Put extension snaps behind an advanced config

This can be backed out when the snapping bevaviour is
considered good enough to be on by default.

common/advanced_config.cpp

@@ -117,6 +117,7 @@ static const wxChar EnableAPILogging[] = wxT( "EnableAPILogging" );
 static const wxChar MaxFileSystemWatchers[] = wxT( "MaxFileSystemWatchers" );
 static const wxChar MinorSchematicGraphSize[] = wxT( "MinorSchematicGraphSize" );
 static const wxChar ResolveTextRecursionDepth[] = wxT( "ResolveTextRecursionDepth" );
+static const wxChar EnableExtensionSnaps[] = wxT( "EnableExtensionSnaps" );
 } // namespace KEYS
 
 
@@ -280,6 +281,8 @@ ADVANCED_CFG::ADVANCED_CFG()
 
     m_ResolveTextRecursionDepth = 3;
 
+    m_EnableExtensionSnaps = false;
+
     loadFromConfigFile();
 }
 
@@ -523,6 +526,10 @@ void ADVANCED_CFG::loadSettings( wxConfigBase& aCfg )
                                                   &m_ResolveTextRecursionDepth,
                                                   m_ResolveTextRecursionDepth, 0, 10 ) );
 
+    configParams.push_back( new PARAM_CFG_BOOL( true, AC_KEYS::EnableExtensionSnaps,
+                                                  &m_EnableExtensionSnaps,
+                                                  m_EnableExtensionSnaps ) );
+
     // Special case for trace mask setting...we just grab them and set them immediately
     // Because we even use wxLogTrace inside of advanced config
     wxString traceMasks;

include/advanced_config.h

@@ -644,6 +644,14 @@ public:
      */
     int m_ResolveTextRecursionDepth;
 
+    /**
+     * Enable snap anchors based on item line extensions.
+     *
+     * Setting name: "EnableExtensionSnaps"
+     * Default value: false
+     */
+    bool m_EnableExtensionSnaps;
+
 ///@}
 
 private:

pcbnew/tools/pcb_grid_helper.cpp

@@ -27,6 +27,7 @@
 
 #include <functional>
 
+#include <advanced_config.h>
 #include <pcb_dimension.h>
 #include <pcb_shape.h>
 #include <footprint.h>
@@ -175,6 +176,12 @@ PCB_GRID_HELPER::~PCB_GRID_HELPER()
 void PCB_GRID_HELPER::AddConstructionItems( std::vector<BOARD_ITEM*> aItems, bool aExtensionOnly,
                                             bool aIsPersistent )
 {
+    if( !ADVANCED_CFG::GetCfg().m_EnableExtensionSnaps )
+    {
+        return;
+    }
+
+
     // For all the elements that get drawn construction geometry,
     // add something suitable to the construction helper.
     // This can be nothing.