Path: utzoo!mnetor!uunet!mcvax!ukc!eagle!icdoc!qmc-cs!liam
From: liam@cs.qmc.ac.uk (William Roberts)
Newsgroups: comp.lang.postscript
Subject: Re: psdraft
Message-ID: <464@sequent.cs.qmc.ac.uk>
Date: 6 May 88 19:44:16 GMT
References: <8996@sol.ARPA> <9078@sol.ARPA> <840@zippy.eecs.umich.edu> <5847@well.UUCP>
Reply-To: liam@cs.qmc.ac.uk (William Roberts)
Organization: Computer Science Dept, Queen Mary College, University of London, UK.
Lines: 49
Keywords: setgray, opaque ink
Summary: PostScript colours are OPAQUE
Sender:


In article <5847@well.UUCP> samlb@well.UUCP (Samuel B. Bassett) writes:
>I'd try 0.8 (0.7, 0.6...) setgray until the underlying text shows through
>the draft, if I were in your shoes . . .
Fun maybe - but you definitely won't make any profit with such
a fundamentally incorrect understanding of PostScript!

It won't work: PostScript "ink" is logically opaque, whatever
the "colour" applied, so there will never be anything visible
underneath.

The problem of "how do I print the gray text at beginning of page"
is easy and is solved in two stages:

1) Change "showpage" so that it becomes

        /showpage { showpage do_grey_text } bind def

   and thereby do your grey text immediately at the beginning
   of all pages except the very first (NB: do_grey_text is
   probably not the actual routine name...)

2) Notice that the psdraft stuff is being inserted before the
   any of the actual printing commands in the PostScript
   document, so just print the grey text directly at the end of
   the PostScript code inserted by psdraft

Note for purists: the second step actually causes printing
within the Prologue and so breaks the document structuring
conventions. To do this properly would involve adding the
do_grey_text (or whatever) immediately after the first %%Page comment


The only approved way of laying down black dots in some kind of
stipple pattern without filling the white around them is to use
the "imagemask" primitive and a stipple bit pattern. This is
like "image" applied to a 1 bit-per-pixel raster, except that
only the "black" pixels are painted. The clipping region
applies, so you can clip to the outline of the text, but you
will have to do your own tesselation.

The unapproved way (used extensively by the Macintosh) is to
change the halftone screen using "setscreen", but this isn't
properly portable between printers as it depends on the printer
pixel size etc.
-- 

William Roberts         ARPA: liam@cs.qmc.ac.uk  (gw: cs.ucl.edu)
Queen Mary College      UUCP: liam@qmc-cs.UUCP
LONDON, UK              Tel:  01-975 5250