From cc5c5010f00d48f761c6b5098739efa948c85870 Mon Sep 17 00:00:00 2001
From: Jon Evans <jon@craftyjon.com>
Date: Sun, 17 Sep 2017 21:03:58 -0400
Subject: [PATCH] Fix some layer visibility behavior

---
 gerbview/class_gerbview_layer_widget.cpp |  4 ++--
 gerbview/gerbview_frame.cpp              | 18 +++++++++++++++++-
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/gerbview/class_gerbview_layer_widget.cpp b/gerbview/class_gerbview_layer_widget.cpp
index f5ef8b9b10..6e9b8e312f 100644
--- a/gerbview/class_gerbview_layer_widget.cpp
+++ b/gerbview/class_gerbview_layer_widget.cpp
@@ -305,9 +305,9 @@ void GERBER_LAYER_WIDGET::OnLayerVisible( int aLayer, bool isVisible, bool isFin
     long visibleLayers = myframe->GetVisibleLayers();
 
     if( isVisible )
-        visibleLayers |= 1 << aLayer;
+        visibleLayers |= 1 << ( aLayer - GERBVIEW_LAYER_ID_START );
     else
-        visibleLayers &= ~( 1 << aLayer );
+        visibleLayers &= ~( 1 << ( aLayer - GERBVIEW_LAYER_ID_START ) );
 
     myframe->SetVisibleLayers( visibleLayers );
 
diff --git a/gerbview/gerbview_frame.cpp b/gerbview/gerbview_frame.cpp
index 9f15392670..a4123a433a 100644
--- a/gerbview/gerbview_frame.cpp
+++ b/gerbview/gerbview_frame.cpp
@@ -677,7 +677,23 @@ bool GERBVIEW_FRAME::IsElementVisible( GERBVIEW_LAYER_ID aItemIdVisible ) const
 
 long GERBVIEW_FRAME::GetVisibleLayers() const
 {
-    return -1;    // TODO
+    long layerMask = 0;
+
+    if( auto canvas = GetGalCanvas() )
+    {
+        // NOTE: This assumes max 32 drawlayers!
+        for( int i = 0; i < GERBER_DRAWLAYERS_COUNT; i++ )
+        {
+            if( canvas->GetView()->IsLayerVisible( GERBER_DRAW_LAYER( i ) ) )
+                layerMask |= ( 1 << i );
+        }
+
+        return layerMask;
+    }
+    else
+    {
+        return -1;
+    }
 }