eeschema: Find the closest line end to the mouse when grabbing

Fixes: lp:1842175
* https://bugs.launchpad.net/kicad/+bug/1842175

eeschema/onrightclick.cpp

@@ -150,7 +150,15 @@ bool SCH_EDIT_FRAME::OnRightClick( const wxPoint& aPosition, wxMenu* PopMenu )
             return false;
 
         if( item )
-            SetCrossHairPosition( item->GetPosition(), false );
+        {
+            SCH_LINE* line = dynamic_cast<SCH_LINE*>( item );
+
+            // The schematic lines have two possible points to use
+            if( line )
+                SetCrossHairPosition( line->GetClosestPoint( aPosition ), false );
+            else
+                SetCrossHairPosition( item->GetPosition(), false );
+        }
     }
 
     // If a command is in progress: add "cancel" and "end tool" menu

eeschema/sch_line.cpp

@@ -30,6 +30,7 @@
 #include <fctsys.h>
 #include <gr_basic.h>
 #include <macros.h>
+#include <trigo.h>
 #include <sch_draw_panel.h>
 #include <plotter.h>
 #include <base_units.h>
@@ -299,7 +300,7 @@ int SCH_LINE::GetPenSize() const
 {
     if( m_size > 0 )
         return m_size;
-    
+
     return GetDefaultWidth();
 }
 
@@ -487,6 +488,19 @@ EDA_ITEM* SCH_LINE::MergeOverlap( SCH_LINE* aLine )
 }
 
 
+wxPoint SCH_LINE::GetClosestPoint( const wxPoint& aPoint )
+{
+    // Compute the euclidean distance between the reference and the ends
+    double startDis  = GetLineLength( aPoint, m_start );
+    double endDis    = GetLineLength( aPoint, m_end );
+
+    if( startDis < endDis )
+        return m_start;
+    else
+        return m_end;
+}
+
+
 void SCH_LINE::GetEndPoints( std::vector <DANGLING_END_ITEM>& aItemList )
 {
     if( GetLayer() == LAYER_NOTES )

eeschema/sch_line.h

@@ -81,6 +81,15 @@ public:
 
     void SetEndPoint( const wxPoint& aPosition ) { m_end = aPosition; }
 
+    /**
+     * Find the end point of the line (either start or end) that is closest
+     * to the provided point.
+     *
+     * @param aPoint the point to compare against
+     * @return The coordinates of the closest end point
+     */
+    wxPoint GetClosestPoint( const wxPoint& aPoint );
+
     int GetDefaultStyle() const;
 
     void SetLineStyle( const int aStyle );