On 3/13/2020 3:16 PM, Marcel Fabian Krüger wrote:
On Thu, Mar 12, 2020 at 06:43:39PM +0100, Hans Hagen wrote:
This seems inconsistant. Is there a reason why this would be required or
could it be changed to handle height and depth consistently?
It is (among some others) a known artifact that dates from the very early
days when we played with alternative par builders and such. These offsets
were introduced when we were messing around with arabic and had to handle
marks and at the same time deal with tex's perspective on line dimensions
(which it doesn't really have): prevdepth, maxdepth and such so this is
(irr) why we handled the depth differently.
Because in the process more access to node lists at various stages was
implemented one can indeed wonder if we need to keep this assymetrical
approach (as we were never really bitten by it there was not real reason to
change is, also because it can resuel in incompatible output.)
Anyway, what I can do is change it in luametatex so that for a longer period
we can see if context users run into issues and complain about a change in
output (i can then quickly revert to make it some option). After all,
context users know that they are possible victims of testing.
Just changing something in luatex right away is no option given the demand
for stability, and definitely not in code freeze time. When we don't run
into problems we can then decide to do it in luatex too (assuming that
complaints about different output don't backfire).
Another option is to introduce a parameter \characteroffsetmode:
0 = no compensation
1 = ht compensation (current and default)
2 = dp compensation
3 = ht and dp compensation
IMHO such a parameter sounds like a good idea. Another approcach I could
think of would be to assign some unused bits in the glyph subtype to
control this on a glyph-by-glyph basis. Especially that could help if
there are some weird fonts which set up their glyphs in odd ways and
would cause trouble if compensation is applied.
redefining the subtype is definitely something incompatible because
those bits in the subtype are 'free to use' so not for the engine to
take ... weird fonts cans be dealt with using virtual font entries ... so:
a future release (1.13) will have this
\startsubsection[title={\type{\glyphdimensionsmode}}]
Already in the early days of \LUATEX\ the decision was made to calculate the
effective height and depth of glyphs in a way that reflected the applied
vertical
offset. The height got that offset added, the depth only when the offset was
larger than zero. We can now control this in more detail with this mode
parameter. An offset is added to the height and|/|or subtracted from the
depth.
The effective values are never negative. The zero mode is the default.
\starttabulate[|l|pl|]
\DB value \BC effect \NC\NR
\TB
\NC \type {0} \NC the old behavior: add the offset to the height and
only subtract
the offset only from the depth when it is positive
\NC \NR
\NC \type {1} \NC add the offset to the height and subtract it from the
depth \NC \NR
\NC \type {2} \NC add the offset to the height and subtract it from the
depth but
keep the maxima of the current and previous results
\NC \NR
\NC \type {3} \NC use the height and depth of the glyph, so no offset is
applied \NC \NR
\LL
\stoptabulate
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Hans Hagen | PRAGMA ADE
Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
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