Change Position Relative To to use anchor, not centroid.

Fixes: lp:1793984
* https://bugs.launchpad.net/kicad/+bug/1793984

pcbnew/dialogs/dialog_position_relative.cpp

@@ -192,7 +192,7 @@ void DIALOG_POSITION_RELATIVE::OnOkClick( wxCommandEvent& event )
         POSITION_RELATIVE_TOOL* posrelTool = m_toolMgr->GetTool<POSITION_RELATIVE_TOOL>();
         wxASSERT( posrelTool );
 
-        posrelTool->RelativeItemSelectionMove( m_anchor_position, m_translation, 0.0 );
+        posrelTool->RelativeItemSelectionMove( m_anchor_position, m_translation );
 
         event.Skip();
     }

pcbnew/tools/position_relative_tool.cpp

@@ -102,19 +102,25 @@ int POSITION_RELATIVE_TOOL::PositionRelative( const TOOL_EVENT& aEvent )
 }
 
 
-int POSITION_RELATIVE_TOOL::RelativeItemSelectionMove( wxPoint anchor, wxPoint relativePosition,
-                                                       double rotation )
+int POSITION_RELATIVE_TOOL::RelativeItemSelectionMove( wxPoint aPosAnchor, wxPoint aTranslation )
 {
-    VECTOR2I rp = m_selection.GetCenter();
-    wxPoint rotPoint( rp.x, rp.y );
-    wxPoint translation = anchor + relativePosition - rotPoint;
+    wxPoint aSelAnchor( INT_MAX, INT_MAX );
 
+    // Find top-left item anchor in selection
     for( auto item : m_selection )
     {
-        m_commit->Modify( item );
+        wxPoint itemAnchor = static_cast<BOARD_ITEM*>( item )->GetPosition();
+
+        if( EuclideanNorm( itemAnchor ) < EuclideanNorm( aSelAnchor ) )
+            aSelAnchor = itemAnchor;
+    }
+
+    wxPoint aggregateTranslation = aPosAnchor + aTranslation - aSelAnchor;
 
-        static_cast<BOARD_ITEM*>( item )->Rotate( rotPoint, rotation );
-        static_cast<BOARD_ITEM*>( item )->Move( translation );
+    for( auto item : m_selection )
+    {
+        m_commit->Modify( item );
+        static_cast<BOARD_ITEM*>( item )->Move( aggregateTranslation );
     }
 
     m_commit->Push( _( "Position Relative" ) );

pcbnew/tools/position_relative_tool.h

@@ -62,17 +62,18 @@ public:
     /**
      * Function SelectPositionRelativeItem()
      *
-     * Invokes the picker tool to select the item to which the previos selection will be placed relative to.
+     * Invokes the picker tool to select the item to which the previous selection will be placed
+     * relative to.
      */
     int SelectPositionRelativeItem( const TOOL_EVENT& aEvent  );
 
     /**
      * Function RelativeItemSelectionMove()
      *
-     * Positions the m_position_relative_selection selection relative to anchorpostion using the given translation and rotation.
-     * Rotation is around the center of the selection.
+     * Positions the m_position_relative_selection selection relative to anchorpostion using
+     * the given translation.
      */
-    int RelativeItemSelectionMove( wxPoint anchor, wxPoint translation, double rotation );
+    int RelativeItemSelectionMove( wxPoint anchor, wxPoint translation );
 
     ///> Sets up handlers for various events.
     void setTransitions() override;