Re: setrgbcolor with lineto/curveto

From	JohnF <john@please.see.sig.for.email.com>
Newsgroups	comp.lang.postscript
Subject	Re: setrgbcolor with lineto/curveto
Date	2012-06-19 08:12 +0000
Organization	PANIX Public Access Internet and UNIX, NYC
Message-ID	<jrpc8q$o1h$1@reader1.panix.com> (permalink)
References	<jra5b7$mqu$1@reader1.panix.com> <e541e1bb-8ccd-4742-b96f-ab48ee60c0a7@googlegroups.com> <jrp82q$m5o$1@reader1.panix.com> <abf9fc36-51db-4d7f-9531-e5bd7b23f0e5@googlegroups.com>

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gernot.hoffmann@hs-emden-leer.de wrote:
> JohnF wrote:
>> gernot hoffmann wrote:
>> > Below a simple solution, using basic Bezier definitions.
>> > 
>> > http://www.fho-emden.de/~hoffmann/bezier18122002.pdf
>> > page 2
>> > 
>> > Best regards --Gernot Hoffmann
>> 
>> Thanks a lot for your help again, Prof. Hoffmann (I recall your
>> previous help in comp.graphics.algorithms, which was regarding
>> the same little decorative program www.forkosh.com/lineart.html
>> that I'm further modifying now).
>> 
>> I took your solution and simplified it a bit as illustrated below,
>> replacing bezier curves with straight lines so I could follow your
>> postscript ideas more easily. After that worked, I abstracted your
>> 100-step loop into a function /Coline so that the program can draw
>> many lines,
>>   % X0,Y0=start point, X1,Y1=end point
>>   /X0 1.0 def   /Y0 0.0 def
>>   /X1 0.0 def   /Y1 1.0 def
>>   Coline
>>   /X0 0.0 def   /Y0 0.0 def
>>   /X1 1.0 def   /Y1 1.0 def
>>   Coline
>> So the example below just draws a big X. Ultimately, the program
>> will first generate your "stub" at top, followed by many, many,
>> many X0,Y0,X1,Y1 lines. Then I'll re-introduce your original /Func
>> (and /Coeff and control points) for bezier curveto's.
>> Thanks again, John (sig and email at bottom)
>> -----
>> 
>> %!PS-Adobe-3.0  EPSF-3.0
>> %%BoundingBox:  0 0 340 340
>> %%Creator:      Gernot Hoffmann
>> %%Title:        Color interpolation along line
>> %%CreationDate: June 15 / 2012
>> 
>> % Bezier Reference:
>> % http://www.fho-emden.de/~hoffmann/bezier18122002.pdf
>> % page 2
>> 
>> % RGB0=Start color, RGB1=End color
>> /R0 0.0 def   /G0 0.5 def   /B0 0.0 def
>> /R1 1.0 def   /G1 0.5 def   /B1 0.0 def
>> 
>> % number of steps
>> /N 100 def % e.g. 100 subdivisions
>> /dt 1 N div def
>> 
>> /Ipol % color interpolation R = (R1-R0)*t + R0, similarly for G,B
>> {/r R1 R0 sub t mul R0 add def
>>  /g G1 G0 sub t mul G0 add def
>>  /b B1 B0 sub t mul B0 add def
>>  r g b setrgbcolor
>> } def  
>> 
>> /Func % straight line x = (X1-X0)*t + X0, similarly for y
>> {/x X1 X0 sub t mul X0 add def
>>  /y Y1 Y0 sub t mul Y0 add def
>> } def
>> 
>> /Coline % color line
>> {/t 0 def
>>  Func
>>  N
>>  { 
>>   Ipol
>>   x y moveto
>>   /t t dt add def 
>>   Func 
>>   x y lineto stroke
>>  } repeat 
>> } def
>> 
>> /mm {2.834646 mul} def        
>> 100 mm 100 mm scale
>> 
>> 0.1 0.1 translate
>> 
>> % black axis lines
>> 0.001 setlinewidth
>> 0 0 moveto 1 0 lineto stroke
>> 0 0 moveto 0 1 lineto stroke
>> 
>> % color lines
>> 0.01 setlinewidth
>> 
>> % X0,Y0=start point, X1,Y1=end point
>> /X0 1.0 def   /Y0 0.0 def
>> /X1 0.0 def   /Y1 1.0 def
>> Coline
>> 
>> % X0,Y0=start point, X1,Y1=end point
>> /X0 0.0 def   /Y0 0.0 def
>> /X1 1.0 def   /Y1 1.0 def
>> Coline
>> 
>> showpage 
>> 
>> -----
> 
> John,
> thanks for the feedback. Feel free to modify anything.
> 
> My programming style ignores widely special PostScript
> features, because it is based on named variables instead
> of immediate stack operations. This improves understanda-
> bility for non-PS-experts...
> 
> Best regards --Gernot Hoffmann

Yes, you definitely succeeded improving understandability.
I have a vanishingly small knowledge of postscript (and that's
approaching zero from the negative side), but your style allowed
me to pretty easily guess what to do in order to get what I wanted.
(The PLRM's so long and wordy that I pretty much put it aside
 on my ever-growing "to do" list. I also came across the shorter
    http://www-cdf.fnal.gov/offline/PostScript/BLUEBOOK.PDF
 but that's still pretty long, too.)

And, as I think you were hinting, I realize this should probably
be rewritten to use the stack like
   0.0 0.0 1.0 1.0 Coline
rather than using your more instructive named variables like
   /X0 0.0 def   /Y0 0.0 def
   /X1 1.0 def   /Y1 1.0 def
   Coline
which I'll probably get around to doing before changing
the C program that will actually use this stuff.

And I also especially like your
   /mm {2.834646 mul} def        
   100 mm 100 mm scale
notation, making the conversion just look like units following
the number. Thanks again,
-- 
John Forkosh  ( mailto:  j@f.com  where j=john and f=forkosh )

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setrgbcolor with lineto/curveto JohnF <john@please.see.sig.for.email.com> - 2012-06-13 13:41 +0000
  Re: setrgbcolor with lineto/curveto Helge Blischke <h.blischke@acm.org> - 2012-06-13 16:16 +0200
    Re: setrgbcolor with lineto/curveto JohnF <john@please.see.sig.for.email.com> - 2012-06-13 16:04 +0000
    Re: setrgbcolor with lineto/curveto Odysseus <odysseus1479-at@yahoo-dot.ca> - 2012-06-13 20:20 -0600
      Re: setrgbcolor with lineto/curveto JohnF <john@please.see.sig.for.email.com> - 2012-06-14 04:05 +0000
      Re: setrgbcolor with lineto/curveto luser- -droog <mijoryx@yahoo.com> - 2012-06-16 14:45 -0700
  Re: setrgbcolor with lineto/curveto luser- -droog <mijoryx@yahoo.com> - 2012-06-13 16:20 -0700
    Re: setrgbcolor with lineto/curveto luser- -droog <mijoryx@yahoo.com> - 2012-06-13 17:16 -0700
      Re: setrgbcolor with lineto/curveto luser- -droog <mijoryx@yahoo.com> - 2012-06-13 17:36 -0700
        Re: setrgbcolor with lineto/curveto JohnF <john@please.see.sig.for.email.com> - 2012-06-14 04:11 +0000
          Re: setrgbcolor with lineto/curveto luser- -droog <mijoryx@yahoo.com> - 2012-06-14 09:05 -0700
  Re: setrgbcolor with lineto/curveto gernot.hoffmann@hs-emden-leer.de - 2012-06-16 11:00 -0700
  Re: setrgbcolor with lineto/curveto gernot.hoffmann@hs-emden-leer.de - 2012-06-16 10:55 -0700
    Re: setrgbcolor with lineto/curveto gernot.hoffmann@hs-emden-leer.de - 2012-06-16 11:23 -0700
    Re: setrgbcolor with lineto/curveto JohnF <john@please.see.sig.for.email.com> - 2012-06-19 07:00 +0000
      Re: setrgbcolor with lineto/curveto gernot.hoffmann@hs-emden-leer.de - 2012-06-19 00:34 -0700
        Re: setrgbcolor with lineto/curveto JohnF <john@please.see.sig.for.email.com> - 2012-06-19 08:12 +0000
  Re: setrgbcolor with lineto/curveto John Deubert <john@acumentraining.com> - 2012-06-30 10:20 -0700
    Re: setrgbcolor with lineto/curveto JohnF <john@please.see.sig.for.email.com> - 2012-07-04 03:07 +0000
      Re: setrgbcolor with lineto/curveto luser- -droog <mijoryx@yahoo.com> - 2012-07-05 16:24 -0700
        Re: setrgbcolor with lineto/curveto JohnF <john@please.see.sig.for.email.com> - 2012-07-06 14:23 +0000
          Re: setrgbcolor with lineto/curveto JohnF <john@please.see.sig.for.email.com> - 2012-07-11 01:57 +0000
        Re: setrgbcolor with lineto/curveto tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2012-07-11 01:08 -0400
          Re: setrgbcolor with lineto/curveto luser- -droog <mijoryx@yahoo.com> - 2012-07-12 03:12 -0700
            Re: setrgbcolor with lineto/curveto tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2012-07-12 22:20 -0400

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