[R] getting lines with non-rounded caps?

[Yves Gauvreau]

Since the guy wants flat ends wouldn't it be simpler and more portable to
use directly filled rectangles (rect) instead of lines?

Just a thought

Yves Gauvreau


----- Original Message -----
From: "Prof Brian Ripley" <ripley at stats.ox.ac.uk>
To: <xyzzy at speakeasy.org>; <paradis at isem.univ-montp2.fr>
Cc: <r-help at stat.math.ethz.ch>
Sent: Wednesday, September 20, 2000 6:16 AM
Subject: Re: [R] getting lines with non-rounded caps?


>
> > Date: Wed, 20 Sep 2000 10:50:08 +0200
> > To: Trent Piepho <xyzzy at speakeasy.org>
> > From: Emmanuel Paradis <paradis at isem.univ-montp2.fr>
> > Subject: Re: [R] getting lines with non-rounded caps?
> > Cc: r-help at stat.math.ethz.ch
> >
> > At 11:31 19/09/00 -0700, you wrote:
> > >I'm trying to get a plot with wide lines that don't have rounded end
caps.
> > >You can see the effect quite clearly with a plot like this:
> > >
> > >plot(0:1)
> > >lines(c(1.5,1.5),c(0,.5),lwd=20,col="red")
> > >lines(c(1.5,1.5),c(.5,1),lwd=20,col="green")
> > >abline(h=0)
> > >abline(h=0.5)
> > >abline(h=1)
> > >
> > >The colored lines should be between the horizontal lines, but because
of the
> > >rounded end caps, they aren't.
> > >
> > >Under X11, if I set lty to something like "F0", the end caps are turned
off.
> > >Unfortunately, the "0" appears to get ignored, and the line style is
the same
> > >as "FF", i.e. 16 units of drawn line, then 16 units of space.
> > >
> > >With the postscript device, lines styles like "FF" still get rounded
end
> > caps,
> > >unlike X11.
> >
> > Hi,
> >
> > This is a behaviour I already noticed under Windows NT when using
plot(...,
> > type="h", lwd=10), so that the thickness of the lines is expanded all
> > around their starting- and end-points, rather than only perpandicularly
to
> > the lines (which was what I expected). A workaround for the example you
> > give is to use rect()
>
> It may be what you expected, but it is not what normally happens in
> computer graphics.  The idea is that the line is drawn with a round pen
> of radius lwd.  If you use a flat-ended pen, you get problems when a
> line changes direction discontinuously (and polylines do), as the
> line appears half-broken on the outside.
>
> PostScript has different options for the internal changes of
> direction (setlinejoin) and the ends (setlinecap).  So does X11, and I
> see that the devX11 device uses JoinRound, and CapRound if lty=0
> otherwise CapButt.
>
> Is there a case for adding cap-style and join-style to the line type
options?
> I am not sure if all the devices could support them.  In particular,
> I don't know if it is possible to achieve different internal and
> end effects under the Windows graphics model.
>
> --
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272860 (secr)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>
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