Re: drawing commands in groff(7) (was: undiagnosed pic error)

[Deri]

On Tuesday, 6 June 2023 21:07:07 BST G. Branden Robinson wrote:
>     \D'a hc hv h v'
>         Draw circular arc centered at (hc, vc) from the drawing position
>         to (h, v).

Hi Branden,

I'm not sure if this is relevent but have you seen the comment in the routine 
adjust_arc_center 
(geometry.cpp) which has this comment:-

  // We move the center along a line parallel to the line between
  // the specified start point and end point so that the center
  // is equidistant between the start and end point.
  // It can be proved (using Lagrange multipliers) that this will
  // give the point nearest to the specified center that is equidistant
  // between the start and end point.

This gave me a big headache when trying to make gropdf produce the same arcs as 
grops, until I 
found this comment, since I was using the given centre rather than the adjusted 
centre to draw 
the arc! I don't know how relevant this is to the documentation, I am 
definitely not a maths 
savant, the special school I went to saw little point in giving us an academic 
education.

Cheers 

Deri