[comp.text] Rhyme or reason in TeX scales

edwards@dogie.macc.wisc.edu (mark edwards) (06/21/89)

 Does anyone have a good explanation how the numbers are derived for the
bitmaped fonts. For instances for for a pxl font with a design size of
10pt at 300dp corresponds to the 1500 directory. But the same font in 
pk format is located at 300, while the font magstep1 is at 360 for pk and
1800 for pxl.

thanks
mark

ken@cs.rochester.edu (Ken Yap) (06/22/89)

| Does anyone have a good explanation how the numbers are derived for the
|bitmaped fonts. For instances for for a pxl font with a design size of
|10pt at 300dp corresponds to the 1500 directory. But the same font in 
|pk format is located at 300, while the font magstep1 is at 360 for pk and
|1800 for pxl.

It's not too complicated, fortunately.

Magsteps form a geometric series. Magstep0 = 1, magstep1 = 1.2,
magstep2 = 1.2 * 1.2 = 1.44, etc. Magstephalf = sqrt(1.2).

For gf and pk files, the number is resolution * factor. Thus
a magstep1 font for a 300 dpi device is 360gf.

For pxl files (who uses them anymore? :-)), the number is
resolution * factor * 5. This was so that a magstep0 font
for a 200 dpi device had a number of 1000.

In some drivers and the TeXbook you will find references to
``magnification''. This is just the magstep factor * 1000.
Thus 1728 is magstep3. For the 200 dpi device mentioned and
pxl fonts, the magnification was reflected in the suffix.

A final note. I've mentioned 360gf, but on some systems the
components are arranged differently to satisfy pathname limitations.
E.g. gf/360/cmr10.