Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!elroy.jpl.nasa.gov!decwrl!adobe!heaven!glenn
From: glenn@heaven.woodside.ca.us (Glenn Reid)
Newsgroups: comp.lang.postscript
Subject: Re: How do I draw a depth-cued line in PostScript?
Keywords: nope
Message-ID: <555@station.woodside.ca.us>
Date: 28 Jun 91 01:08:46 GMT
References: <1991Jun27.164001.2435@engage.pko.dec.com>
Sender: glenn@heaven.woodside.ca.us
Lines: 25


Adam Billyard writes...
>The PostScript imaging model has no notion of variable shading over the
>area to be filled. The metaphor is of opaque paint being pushed through
>a stencil. Display PostScript extends this a little by including
>transparency, ...

Peter Davis writes...
> Really?  How?  I've been working with Display PostScript for a while, and I  
have
> come across nothing that either explicitly or implicitly allows transparency.
> The only way to achieve transparent effects that I know of it to fill with a
> stipple pattern using imagemask, but this is possible in regular as well as
> Display PostScript.
> 
> Can you explain?  This would be very VERY useful.

No, Display PostScript has not been extended to allow transparency.
Neither has Level 2 PostScript.  However, NeXT has added an "alpha
channel" to their window server that permits bit operations that
provide transparency.  Perhaps that's what you're thinking of.

Glenn Reid
RightBrain Software
PostScript / NeXT developers