Fix incorrect arc bounding box calculation.

add comments to SHAPE_ARC ctor.

common/geometry/shape_arc.cpp

@@ -155,9 +155,10 @@ const BOX2I SHAPE_ARC::BBox( int aClearance ) const
 {
     BOX2I bbox;
     std::vector<VECTOR2I> points;
-    points.push_back( m_pc );
+    // Put start and end points in the point list
     points.push_back( m_p0 );
     points.push_back( GetP1() );
+//    points.push_back( m_pc );     the center point is not necessary in the BBox
 
     double start_angle = GetStartAngle();
     double end_angle = start_angle + GetCentralAngle();

gerbview/gerber_draw_item.cpp

@@ -34,6 +34,7 @@
 #include <gerber_file_image.h>
 #include <gerber_file_image_list.h>
 #include <kicad_string.h>
+#include <geometry/shape_arc.h>
 
 GERBER_DRAW_ITEM::GERBER_DRAW_ITEM( GERBER_FILE_IMAGE* aGerberImageFile ) :
     EDA_ITEM( (EDA_ITEM*)NULL, GERBER_DRAW_ITEM_T )
@@ -306,10 +307,23 @@ const EDA_RECT GERBER_DRAW_ITEM::GetBoundingBox() const
 
     case GBR_ARC:
     {
-        // Note: using a larger-than-necessary BB to simplify computation
+        double arc_angle =
-        double radius = GetLineLength( m_Start, m_ArcCentre );
+            atan2( double( m_End.y - m_ArcCentre.y ),  double( m_End.x - m_ArcCentre.x ) )
-        bbox.Move( m_ArcCentre - m_Start );
+            - atan2( double( m_Start.y - m_ArcCentre.y ),  double( m_Start.x - m_ArcCentre.x ) );
-        bbox.Inflate( radius + m_Size.x, radius + m_Size.x );
+
+        arc_angle *= 180.0 / M_PI;
+
+        if( arc_angle < 0.0 )
+            arc_angle += 360.0;
+
+        if( m_End == m_Start )      // Arc with the end point = start point is expected to be a circle
+            arc_angle = 360.0;
+
+        SHAPE_ARC arc( m_ArcCentre, m_Start, arc_angle );
+        BOX2I arc_bbox = arc.BBox( m_Size.x / 2 );  // m_Size.x is the line thickness
+        bbox.SetOrigin( arc_bbox.GetX(), arc_bbox.GetY() );
+        bbox.SetWidth( arc_bbox.GetWidth() );
+        bbox.SetHeight( arc_bbox.GetHeight() );
         break;
     }
 

gerbview/gerbview_painter.cpp

@@ -329,12 +329,24 @@ void GERBVIEW_PAINTER::draw( /*const*/ GERBER_DRAW_ITEM* aItem, int aLayer )
         m_gal->DrawArcSegment( center, radius, startAngle, endAngle, width );
 
 #if 0   // Arc Debugging only
+        m_gal->SetIsFill( false );
+        m_gal->SetIsStroke( true );
         m_gal->SetLineWidth( 5 );
-        m_gal->SetStrokeColor( COLOR4D( 0.0, 1.0, 0.0, 1.0 ) );
+        m_gal->SetStrokeColor( COLOR4D( 0.1, 0.5, 0.0, 0.5 ) );
         m_gal->DrawLine( center, aItem->GetABPosition( arcStart ) );
-        m_gal->SetStrokeColor( COLOR4D( 1.0, 0.0, 0.0, 1.0 ) );
+        m_gal->SetStrokeColor( COLOR4D( 0.6, 0.1, 0.0, 0.5 ) );
         m_gal->DrawLine( center, aItem->GetABPosition( arcEnd ) );
 #endif
+
+#if 0   // Bbox arc Debugging only
+        m_gal->SetIsFill( false );
+        m_gal->SetIsStroke( true );
+        EDA_RECT box = aItem->GetBoundingBox();
+        m_gal->SetLineWidth( 5 );
+        m_gal->SetStrokeColor( COLOR4D(0.9, 0.9, 0, 0.4) );
+        // box coordinates are already in AB position.
+        m_gal->DrawRectangle( box.GetOrigin(), box.GetEnd() );
+#endif
         break;
     }
 

include/geometry/shape_arc.h

@@ -36,6 +36,13 @@ public:
     SHAPE_ARC() :
         SHAPE( SH_ARC ), m_centralAngle( 0.0 ), m_width( 0 ) {};
 
+    /**
+     * SHAPE_ARC ctor.
+     * @param aArcCenter is the arc center
+     * @param aArcStartPoint is the arc start point
+     * @param aCenterAngle is the arc angle in degrees
+     * @param aWidth is the arc line thickness
+     */
     SHAPE_ARC( const VECTOR2I& aArcCenter, const VECTOR2I& aArcStartPoint,
                double aCenterAngle, int aWidth = 0 ) :
         SHAPE( SH_ARC ), m_p0( aArcStartPoint ), m_pc( aArcCenter ), m_centralAngle( aCenterAngle ),