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Re: [Groff] Problems with arcs and angles


From: John Gardner
Subject: Re: [Groff] Problems with arcs and angles
Date: Tue, 9 May 2017 21:42:03 +1000

Fair enough.

Well, the grops code worked for me too
<https://github.com/Alhadis/language-roff/commit/ec8e287cb35f7a91924e02e09af68202d8cddade>,
actually.

Thanks to everybody again for their help. =)



On 9 May 2017 at 21:23, Deri James <address@hidden> wrote:

> On Tue 09 May 2017 13:55:38 John Gardner wrote:
> > Looks like there's a mistake in groff_out(5). It describes its
> arc-drawing
> > command as:
> >
> > *Draw arc from current position to (h1, v1)+(h2, v2) with center at (h1,
> >
> > > v1);*
> >
> > However, gropdf.pl tells a different story. To quote line #2791:
> > <http://git.savannah.gnu.org/cgit/groff.git/tree/src/
> devices/gropdf/gropdf.p
> > l?id=453a8aa7c8f8dd0c78160466301f81be8c40df2e#n2791>
> >
> > *Documentation is wrong. Groff does not use Dh1,Dv1 as centre of the
> > circle!*
> >
> > I noticed something odd when drawing an arc which wasn't an evenly-sized
> > quarter-circle. For instance, the following Pic code:
> >
> > .PS
> >
> > > move down
> > > A: box
> > > arc at A.n
> > > line right
> > > .PE
> >
> > ... generates the following output:
> > > …
> >
> > V84000
> >
> > H99000
> >
> > > Da 0 -36000 18000 54000
> >
> > Which looks like this in gropdf and my own canvas code, respectively:
> >
>
> In gropdf I adjust the circle centre using code I found in the geometry.cpp
> library used by the grops driver, so that I could duplicate the output
> produced by grops.
>
>


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