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

eeschema/lib_symbol.cpp

@@ -619,8 +619,8 @@ wxString LIB_SYMBOL::SubReference( int aUnit, bool aAddSeparator )
 }
 
 
-void LIB_SYMBOL::Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset, int aUnit,
-                        int aConvert, const LIB_SYMBOL_OPTIONS& aOpts, bool aDimmed )
+void LIB_SYMBOL::PrintBackground( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset,
+                        int aUnit, int aConvert, const LIB_SYMBOL_OPTIONS& aOpts, bool aDimmed )
 {
     /* draw background for filled items using background option
      * Solid lines will be drawn after the background
@@ -650,6 +650,12 @@ void LIB_SYMBOL::Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffse
             }
         }
     }
+}
+
+
+void LIB_SYMBOL::Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset, int aUnit,
+                        int aConvert, const LIB_SYMBOL_OPTIONS& aOpts, bool aDimmed )
+{
 
     for( LIB_ITEM& item : m_drawings )
     {

eeschema/lib_symbol.h

@@ -327,6 +327,18 @@ public:
     void Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset, int aMulti, int aConvert,
                 const LIB_SYMBOL_OPTIONS& aOpts, bool aDimmed );
 
+    /**
+     * 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
+     * @param aDimmed - Reduce brightness of symbol
+     */
+    void PrintBackground( const RENDER_SETTINGS *aSettings, const VECTOR2I &aOffset, int aMulti,
+            int aConvert, const LIB_SYMBOL_OPTIONS &aOpts, bool aDimmed );
+
     /**
      * Plot lib symbol to plotter.
      * Lib Fields not are plotted here, because this plot function

eeschema/sch_item.h

@@ -276,6 +276,15 @@ public:
      */
     virtual void Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& 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 VECTOR2I& aOffset ) {};
+
     /**
      * Move the item by \a aMoveVector to a new position.
      */

eeschema/sch_screen.cpp

@@ -39,7 +39,9 @@
 
 #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>
@@ -1046,18 +1048,21 @@ 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, VECTOR2I( 0, 0 ) );
 
+    for( SCH_ITEM* item : other )
+        item->PrintBackground( aSettings, VECTOR2I( 0, 0 ) );
+
     for( SCH_ITEM* item : other )
         item->Print( aSettings, VECTOR2I( 0, 0 ) );
 

eeschema/sch_shape.cpp

@@ -241,14 +241,11 @@ int SCH_SHAPE::GetPenWidth() const
 }
 
 
-void SCH_SHAPE::Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset )
+void SCH_SHAPE::PrintBackground( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset )
 {
-    int      penWidth = GetPenWidth();
     wxDC*    DC = aSettings->GetPrintDC();
     COLOR4D  color;
 
-    penWidth = std::max( penWidth, aSettings->GetMinPenWidth() );
-
     unsigned ptCount = 0;
     VECTOR2I* buffer = nullptr;
 
@@ -305,6 +302,39 @@ void SCH_SHAPE::Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset
         }
     }
 
+}
+
+
+void SCH_SHAPE::Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset )
+{
+    int      penWidth = GetPenWidth();
+    wxDC*    DC = aSettings->GetPrintDC();
+    COLOR4D  color;
+
+    penWidth = std::max( penWidth, aSettings->GetMinPenWidth() );
+
+    unsigned ptCount = 0;
+    VECTOR2I* buffer = nullptr;
+
+    if( GetShape() == SHAPE_T::POLY )
+    {
+        SHAPE_LINE_CHAIN poly = m_poly.Outline( 0 );
+
+        ptCount = poly.GetPointCount();
+        buffer = new VECTOR2I[ptCount];
+
+        for( unsigned ii = 0; ii < ptCount; ++ii )
+            buffer[ii] = poly.CPoint( ii );
+    }
+    else if( GetShape() == SHAPE_T::BEZIER )
+    {
+        ptCount = m_bezierPoints.size();
+        buffer = new VECTOR2I[ptCount];
+
+        for( size_t ii = 0; ii < ptCount; ++ii )
+            buffer[ii] = m_bezierPoints[ii];
+    }
+
     if( GetStroke().GetColor() == COLOR4D::UNSPECIFIED )
         color = aSettings->GetLayerColor( LAYER_NOTES );
     else

eeschema/sch_shape.h

@@ -113,6 +113,7 @@ public:
 
 private:
     void Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset ) override;
+    void PrintBackground( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset ) override;
 
     EDA_ANGLE getParentOrientation() const override { return ANGLE_0; }
     VECTOR2I getParentPosition() const override { return VECTOR2I(); }

eeschema/sch_symbol.cpp

@@ -451,6 +451,18 @@ bool SCH_SYMBOL::HasUnitDisplayName( int aUnit )
 }
 
 
+void SCH_SYMBOL::PrintBackground( const RENDER_SETTINGS* aSettings, const VECTOR2I& 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, GetDNP() );
+}
+
+
 void SCH_SYMBOL::Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& aOffset )
 {
     LIB_SYMBOL_OPTIONS opts;

eeschema/sch_symbol.h

@@ -539,12 +539,21 @@ 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 VECTOR2I(0,0), but can be different when
      *                moving an object)
      */
     void Print( const RENDER_SETTINGS* aSettings, const VECTOR2I& 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 VECTOR2I& aOffset ) override;
+
     void SwapData( SCH_ITEM* aItem ) override;
 
     /**

eeschema/symbol_editor/symbol_editor_plotter.cpp

@@ -99,5 +99,7 @@ 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(), false );
+
     m_symbol->Print( aSettings, plot_offset, m_unit, m_convert, LIB_SYMBOL_OPTIONS(), false );
 }