On Mon 9th Aug, 2010 at 18:57, Lars Hellström seems to have written:
Dr. Clea F. Rees skrev:
I'm trying to generate support files for a new maths font using
fontinst and I've run into the following problem. I can recreate the
problem using cmex10 so I don't think it is a font issue but, rather,
either a fontinst issue or a me issue.
Suppose I reencode cmex10:
...
\transformfont{cmex10-omx}{\reencodefont{omx}{\fromafm{cmex10}}}
Taking cm metrics from AFM files is usually to be asking for trouble: glyph
names may be off, bounding boxes need not yield the proper metrics, and so
on. May I however assume that you know this and are using \fromafm{cmex10}
only because it's what you'd have to do for the other font?
Yes. At least, I hadn't really thought about the general issue for cm
fonts but I was only doing this because it shadowed what I needed to do
for IrianisADFMath. I am not actually trying to take metrics from cm
AFMs in order to use them. I was just trying to understand what was
happening with Irianis.
...
and then install as follows:
\installfont{cmex7v10}{cmex10-omx,mathex}{omx}{OMX}{cmex}{m}{n}{}
...
[Note: this will actually trigger many errors but simplifies what's
happening.]
Then for certain characters, I will get a very large negative depth
From what you've written later, I conclude these characters are not the
delimiter characters (for which it is traditional to have large depths)...
And I should of course have understood that from the start, as the depths of
those are normally /positive/ (corresponding to a negative y-coordinate of
the bottom side of the bbox). Your situation is that the depths are
/negative/, which corresponds to a positive y-coordinate of the bottom side
of the bbox, as would indeed be expected for a straightforward accent.
Yes.
which causes TeX to position maths accents incorrectly. For example an
excerpt from the vpl file:
(CHARACTER D 98 (COMMENT hatwide)
(CHARWD R 0.555)
(CHARHT R 0.744)
(CHARDP R -0.562)
(MAP
(SETCHAR D 98) (COMMENT hatwide)
)
(NEXTLARGER D 99) (COMMENT hatwider)
)
(CHARACTER D 99 (COMMENT hatwider)
(CHARWD R 1.0)
(CHARHT R 0.772)
(CHARDP R -0.575)
(MAP
(SETCHAR D 99) (COMMENT hatwider)
)
(NEXTLARGER D 100) (COMMENT hatwidest)
)
(CHARACTER D 100 (COMMENT hatwidest)
(CHARWD R 1.444)
(CHARHT R 0.772)
(CHARDP R -0.575)
(MAP
(SETCHAR D 100) (COMMENT hatwidest)
)
)
The effect of this is to position the accents on the baseline. But
unfortunately, TeX expects the accents to be positioned correctly for a
letter of height x. The upshot is that accents end up in the middle of
letters.
Well, that's actually a different matter; TeX uses a different method for
accent placement in math (just stack things in a vbox, with kerns to adjust
vertical position of accent to letter, but no \baselineskip or similar) than
in text, and the math method is sensitive to the depths of accent characters.
I see this for maths accents in oml.etx, omx.etx and msbm.etx, at
least. It doesn't occur for accents in ot1.etx even though these have
similar-looking bounding box statements in the afm files. For example,
hatwide, hatwider, hatwidest, tildewide, tildewider, tildewidest and
vector are definitely affected and probably tie, as well. But caron,
hat etc. are fine.
I have been trying to figure this out for a while. Karl Berry pointed
out the large negative depth I'm seeing in the tfm files for the new
font as opposed to the absence of such a depth in the tfm for cmex10.
That prompted me to experiment a little. I don't get the large negative
depth if I use afm2pl rather than fontinst
This could be a matter of afm2pl not ever making the depth negative, but
that's just a guess.
but I'm not sure how to get
varchar and nextlarger etc. using that method. But I do get the issue
if I start with cmex10.afm and not just with the new font.
If anybody can cast any light on this, that would be great. Right now
I'm working on a work-around but it is not terribly elegant.
Senare skrev Dr. Clea F. Rees:
A couple of days ago, I noted that fontinst causes problems with the
placement of maths-specific accents.
Is this because newlatin.mtx contains this:
\foreach(accent){grave,acute,circumflex,tilde,dieresis,hungarumlaut,%
ring,caron,breve,macron,dotaccent}
\ifisglyph{\str{accent}}\then
\resetglyph{\str{accent}}
\glyph{\str{accent}}{1000}
\resetdepth{0}
\endresetglyph
\Fi
\endfor(accent)
but there is no similar code in mathit.mtx (for OML) or mathex.mtx (for
OMX) and no metrics file at all for MSBM?
Precisely! latin.mtx/newlatin.mtx are used to generate OT1 fonts, which would
traditionally be the source of "basic" accents in math, so they these files
had to make them conform to this technical requirement. This dates back to
fontinst 1.314, 27 January 1994.
From the list of changes, Alan doesn't seem to have done anything to
mathex.mtx after fontinst 1.305 (9 January 1994) however, and I've only done
some bugfixes (back in 2000). Hence it merely seems noone has gotten around
to fixing this yet! Code contributions are welcome.
I was wondering about just adding the code from newlatin.mtx to
mathit.mtx, mathex.mtx and some metrics file for msbm and altering this
list of accents appropriately but I wasn't sure if there might not be
some reason this shouldn't be done.
A factor that might have been hiding it is that if you "copy" a glyph using
the idiom
\setglyph{new}
\glyph{old}{1000}
\endsetglyph
then \depth{new} will be \max{\depth{old}}{0}; the same happens if you
similarly try to adjust the vertical position of the accent. It is only for
raw glyphs that you might get a negative depth.
Interesting. vector is renamed in my set up using \renameglyph but that
obviously does not have the same effect.
This isn't a big deal for me because the font I've got puts the accents
(at least the wide ones) in the wrong place anyway (relative to TeX's
expectations, at least) - so even if fontinst did the right thing, the
metrics would still have to be corrected. But I thought it might be
helpful to add similar code to the metrics files for maths, if anybody
would be willing to do that.
Also, I would like to know whether I am aware of the list of maths
accents. At the moment, I am correcting depth for:
vector
tie [not sure whether I should be in this case or not]
I don't think that is used as a math accent, so no, but OTOH it hardly hurts.
hatwide
hatwider
hatwidest
tildewide
tildewider
tildewidest
If anybody could confirm this list is complete (w/ or w/o tie) or tell
me if I've missed something, I would be very grateful.
I suppose this is the kind of information for which one would consult the
relevant encoding specifications. Too bad several of those haven't been
written yet. :-(
Thanks very much for all your answers,
Clea
