Re: gEDA-user: Strange PCB warning

[Peter Clifton <pcjc2@xxxxxxxxx>]

On Thu, 2009-11-12 at 17:16 +0000, Ineiev wrote:
> Sorry, forgot to scale atan2 result:

Is this patch still needed if the bounding-boxes were correct?

Why does the arc intersection test use the bounding boxes anyway.. is it
just a short-cut to avoid computing a more expensive geometric test in
case the supposed circle intersection was outside the other arc's
bounding box?

Does your patch explicitly allow for the thickness of the drawn arc?



> diff --git a/src/find.c b/src/find.c
> index b24512a..62f5df0 100644
> --- a/src/find.c
> +++ b/src/find.c
> @@ -1327,6 +1327,24 @@ PVTouchesLine (LineTypePtr line)
>    return (False);
>  }
> 
> +static int
> +radius_crosses_arc (float x, float y, ArcTypePtr arc)
> +{
> +  float alpha = atan2 (y - arc->Y, x - arc->X) * 180 / M_PI, start, delta;
> +
> +  start = (float) fmod (arc->StartAngle, 360);
> +  delta = arc->Delta;
> +  if (alpha < 0)
> +    alpha += 360;
> +  if (start < 0)
> +    start += 360;
> +  if (delta < 0)
> +    {
> +      start += delta;
> +      delta = -delta;
> +    }
> +  return (start < alpha && start + delta > alpha);
> +}
>  /* ---------------------------------------------------------------------------
>   * check if two arcs intersect
>   * first we check for circle intersections,
> @@ -1424,7 +1442,9 @@ ArcArcIntersect (ArcTypePtr Arc1, ArcTypePtr Arc2)
>        && x + dy >= Arc2->BoundingBox.X1
>        && x + dy <= Arc2->BoundingBox.X2
>        && y - dx >= Arc2->BoundingBox.Y1 && y - dx <= Arc2->BoundingBox.Y2)
> -    return (True);
> +    if (radius_crosses_arc (x + dy, y - dx, Arc1)
> +	&& radius_crosses_arc (x + dy, y - dx, Arc2))
> +      return (True);
> 
>    if (x - dy >= Arc1->BoundingBox.X1
>        && x - dy <= Arc1->BoundingBox.X2
> @@ -1433,7 +1453,9 @@ ArcArcIntersect (ArcTypePtr Arc1, ArcTypePtr Arc2)
>        && x - dy >= Arc2->BoundingBox.X1
>        && x - dy <= Arc2->BoundingBox.X2
>        && y + dx >= Arc2->BoundingBox.Y1 && y + dx <= Arc2->BoundingBox.Y2)
> -    return (True);
> +    if (radius_crosses_arc (x - dy, y + dx, Arc1)
> +	&& radius_crosses_arc (x - dy, y + dx, Arc2))
> +      return (True);
> 
>    /* try the end points in case the ends don't actually pierce the
> outer radii */
>    box = GetArcEnds (Arc1);
> 
> 
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