Fix printing of hidden refs and/or values.

IsLayerVisible() is patched to always return true when printing
(even when "print according to appearance settings" is checked, and
that's too risky to change at this point.  So we also look to see
if the layer colour is set to the background colour.

Fixes #8548

pcbnew/fp_text.cpp

@@ -32,6 +32,7 @@
 #include <settings/settings_manager.h>
 #include <trigo.h>
 #include <kicad_string.h>
+#include <painter.h>
 
 FP_TEXT::FP_TEXT( FOOTPRINT* aParentFootprint, TEXT_TYPE text_type ) :
     BOARD_ITEM( aParentFootprint, PCB_FP_TEXT_T ),
@@ -360,6 +361,8 @@ void FP_TEXT::ViewGetLayers( int aLayers[], int& aCount ) const
 double FP_TEXT::ViewGetLOD( int aLayer, KIGFX::VIEW* aView ) const
 {
     constexpr double HIDE = (double)std::numeric_limits<double>::max();
+    RENDER_SETTINGS* renderSettings = aView->GetPainter()->GetSettings();
+    COLOR4D          backgroundColor = renderSettings->GetLayerColor( LAYER_PCB_BACKGROUND );
 
     if( !aView )
         return 0.0;
@@ -370,13 +373,23 @@ double FP_TEXT::ViewGetLOD( int aLayer, KIGFX::VIEW* aView ) const
         return HIDE;
 
     // Handle Render tab switches
-    if( ( m_Type == TEXT_is_VALUE || GetText() == wxT( "${VALUE}" ) )
-            && !aView->IsLayerVisible( LAYER_MOD_VALUES ) )
+    if( m_Type == TEXT_is_VALUE || GetText() == wxT( "${VALUE}" ) )
+    {
+        if( !aView->IsLayerVisible( LAYER_MOD_VALUES )
+                || renderSettings->GetLayerColor( LAYER_MOD_VALUES ) == backgroundColor )
+        {
             return HIDE;
+        }
+    }
 
-    if( ( m_Type == TEXT_is_REFERENCE || GetText() == wxT( "${REFERENCE}" ) )
-            && !aView->IsLayerVisible( LAYER_MOD_REFERENCES ) )
+    if( m_Type == TEXT_is_REFERENCE || GetText() == wxT( "${REFERENCE}" ) )
+    {
+        if( !aView->IsLayerVisible( LAYER_MOD_REFERENCES )
+                || renderSettings->GetLayerColor( LAYER_MOD_REFERENCES ) == backgroundColor )
+        {
             return HIDE;
+        }
+    }
 
     if( !IsParentFlipped() && !aView->IsLayerVisible( LAYER_MOD_FR ) )
         return HIDE;