Path: csiph.com!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!border3.nntp.dca.giganews.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!news.giganews.com.POSTED!not-for-mail
NNTP-Posting-Date: Tue, 16 Jul 2013 18:34:45 -0500
From: John Deubert <john@acumentraining.com>
Organization: Acumen Training
Newsgroups: comp.lang.postscript
Date: Tue, 16 Jul 2013 16:34:45 -0700
Message-ID: <2013071616344532779-john@acumentrainingcom>
References: <87fvvfde6v.fsf@Aspire.decebal.nl>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Subject: Re: Rainbow printing
User-Agent: Unison/2.1.10
Lines: 56
X-Usenet-Provider: http://www.giganews.com
X-Trace: sv3-EHoDBvff+sBGQIYvA5/C45hPTFFp+YI57gTIY/U6pEnswkczTSO4rnZjfeXLJPshzb838GVivLlVb/S!JApQiD53BfmY5GE9CxIh7fx/ccObGZEtGMQXYFoIQSe9AIloVqDn+chV6hMe9Xut5ABV
X-Complaints-To: abuse@giganews.com
X-DMCA-Notifications: http://www.giganews.com/info/dmca.html
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly
X-Postfilter: 1.3.40
X-Original-Bytes: 2257
Xref: csiph.com comp.lang.postscript:1462

On 2013-07-15 15:40:24 +0000, Cecil Westerhof said:

> I would like to print things with a rainbow stripe. So the top would
> be red, the bottom would be violet and the other colours would be in
> between. Is it possible to do this?

I'd be inclined to do this with a level 1 technique, using sethsbcolor:

% ========== cut here =============

/center { 300 400 } def

/innerRadius 100 def
/outerRadius 150 def

/innerColor .8 def	% Purple, close enough
/outerColor 0 def	% red

/steps 100 def

/deltaR outerRadius innerRadius sub steps div def
/deltaColor outerColor innerColor sub steps div def


/color innerColor def
deltaR setlinewidth

innerRadius deltaR outerRadius
{
	center 3 -1 roll 0 180 arc
	color 1 1 sethsbcolor
	stroke
	/color color deltaColor add def
} for

showpage

% ========== cut here =============

Not technically as smooth (or nearly as cool) as using smooth shading, 
but gets the job done.

- John


-- 
========
John Deubert
Acumen Training
PostScript & PDF Engineering Classes & Consulting
www.acumentraining.com

Learn PostScript programming techniques
Read the free Acumen Journal
acumentraining.com/acumenjournal.html