GRID_HELPER: Finish drawing closed path

When we draw a path, we usually want to close the path when clicking on
the end of another line.  This uses grid helper to ensure this
progression happens as expected.

pcbnew/tools/drawing_tool.cpp

@@ -1105,27 +1105,47 @@ bool DRAWING_TOOL::drawSegment( int aShape, DRAWSEGMENT*& aGraphic,
             }
             else
             {
+                auto snapItem = dyn_cast<DRAWSEGMENT*>( grid.GetSnapped() );
+                auto mod = dyn_cast<MODULE*>( m_frame->GetModel() );
+
                 if( aGraphic->GetEnd() == aGraphic->GetStart()
-                    || ( evt->IsDblClick( BUT_LEFT ) && aShape == S_SEGMENT ) )
+                    || ( evt->IsDblClick( BUT_LEFT ) && aShape == S_SEGMENT )
+                    || snapItem )
                 // User has clicked twice in the same spot
+                //  or clicked on the end of an existing segment (closing a path)
                 {
+                    BOARD_COMMIT commit( m_frame );
+
                     // a clear sign that the current drawing is finished
                     // Now we have to add the helper line as well, unless it is zero-length
-                    if( direction45 && line45.GetStart() != aGraphic->GetStart() )
+                    if( direction45  && line45.GetStart() != aGraphic->GetStart() )
                     {
-                        BOARD_ITEM_CONTAINER* parent = m_frame->GetModel();
-                        DRAWSEGMENT* l = m_editModules ? new EDGE_MODULE( (MODULE*) parent )
-                                         : new DRAWSEGMENT;
+                        DRAWSEGMENT* l = m_editModules ? new EDGE_MODULE( mod ) : new DRAWSEGMENT;
 
                         // Copy coordinates, layer, etc.
-                        *static_cast<DRAWSEGMENT*>( l ) = line45;
+                        *l = line45;
+
+                        // If snapping, add both paths
+                        if( snapItem && l->GetLength() > 0.0 )
+                            commit.Add( l->Clone() );
+
                         l->SetEnd( aGraphic->GetStart() );
+                        commit.Add( l );
+                    }
 
-                        BOARD_COMMIT commit( m_frame );
+                    // If the user clicks on an existing snap point from a drawsegment
+                    //  we finish the segment as they are likely closing a path
+                    else if( snapItem && aGraphic->GetLength() > 0.0 )
+                    {
+                        DRAWSEGMENT* l = m_editModules ? new EDGE_MODULE( mod ) : new DRAWSEGMENT;
+
+                        *l = *aGraphic;
                         commit.Add( l );
-                        commit.Push( _( "Draw a line" ) );
                     }
 
+                    if( !commit.Empty() )
+                        commit.Push( _( "Draw a line" ) );
+
                     delete aGraphic;
                     aGraphic = NULL;
                 }

pcbnew/tools/grid_helper.cpp

@@ -304,15 +304,26 @@ VECTOR2I GRID_HELPER::BestSnapAnchor( const VECTOR2I& aOrigin, const LSET& aLaye
             else
                 m_frame->GetGalCanvas()->GetView()->SetVisible( &m_viewSnapPoint, true );
 
+            m_snapItem = nearest;
             return nearest->pos;
         }
     }
 
+    m_snapItem = nullptr;
     m_frame->GetGalCanvas()->GetView()->SetVisible( &m_viewSnapPoint, false );
     return nearestGrid;
 }
 
 
+BOARD_ITEM* GRID_HELPER::GetSnapped( void ) const
+{
+    if( !m_snapItem )
+        return nullptr;
+
+    return m_snapItem->item;
+}
+
+
 void GRID_HELPER::computeAnchors( BOARD_ITEM* aItem, const VECTOR2I& aRefPos )
 {
     VECTOR2I origin;

pcbnew/tools/grid_helper.h

@@ -49,6 +49,15 @@ public:
     VECTOR2I GetGrid() const;
     VECTOR2I GetOrigin() const;
 
+    /**
+     * Function GetSnapped
+     * If the GRID_HELPER has highlighted a snap point (target shown), this function
+     * will return a pointer to the item to which it snapped.
+     *
+     * @return NULL if not snapped.  Pointer to snapped item otherwise
+     */
+    BOARD_ITEM* GetSnapped() const;
+
     void SetAuxAxes( bool aEnable, const VECTOR2I& aOrigin = VECTOR2I( 0, 0 ), bool aEnableDiagonal = false );
 
     VECTOR2I Align( const VECTOR2I& aPoint ) const;
@@ -119,6 +128,7 @@ private:
     bool m_enableSnap;              ///< If true, allow snapping to other items on the layers
     bool m_enableGrid;              ///< If true, allow snapping to grid
     int m_snapSize;                 ///< Sets the radius in screen units for snapping to items
+    ANCHOR* m_snapItem;             ///< Pointer to the currently snapped item in m_anchors (NULL if not snapped)
 
     KIGFX::ORIGIN_VIEWITEM m_viewSnapPoint;
     KIGFX::ORIGIN_VIEWITEM m_viewAxis;