🚀 go-pugleaf

On 28 Dec 90 00:33:06 GMT, ken@csis.dit.csiro.au (Ken Yap) said:

ken> In article <PCG.90Dec25224617@teachk.cs.aber.ac.uk>:

pcg> The virtual device for which by default TeX output is currently
pcg> tailored does indeed map most easily onto a high resolution
pcg> typesetter, but I think that it is possible to describe to TeX
pcg> different output devices.  [ ... ] You can do fixed pitch printing
pcg> with TeX, both as to fixed width letters and interword and
pcg> interline spacing, e.g. for code listings. I reckon that it is time
pcg> for TeX to realize its potential as a ditroff, not as a troff tied
pcg> to one specific virtual output device to be mapped more or less
pcg> neatly onto actual devices.

ken> In summary: 1. I do not see that rounding from scaled points to real
ken> device resolution is any sort of limitation so I don't see that we have
ken> to follow the ditroff path, and 2. Quantizing TeX's spacings requires
ken> only some work with fonts and macros.  Character substitution should
ken> use virtual fonts of course.

I think that we have written exactly the same thing here. Haven't we?

ken> But here's the gist of my argument: Piercarlo argues about the
ken> 1/65k pt resolution of TeX's ideal device as if it were a
ken> limitation.

Well, it virtually ensures that quantizing will be approximate, even if
by very little. 1/65k of a point is an exceedingly fine resolution, and
even if the real device resolution is not (as it is *very* rarely) a
factor of 1/65k, the resulting error is usually negligible.

Ditroff though avoids even this negligible source of errors by being
parametric with respect to the actual hirzontal and vertical resolutions
of the intended output device, and ensuring that all motions and sizes
are in fact even multiples of these resolutions, and by declaring in its
output for which resolutions all motions and sizes are meant.

ken> In fact since no actual device exists with this resolution, it is
ken> misleading to say that TeX is tailored to "one specific virtual
ken> output device"

A nit: this is is not misleading, it is entirely accurate. The one
specific virtual output device is the one for which DVI files are
encoded currently; historically, as I remarked (and you repeated), DVU
files were tailored not just for 1/65k resolution, but also for the CM
font layout (dependent on obscure Stanford conventions), and both the
resolution and the font layout had to be mapped onto those for the real
device. The recent introduction of virtual fonts has been motivated
precisely by the desire to alleviate the font layout mapping problem, to
accomodate non CM fonts more easily.

Fortunately TeX can be taught about different fonts and to calculate its
output so that coordinates are quantized to look good on other, real,
devices, thus making it unnecessary to have DVI rounding standards
(except if you are, as yopu should not, printing to a real device
different from the one for which the DVI file was optimized).

ken> In fact, no such device is likely to be made: near beginning of the
ken> TeXbook we read that 1/65k pt is a length comparable to the
ken> wavelength of light.

What about using TeX to drive electron beam chip etching devices? What
about a Conway&Mead set of TeX macros? Can silicon TeX compilation be
that far off?

:-) :-) :-)
--
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