sat, 27 Dec 2014 10:40:30 +0100, Pablo Rodriguez <oinos at gmx.es>  
>> wrote:
>>> On 12/26/2014 11:32 PM, j. van den hoff wrote:
>>>> [...]
>>>> in this example (and with this font) the problem is only occuring when
>>>> toggling between pages 6/7 or 7/8 (at sufficient zoom it's easy to  
>>>> see),
>>>> i.e.the header is shifted downward on page 7. in other docs with
>>>> different
>>>> fonts it happens across multiple pages. my guess would be it has to
>>>> do with the digit heights in the different fonts and the fact that the
>>>> page numbers are much larger than the heading, but that's only a  
>>>> guess.
>>>> can someone confirm the problem?
>>> Hi Jörg,
>>> this sample shows the issue without zooming:
>> thanks for confirming this. @devs: can this be considered "misbehaviour"
>> (not to call it a bug ;-)) or is it somehow unavoidable?
> it's not a bug at all .. you just get what you ask for

good to know.

> \showframe \showglyphs
> your header is too small so what you want only works if the heights  of  
> all characters are the same which is not the case here

well this seems not to be the whole explanation AFAICS. it might be  
correct for pablo's
example, but for my original example, which is equivalent to:

\setupheader      [style=\smallbodyfont\ss\it]
\setupheadertexts [section]
\setuppagenumbering[location={header,margin}, style=\bfc]


I can't see that the header space is to small, no? or what am I missing?  
using `\showglyphs' (which I didn't know of: thanks),
it still looks to me as if the problem is caused by the fact, that all  
positions are measured from the top and
the header line's baseline is aligned with the baseline of the large page  
numbers glyph boxes (although only approximately so, as far
as I can tell on my monitor...) where -- for the default font -- the  
glyphbox of the `7' has a larger vertical extension than the others
(so that it extends a bit further down as measured from the top) which  
causes the baseline of the header to shift downwards accordingly.


> solutions:
> - use a proper height for the header
> - package the header text in a box and set the height of that box
>>>     \setuppapersize[A8]
>>>     \setupheader      [style=\itx\ss]
>>>     \setupheadertexts [section]
>>>     \setuppagenumbering[location={header,margin}, style=\bfd]
>>>     \starttext
>>>     \dorecurse{80}{\section{Introduction}
>>>     bla\page[yes]}
>>>     \stoptext
>>> When the glyph 7 is involved in page number, baseline is a bit lower.  
>>> As
>>> you wrote, I guess this is related with the glyph metrics.
>> yes. this seems to be supported by the fact that it happens differently
>> (usually more frequently) with other fonts.
>> joerg
>>> Just in case it helps,
>>> Pablo

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