arrows when two points are on each other

[Trevor Spiteri <tbspit eng um edu mt>]

When there are two (or more) points at the end and there is an arrow
at that end, the arrow is always pointing right. This may be a
non-issue for polylines (just remove the redundant points).
However, for a zig-zag line sometimes this is a need.

So I put this function in lib/arrows.c:

Point *
next_point(Point *points, int rem)
{
  Point *endpoint;
  int dir;

  endpoint = points;      /* the real endpoint */
  dir = rem > 0 ? 1 : -1; /* direction (+ve / -ve) */

  while (rem != 0) {      /* keep in legal range */
    /* compare next point to the end point, and if they are different, */
    /* return the differing point */
    points += dir;
    if (endpoint->x != points->x || endpoint->y != points->y)
      return points;

    /* one less point to use */
    rem -= dir;
  }

  /* no different points were found */
  return points;
}

This function moves forwards or backwards from "points" (according
to "dir") to a point which is not coincident with it. It can move to a
maximum offset "rem" from the original pointer.

I also put the prototype in lib/arrows.h and modified the following lines
in objects/standard/zigzagline.c (diff for 0.88.1).
219c219
<            &points[0], &points[1],
---
 >            &points[0], next_point(&points[0], n-1),
226c226
<            &points[n-1], &points[n-2],
---
 >            &points[n-1], next_point(&points[n-1], 1-n),

I did something similar to objects/standard/polyline.c.

Sorry if I am posting this to the wrong list, I don't know how these
lists work very well.

Thanks
Trevor Spiteri