[dia] Bug 312641 - better handling for degenerated arcs (part 1)

[Hans Breuer <hans src gnome org>]

commit d07b294b9d0dcdc29d8452ff285e190d615f4f30
Author: Hans Breuer <hans breuer org>
Date:   Mon Jun 13 17:11:29 2011 +0200

    Bug 312641 - better handling for degenerated arcs (part 1)
    
    With all three points on a straight line there was some serious
    miscalculation not only leading to abandoned rendering but also
    having a hard time to select the arc again (the distance_from
    method was not taking care for degeneration)

 objects/standard/arc.c |   19 ++++++++++++++++---
 1 files changed, 16 insertions(+), 3 deletions(-)
---
diff --git a/objects/standard/arc.c b/objects/standard/arc.c
index 141f5cc..6c43773 100644
--- a/objects/standard/arc.c
+++ b/objects/standard/arc.c
@@ -193,6 +193,15 @@ in_angle(real angle, real startangle, real endangle)
   return (angle>=startangle) && (angle<=endangle);
 }
 
+/* Degenerated arc is a line */
+static gboolean
+arc_is_line (Arc *arc)
+{
+  if (fabs(arc->curve_distance) <= 0.01)
+    return TRUE;
+  return FALSE;
+}
+
 static real
 arc_distance_from(Arc *arc, Point *point)
 {
@@ -203,6 +212,10 @@ arc_distance_from(Arc *arc, Point *point)
   
   endpoints = &arc->connection.endpoints[0];
 
+  if (arc_is_line (arc))
+    return distance_line_point (&endpoints[0], &endpoints[1],
+                                arc->line_width, point);
+
   from_center = *point;
   point_sub(&from_center, &arc->center);
 
@@ -561,7 +574,7 @@ arc_draw(Arc *arc, DiaRenderer *renderer)
   renderer_ops->set_linecaps(renderer, arc->line_caps);
   
   /* Special case when almost line: */
-  if (fabs(arc->curve_distance) <= 0.01) {
+  if (arc_is_line (arc)) {
           TRACE(printf("drawing like a line\n")); 
     renderer_ops->draw_line_with_arrows(renderer,
 					 &gaptmp[0], &gaptmp[1],
@@ -707,8 +720,8 @@ arc_update_data(Arc *arc)
   lensq = (x2-x1)*(x2-x1) + (y2-y1)*(y2-y1);
   radius = lensq/(8*arc->curve_distance) + arc->curve_distance/2.0;
 
-  if (lensq == 0.0)
-	alpha = 1.0; /* arbitrary, but /not/ 1/0  */
+  if (lensq == 0.0 || arc_is_line (arc))
+    alpha = 1.0; /* arbitrary, but /not/ 1/0  */
   else
     alpha = (radius - arc->curve_distance) / sqrt(lensq);