Allow printing backgrounds prior to foreground

Eeschema shows background fills on a different z-level than the rest of
the symbols/elements.  Print the backgrounds prior to the foregrounds in
order to preserve this view for print output

Fixes https://gitlab.com/kicad/code/kicad/issues/12559

(cherry picked from commit e055302a3c)

eeschema/lib_symbol.cpp

@@ -526,7 +526,7 @@ wxString LIB_SYMBOL::SubReference( int aUnit, bool aAddSeparator )
 }
 
 
-void LIB_SYMBOL::Print( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset,
+void LIB_SYMBOL::PrintBackground( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset,
                         int aUnit, int aConvert, const LIB_SYMBOL_OPTIONS& aOpts )
 {
     /* draw background for filled items using background option
@@ -553,6 +553,12 @@ void LIB_SYMBOL::Print( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset
             }
         }
     }
+}
+
+
+void LIB_SYMBOL::Print( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset, int aUnit,
+                        int aConvert, const LIB_SYMBOL_OPTIONS& aOpts )
+{
 
     for( LIB_ITEM& item : m_drawings )
     {

eeschema/lib_symbol.h

@@ -314,6 +314,17 @@ public:
     void Print( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset,
                 int aMulti, int aConvert, const LIB_SYMBOL_OPTIONS& aOpts );
 
+    /**
+     * Print just the background fills of a symbol
+     *
+     * @param aOffset - Position of symbol.
+     * @param aMulti - unit if multiple units per symbol.
+     * @param aConvert - Symbol conversion (DeMorgan) if available.
+     * @param aOpts - Drawing options
+     */
+    void PrintBackground( const RENDER_SETTINGS *aSettings, const wxPoint &aOffset, int aMulti,
+            int aConvert, const LIB_SYMBOL_OPTIONS &aOpts );
+
     /**
      * Plot lib symbol to plotter.
      * Lib Fields not are plotted here, because this plot function

eeschema/sch_item.h

@@ -285,6 +285,15 @@ public:
      */
     virtual void Print( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset ) = 0;
 
+    /**
+     * Print the (optional) backaground elements if they exist
+     * @param aSettings Print settings
+     * @param aOffset is the drawing offset (usually {0,0} but can be different when moving an
+     *                object).
+     */
+
+    virtual void PrintBackground( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset ) {};
+
     /**
      * Move the item by \a aMoveVector to a new position.
      */

eeschema/sch_screen.cpp

@@ -45,7 +45,9 @@
 
 #include <symbol_library.h>
 #include <connection_graph.h>
+#include <lib_item.h>
 #include <lib_pin.h>
+#include <lib_shape.h>
 #include <sch_symbol.h>
 #include <sch_junction.h>
 #include <sch_line.h>
@@ -815,18 +817,21 @@ void SCH_SCREEN::Print( const RENDER_SETTINGS* aSettings )
     }
 
     /// Sort to ensure plot-order consistency with screen drawing
-    std::sort( other.begin(), other.end(),
+    std::stable_sort( other.begin(), other.end(),
                []( const SCH_ITEM* a, const SCH_ITEM* b )
                {
                     if( a->Type() == b->Type() )
                         return a->GetLayer() > b->GetLayer();
 
-                    return a->Type() > b->Type();
+                    return a->Type() < b->Type();
                } );
 
     for( SCH_ITEM* item : bitmaps )
         item->Print( aSettings, wxPoint( 0, 0 ) );
 
+    for( SCH_ITEM* item : other )
+        item->PrintBackground( aSettings, wxPoint( 0, 0 ) );
+
     for( SCH_ITEM* item : other )
         item->Print( aSettings, wxPoint( 0, 0 ) );
 

eeschema/sch_symbol.cpp

@@ -409,6 +409,19 @@ int SCH_SYMBOL::GetUnitCount() const
 }
 
 
+
+void SCH_SYMBOL::PrintBackground( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset )
+{
+    LIB_SYMBOL_OPTIONS opts;
+    opts.transform = m_transform;
+    opts.draw_visible_fields = false;
+    opts.draw_hidden_fields = false;
+
+    if( m_part )
+        m_part->PrintBackground( aSettings, m_pos + aOffset, m_unit, m_convert, opts );
+}
+
+
 void SCH_SYMBOL::Print( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset )
 {
     LIB_SYMBOL_OPTIONS opts;

eeschema/sch_symbol.h

@@ -488,12 +488,21 @@ public:
     /**
      * Print a symbol.
      *
-     * @param aDC is the device context (can be null).
+     * @param aSettings Render settings controlling output
-     * @param aOffset is the drawing offset (usually wxPoint(0,0), but can be different when
+     * @param aOffset is the drawing offset (usually VECTOR2I(0,0), but can be different when
      *                moving an object)
      */
     void Print( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset ) override;
 
+    /**
+     * Print only the background parts of a symbol (if any)
+     *
+     * @param aSettings Render settings controlling output
+     * @param aOffset is the drawing offset (usually VECTOR2I(0,0), but can be different when
+     *                moving an object)
+     */
+    void PrintBackground( const RENDER_SETTINGS* aSettings, const wxPoint& aOffset ) override;
+
     void SwapData( SCH_ITEM* aItem ) override;
 
     /**

eeschema/symbol_editor/symbol_editor_plotter.cpp

@@ -93,5 +93,7 @@ void SYMBOL_EDIT_FRAME::PrintPage( const RENDER_SETTINGS* aSettings )
     plot_offset.x = pagesize.x / 2;
     plot_offset.y = pagesize.y / 2;
 
+    m_symbol->PrintBackground( aSettings, plot_offset, m_unit, m_convert, LIB_SYMBOL_OPTIONS() );
+
     m_symbol->Print( aSettings, plot_offset, m_unit, m_convert, LIB_SYMBOL_OPTIONS() );
 }