[Groff] Placement problem with coloured circles in pic

[Ted Harding]

Greetings all!

The folloowing exemplifies a placement problem I am
experiencing when creating coloured circles in pic.
This is just a simple example: my ultimate intention
is to be able to place a circle of arbitrary size
and arbitrary colour, define by "RGB", at an arbitrary
point.

.PS
line from (-2,0) to (2,0)
line from (0,-2) to (0,2)
define cblob {
  command sprintf(".defcolor COL rgb %.3ff %.3ff %.3ff.sp 2",$4,$5,$6)
  circle rad $1 at ($2,$3)  coloured "COL"
}

circle rad 1 at (0,0)  ## First (black outline) circle (see below)
for i=0 to 20 do{      ## 2nd (i=0), 3rd (i=1) ... green circles.
  r = (1 - i/20) 
  cblob(r,0,0, 0,r,0)
}
.PE

The first (plain black outline) circle is correctly placed
with its centre at (0,0).

The second (pure green circle corresponding to i=0) is
displaced some distance above the point (0,0).

The third (slightly smaller greenish circle corresponding to i=1)
is displaced much further above (0,0).

All subsequent circles appear to have their centres at the
centre of the third circle, so from i=1 onwards things are
as they should be apart from being centred in the wrong place.

I'm puzzled about why the r=0 and r=1 circles get displaced!

Any comments?
Ted.


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E-Mail: (Ted Harding) <address@hidden>
Date: 05-Jul-2012  Time: 21:33:27
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