Re: [Groff] A tip for arbitrary colours in PIC

[Ted Harding]

And, finally (for the moment -- more to come when I've thought
about some aspects a bit more) here is an example for colouring
in nested polygons (such as might be used for a contour plot).

The trick here is defining a function "mkpoly" in PIC to construct,
within troff, a string variable \*[poly] which contains the
displacements vector for the "\D'P ...'" command to troff.
This is then invoked from PIC with

  "\D'P \*[poly]'" at (<wherever>)

where <wherever> is the starting-point from which "\D'P ... '" draws.

The following example draws a series of four 8-sided approximations
to ellipses, nested within each other and with different colours.

8<-------------------------------------------------

.PS 5i
start=1
define mkpoly {
  if start then {
    command sprintf(".ds poly \"\" ")
    start = 0
  }
  command sprintf(".ds poly \*[poly] %.3fi %.3fi",$1,$2)
}

line from (0,0) to (5,0) to (5,5) to (0,5) to (0,0)
start=1
copy thru mkpoly until "EOT"
-0.439  0.707
-1.061  0.293
-1.061 -0.293
-0.439 -0.707
 0.439 -0.707
 1.061 -0.293
 1.061  0.293
 0.439  0.707
EOT
"\X' ps: exec 0.0 1.0 0.0 setrgbcolor'"
"\D'P \*[poly]'" at (4.0,2.5)

start=1
copy thru mkpoly until "EOT"
-0.330  0.530
-0.795  0.220
-0.795 -0.220
-0.330 -0.530
 0.330 -0.530
 0.795 -0.220
 0.795  0.220
 0.330  0.530
EOT
"\X' ps: exec 0.7 0.3 0.0 setrgbcolor'" 
"\D'P \*[poly]'" at (3.75,2.5)

start=1
copy thru mkpoly until "EOT"
-0.220  0.354
-0.530  0.146
-0.530 -0.146
-0.220 -0.354
 0.220 -0.354
 0.530 -0.146
 0.530  0.146
 0.220  0.354
EOT
"\X' ps: exec 0.85 0.2 0.0 setrgbcolor'"
"\D'P \*[poly]'" at (3.60,2.5)

start=1
copy thru mkpoly until "EOT"
-0.110  0.1768
-0.265  0.0732
-0.265 -0.0732
-0.110 -0.1768
 0.110 -0.1768
 0.265 -0.0732
 0.265  0.0732
 0.110  0.1768
EOT
"\X' ps: exec 1.00 0.0 0.75 setrgbcolor'"
"\D'P \*[poly]'" at (3.50,2.5)
.PE

8<-------------------------------------------------

For example, the value of "\*[poly]" in the last case is

"-0.110  0.1768 -0.265  0.0732 -0.265 -0.0732 -0.110 -0.1768 \
0.110 -0.1768  0.265 -0.0732  0.265  0.0732  0.110  0.1768"



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E-Mail: (Ted Harding) <address@hidden>
Fax-to-email: +44 (0)870 094 0861
Date: 13-Sep-09                                       Time: 16:27:56
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