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From: schoett@lan.informatik.tu-muenchen.dbp.de (Oliver Schoett)
Newsgroups: comp.text
Subject: Re: SliTeX fonts
Summary: Pixel files are necessary for invisible fonts
Keywords: TeX, Metafont
Message-ID: <177@infovax.lan.informatik.tu-muenchen.dbp.de>
Date: 13 Jul 88 09:42:27 GMT
References: <330@marob.MASA.COM> <12395@mimsy.UUCP>
Reply-To: schoett@lan.informatik.tu-muenchen.dbp.de (Oliver Schoett)
Organization: Inst. fuer Informatik, TU Muenchen, W. Germany
Lines: 31

In article <12395@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
> [Invisible fonts do not need a PK or GF or PXL file, because all a
> device driver needs to know about them is the size of the bounding
> box for each character, and that information is also present in the
> fonts' TFM file.]

This is not quite right.

METAFONT occasionally creates character bitmaps whose dimensions do
not match the (rounded) ideal measurements given in the TFM file.  For
example, in a nice lower-case 'm' the three stems should have an equal
number of pixels, and so should the gaps between them.  To accommodate
this, the size of the resulting bitmap may have to be changed slightly
from the (rounded) ideal value.  This is described on p. 102 f. of the
METAFONTbook.  An application is the CMR roman lower-case 'm' on page
332 f. of "Computer Modern Typefaces".

Information about the bitmap size for a certain resolution is
contained in PK, GF, or PXL files.  Device drivers should base their
character positioning on the bitmap size as well as the TFM size of
each character (the max_drift algorithm), and thus the bitmap size is
required even for invisible fonts.

I wish more device drivers would actually use the max_drift algorithm!


Oliver Schoett

schoett@lan.informatik.tu-muenchen.dbp.de
schoett%lan.informatik.tu-muenchen.dbp.de@
			{relay.cs.net, unido.uucp, ddoinf6.bitnet}