[tex-k] AFM2TFM: are length values handled correctly?

[Frederic LOYER]

On Thu, Sep 27, 2001 at 06:53:29PM +0400, Vladimir Volovich wrote:
> Hi,
> 
> in AFM files, all lengths (e.g. kerns) are expressed in 1/1000 of
> postscript point, and the latter is defined as (1/72 in), i.e. "bp" in
> TeX notation.

One can think of 1000 times the ratio  length/font_size... This ratio
have no unit.

> in TFM files, all lengths are expressed in font design size values,
> and the latter is expressed in TeX points (1/72.27 in), i.e. "pt".

In TFM file, lenghth are coded as multiple of designsize... which 
is the same  length/font_size  ratio. Let's see a tftopl header:

(DESIGNSIZE R 10.0)
(COMMENT DESIGNSIZE IS IN POINTS)
(COMMENT OTHER SIZES ARE MULTIPLES OF DESIGNSIZE)

> therefore, when AFM2TFM converts some length (e.g. kern) to be put
> into TFM (PL or VPL) file, it should multiply the result by
> 72.27/72=1.00375.
> But i did not find such conversion looking into the sources of
> AFM2TFM.
> Is AFM2TFM taking into account the difference between the size of PS
> and TeX points?

In fact, when you ask for a Type 1 font (\font\f=ptmr), TeX see a 10pt
font... and just read length as "pt".  If you mean 10bp
(\font\f=ptmr at 10bp) TeX see a 10pt font scaled 1004 and does the
conversion!

> (and a related question: does dvips handle this difference too?)

It does: a "ptmr" font (at 10 TeX point) is loaded (at 600dpi) by
the following Postscript code:

   83.022 /Times-Roman rf end

83.022 is the font size in pixel, 10*600/72.27.  QED

--
Loyer Frédéric <frederic.loyer@club-internet.fr>