PCB_SHAPE::GetFocusPosition(): returns a point on the outline instead of center.

This function is used in DRC to locate a graphic shape. For not filled shapes,
this point must be on the shape outline, not on the center of the shape (the center
shows nothing)
Fixes #8832
https://gitlab.com/kicad/code/kicad/issues/8832

pcbnew/pcb_shape.cpp

@@ -76,6 +76,47 @@ wxPoint PCB_SHAPE::GetPosition() const
 }
 
 
+const wxPoint PCB_SHAPE::GetFocusPosition() const
+{
+    // For some shapes return the visual center, but for not filled polygonal shapes,
+    // the center is usually far from the shape: a point on the outline is better
+
+    switch( m_shape )
+    {
+    case SHAPE_T::CIRCLE:
+        if( !IsFilled() )
+            return wxPoint( GetCenter().x + GetRadius(), GetCenter().y );
+        break;
+
+    case SHAPE_T::RECT:
+        if( !IsFilled() )
+            return GetStart();
+        break;
+
+    case SHAPE_T::POLY:
+        if( !IsFilled() )
+        {
+            VECTOR2I pos = GetPolyShape().Outline(0).CPoint(0);
+            return wxPoint( pos.x, pos.y );
+        }
+        break;
+
+    case SHAPE_T::ARC:
+        return GetArcMid();
+        break;
+
+    case SHAPE_T::BEZIER:
+        return GetStart();
+        break;
+
+    default:
+        break;
+    }
+
+    return GetCenter();
+}
+
+
 double PCB_SHAPE::GetLength() const
 {
     double length = 0.0;

pcbnew/pcb_shape.h

@@ -205,10 +205,12 @@ public:
      */
     void SetArcGeometry( const wxPoint& aStart, const wxPoint& aMid, const wxPoint& aEnd );
 
-    const wxPoint GetFocusPosition() const override
-    {
-        return GetCenter();
-    }
+    /**
+     * Allows items to return their visual center rather than their anchor.
+     * For some shapes this is similar to GetPosition, but for polygonal shapes,
+     * the anchor is not suitable (shows nothing): a point on the outline is better
+     */
+    const wxPoint GetFocusPosition() const override;
 
     /**
      * Return the parent footprint or NULL if PCB_SHAPE does not belong to a footprint.