Ensure router layer is visible.

Fixes: lp:1663556
* https://bugs.launchpad.net/kicad/+bug/1663556

pcbnew/layer_widget.cpp

@@ -687,6 +687,13 @@ LAYER_NUM LAYER_WIDGET::GetSelectedLayer()
 
 
 void LAYER_WIDGET::SetLayerVisible( LAYER_NUM aLayer, bool isVisible )
+{
+    setLayerCheckbox( aLayer, isVisible );
+    OnLayerVisible( aLayer, isVisible );
+}
+
+
+void LAYER_WIDGET::setLayerCheckbox( LAYER_NUM aLayer, bool isVisible )
 {
     int row = findLayerRow( aLayer );
     if( row >= 0 )

pcbnew/layer_widget.h

@@ -236,6 +236,8 @@ protected:
 
     void insertRenderRow( int aRow, const ROW& aSpec );
 
+    void setLayerCheckbox( LAYER_NUM aLayer, bool isVisible );
+
     /**
      * Function passOnFocus
      * gives away the keyboard focus up to the main parent window.

pcbnew/pcb_edit_frame.h

@@ -623,6 +623,8 @@ public:
      */
     virtual void SetActiveLayer( PCB_LAYER_ID aLayer ) override;
 
+    PCB_LAYER_WIDGET* GetLayerManager() { return m_Layers; }
+
     /**
      * Update the UI to reflect changes to the current layer's transparency.
      */

pcbnew/pcb_layer_widget.cpp

@@ -444,7 +444,7 @@ void PCB_LAYER_WIDGET::SyncLayerVisibilities()
         PCB_LAYER_ID layerId = ToLAYER_ID( getDecodedId( w->GetId() ) );
 
         // this does not fire a UI event
-        SetLayerVisible( layerId, board->IsLayerVisible( layerId ) );
+        setLayerCheckbox( layerId, board->IsLayerVisible( layerId ) );
     }
 }
 
@@ -646,16 +646,19 @@ void PCB_LAYER_WIDGET::OnLayerVisible( int aLayer, bool isVisible, bool isFinal
 
     LSET visibleLayers = brd->GetVisibleLayers();
 
-    visibleLayers.set( aLayer, isVisible );
+    if( visibleLayers.test( aLayer ) != isVisible )
+    {
+        visibleLayers.set( aLayer, isVisible );
 
-    brd->SetVisibleLayers( visibleLayers );
+        brd->SetVisibleLayers( visibleLayers );
 
-    myframe->OnModify();
+        myframe->OnModify();
 
-    EDA_DRAW_PANEL_GAL* galCanvas = myframe->GetGalCanvas();
+        EDA_DRAW_PANEL_GAL* galCanvas = myframe->GetGalCanvas();
 
-    if( galCanvas )
-        galCanvas->GetView()->SetLayerVisible( aLayer, isVisible );
+        if( galCanvas )
+            galCanvas->GetView()->SetLayerVisible( aLayer, isVisible );
+    }
 
     if( isFinal )
         myframe->GetCanvas()->Refresh();

pcbnew/router/router_tool.cpp

@@ -34,6 +34,7 @@ using namespace std::placeholders;
 #include <pcbnew_id.h>
 #include <view/view.h>
 #include <view/view_controls.h>
+#include <pcb_layer_widget.h>
 #include <pcb_painter.h>
 #include <dialogs/dialog_pns_settings.h>
 #include <dialogs/dialog_pns_diff_pair_dimensions.h>
@@ -657,7 +658,8 @@ bool ROUTER_TOOL::prepareInteractive()
 
     frame()->SetActiveLayer( ToLAYER_ID( routingLayer ) );
 
-    // fixme: switch on invisible layer
+    // Force layer visible
+    frame()->GetLayerManager()->SetLayerVisible( routingLayer, true );
 
     // for some reason I don't understand, GetNetclass() may return null sometimes...
     if( m_startItem && m_startItem->Net() >= 0 &&