Polygon DRC wrong

[Stephen Ecob]

The attached PCB file causes an invalid DRC warning. The upper six sided polygon is more than 4mil from any other objects, but DRC with a minimum separation down to 3.2 mil complains it is too close.

[Peter Clifton (pcjc2)]

Ok - I see why this is likely happening.

in src/find.c, the one polygon is tested against a series of bloated lines following the outline of the second polygon.

In IsPolygonInPolygon()
We have:
              line.Thickness = 2 * Bloat;

But the test which is called, IsLineInPolygon()

Also adds bloat to the line..

(Although it looks like it adds a bloat which is half the size it should be doing!)

[Peter Clifton (pcjc2)]

iff --git a/src/find.c b/src/find.c
index 5d2e92c..e2517a1 100644
--- a/src/find.c
+++ b/src/find.c
@@ -2743,7 +2743,12 @@ IsPolygonInPolygon (PolygonTypePtr P1, PolygonTypePtr P2)

               line.Point1.X = v->point[0];
               line.Point1.Y = v->point[1];
- line.Thickness = 2 * Bloat;
+ line.Thickness = Bloat;
+ /* Another Bloat is added by IsLineInPolygon, making the correct
+ * 2x Bloat. Ideally we would change it there, but doing so
+ * breaks some other DRC checks which rely on the broken behaviour
+ * in IsLineInPolygon.
+ */
               line.Clearance = 0;
               line.Flags = NoFlags ();
               for (v = v->next; v != &c->head; v = v->next)

[Peter Clifton (pcjc2)]

Fixing IsLineInPolygon (and various other places where we add only half the bloat ammount we should be doing) causes lots of breakage with other DRC checks - particularly those which compute shrink / insufficient overlap.

[Stephen Ecob (silicon-on-inspiration)]

Thank you Peter, that patch fixes the problem!
Unfortunately I seem to have another DRC bug with my current board. I'll upload a separate bug for it.

[Chad Parker (parker-charles)]

Fix committed a long time ago.

[Chad Parker (parker-charles)]

Fix committed to pcb repository in 2011.