Work around a round-off bug in Clipper.

Fixes https://gitlab.com/kicad/code/kicad/issues/6260

libs/kimath/src/geometry/shape_poly_set.cpp

@@ -604,6 +604,10 @@ void SHAPE_POLY_SET::Inflate( int aAmount, int aCircleSegmentsCount,
     if( aCircleSegmentsCount < 6 ) // avoid incorrect aCircleSegmentsCount values
         aCircleSegmentsCount = 6;
 
+    // Clipper has a bug where round-off error is accumulated into the last segment.  Increasing
+    // the segment count by one probably accounts for this, but we increment by 2 to be safe.
+    aCircleSegmentsCount += 2;
+
     double coeff;
 
     if( aCircleSegmentsCount > SEG_CNT_MAX || arc_tolerance_factor[aCircleSegmentsCount] == 0 )

pcbnew/board_items_to_polygon_shape_transform.cpp

@@ -627,7 +627,11 @@ void D_PAD::TransformShapeWithClearanceToPolygon( SHAPE_POLY_SET& aCornerBuffer,
         {
             int numSegs = std::max( GetArcToSegmentCount( aClearanceValue, aError, 360.0 ),
                                     pad_min_seg_per_circle_count );
-            int clearance = aClearanceValue + GetCircleToPolyCorrection( aError );
+            int clearance = aClearanceValue;
+
+            if( aErrorLoc == ERROR_OUTSIDE )
+                clearance += GetCircleToPolyCorrection( aError );
+
             outline.Inflate( clearance, numSegs );
         }
 

pcbnew/zone_filler.cpp

@@ -753,6 +753,8 @@ void ZONE_FILLER::buildCopperItemClearances( const ZONE_CONTAINER* aZone, PCB_LA
                     else
                         gap = evalRulesForItems( CLEARANCE_CONSTRAINT, aZone, aPad, aLayer );
 
+                    gap += extra_margin;
+
                     addKnockout( aPad, aLayer, gap, aHoles );
                 }
             };