🚀 go-pugleaf

On 20 Dec 90 13:05:02 GMT, jeffrey@cs.chalmers.se (Alan Jeffrey) said:

	[ ... on how to make TeX produce output for
	a fixed pitch device ... ]

jeffrey> Certainly, in order to produce perfect output you'd have to
jeffrey> produce a device-dependent .dvi file,

No, the device file would still be device independent -- the contents
would be tailored for a specific device. Notice that DVI files are
already now tailored for a specific device (device dependent in your
sense) in two ways: the first is that each DVI file is for a device with
a specific set of fonts, and the second is that it is for a device with
1/65k resolution. If your actual output device does not have that set of
fonts or that resolution the DVI driver has to make some mapping.

To assist in the mapping betwen the idealized device presumed by current
DVI files and the actual one is the reason why virtual fonts exist and a
standard rounding algorithm is being defined.

There is another alternative, and it is to produce a DVI file that is
tailored not for an idealized device but for an actual device, so that
no mapping is required for that actual device. Since the DVI output
would still be device independent in format, one could take the DVI file
tailored for a specific device and map it onto another device, and this
would be more or less successful depending on how similar the devices
were.

The problem with the 1/65K resolution, CM fonts based idealized device
for which DVI files are currently tailored is that it is hard to map
onto lower resolution actual devices, especially those that have fixed
pitch characters and motions, like a CRT or a line printer.

jeffrey> The problem is that TeX is designed for producing books on
jeffrey> 1270dpi and up printers, and it's output is rather compromised
jeffrey> for anything else.  TeX views laser printers as proofing
jeffrey> devices, and doesn't take much effort about precise spacing at
jeffrey> low resolutions.

This is the *goal*, but the actual TeX mechanism is far more general.
The virtual device for which by default TeX output is currently tailored
does indeed map most easily onto a high resolution typesetter, but I
think that it is possible to describe to TeX different output devices.

Note that all this is already true with ditroff, where you have a
something (DESC) like a TFM that gives you the parameters of the
intended output device.  A ditroff output file is device independent, in
that it can be printed on any device, but tailored (optimized) for a
specific device.

TeX is used as the old C/A/T troff is being used, as currently TeX DVI
drivers do what psroff does, mapping a virtual (C/A/Ts are no longer
manufactured :->) device onto real ones. The only advantage of the CM
based, 1/65k virtual device assumed by TeX is that it is richer than the
old C/A/T one.

jeffrey> If you want device dependent .dvi files though, it's not that hard to
jeffrey> get them by a metafont hack that produces letter-widths and kerns at
jeffrey> multiples of the device pixel width (see how the gray font works for
jeffrey> details).  Inter-word spacing would still be at arbitrary precision,
jeffrey> but inter-word jumps aren't nearly as noticable as inter-letter jumps,
jeffrey> as long as you're printing on a variable-pitch printer.

I am not a TeXnician, but I think this is not true. You can do fixed
pitch printing with TeX, both as to fixed width letters and interword
and interline spacing, e.g. for code listings. I reckon that it is time
for TeX to realize its potential as a ditroff, not as a troff tied to
one specific virtual output device to be mapped more or less neatly onto
actual devices.
--
Piercarlo Grandi                   | ARPA: pcg%uk.ac.aber.cs@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcsun!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk