Add support for reversed draw order and Cairo negative draw mode

common/draw_panel_gal.cpp

@@ -391,7 +391,11 @@ bool EDA_DRAW_PANEL_GAL::SwitchBackend( GAL_TYPE aGalType )
         m_painter->SetGAL( m_gal );
 
     if( m_view )
+    {
         m_view->SetGAL( m_gal );
+        // Note: OpenGL requires reverse draw order when draw priority is enabled
+        m_view->ReverseDrawOrder( aGalType == GAL_TYPE_OPENGL );
+    }
 
     m_backend = aGalType;
 

common/gal/cairo/cairo_gal.cpp

@@ -857,6 +857,12 @@ void CAIRO_GAL::ClearTarget( RENDER_TARGET aTarget )
 }
 
 
+void CAIRO_GAL::SetNegativeDrawMode( bool aSetting )
+{
+    cairo_set_operator( currentContext, aSetting ? CAIRO_OPERATOR_CLEAR : CAIRO_OPERATOR_OVER );
+}
+
+
 void CAIRO_GAL::DrawCursor( const VECTOR2D& aCursorPosition )
 {
     cursorPosition = aCursorPosition;

common/view/view.cpp

@@ -267,7 +267,8 @@ VIEW::VIEW( bool aIsDynamic ) :
     m_gal( NULL ),
     m_dynamic( aIsDynamic ),
     m_useDrawPriority( false ),
-    m_nextDrawPriority( 0 )
+    m_nextDrawPriority( 0 ),
+    m_reverseDrawOrder( false )
 {
     m_boundary.SetMaximum();
     m_allItems.reserve( 32768 );
@@ -815,8 +816,10 @@ void VIEW::UpdateAllLayersOrder()
 
 struct VIEW::drawItem
 {
-    drawItem( VIEW* aView, int aLayer, bool aUseDrawPriority ) :
+    drawItem( VIEW* aView, int aLayer, bool aUseDrawPriority, bool aReverseDrawOrder ) :
-        view( aView ), layer( aLayer ), useDrawPriority( aUseDrawPriority )
+        view( aView ), layer( aLayer ),
+        useDrawPriority( aUseDrawPriority ),
+        reverseDrawOrder( aReverseDrawOrder )
     {
     }
 
@@ -840,10 +843,16 @@ struct VIEW::drawItem
 
     void deferredDraw()
     {
+        if( reverseDrawOrder )
             std::sort( drawItems.begin(), drawItems.end(),
                        []( VIEW_ITEM* a, VIEW_ITEM* b ) -> bool {
                            return b->viewPrivData()->m_drawPriority < a->viewPrivData()->m_drawPriority;
                        });
+        else
+            std::sort( drawItems.begin(), drawItems.end(),
+                       []( VIEW_ITEM* a, VIEW_ITEM* b ) -> bool {
+                           return a->viewPrivData()->m_drawPriority < b->viewPrivData()->m_drawPriority;
+                       });
 
         for( auto item : drawItems )
             view->draw( item, layer );
@@ -851,7 +860,7 @@ struct VIEW::drawItem
 
     VIEW* view;
     int layer, layers[VIEW_MAX_LAYERS];
-    bool useDrawPriority;
+    bool useDrawPriority, reverseDrawOrder;
     std::vector<VIEW_ITEM*> drawItems;
 };
 
@@ -862,7 +871,7 @@ void VIEW::redrawRect( const BOX2I& aRect )
     {
         if( l->visible && IsTargetDirty( l->target ) && areRequiredLayersEnabled( l->id ) )
         {
-            drawItem drawFunc( this, l->id, m_useDrawPriority );
+            drawItem drawFunc( this, l->id, m_useDrawPriority, m_reverseDrawOrder );
 
             m_gal->SetTarget( l->target );
             m_gal->SetLayerDepth( l->renderingOrder );

include/gal/cairo/cairo_gal.h

@@ -240,6 +240,9 @@ public:
     /// @copydoc GAL::ClearTarget()
     virtual void ClearTarget( RENDER_TARGET aTarget ) override;
 
+    /// @copydoc GAL::SetNegativeDrawMode()
+    virtual void SetNegativeDrawMode( bool aSetting ) override;
+
     // -------
     // Cursor
     // -------

include/gal/graphics_abstraction_layer.h

@@ -772,6 +772,19 @@ public:
      */
     virtual void ClearTarget( RENDER_TARGET aTarget ) {};
 
+    /**
+     * @brief Sets negative draw mode in the renderer
+     *
+     * When negative mode is enabled, drawn items will subtract from
+     * previously drawn items.  This is mainly needed for Gerber
+     * negative item support in Cairo, since unlike in OpenGL, objects
+     * drawn with zero opacity on top of other objects would not normally
+     * mask objects in Cairo.  This method is a no-op in OpenGL.
+     *
+     * @param aSetting is true if negative mode should be enabled
+     */
+    virtual void SetNegativeDrawMode( bool aSetting ) {};
+
     // -------------
     // Grid methods
     // -------------

include/gal/opengl/opengl_gal.h

@@ -239,6 +239,9 @@ public:
     /// @copydoc GAL::ClearTarget()
     virtual void ClearTarget( RENDER_TARGET aTarget ) override;
 
+    /// @copydoc GAL::SetNegativeDrawMode()
+    virtual void SetNegativeDrawMode( bool aSetting ) override {}
+
     // -------
     // Cursor
     // -------

include/view/view.h

@@ -630,6 +630,25 @@ public:
         m_useDrawPriority = aFlag;
     }
 
+    /**
+     * Function IsDrawOrderReversed()
+     * @return true if draw order is reversed
+     */
+    bool IsDrawOrderReversed() const
+    {
+        return m_reverseDrawOrder;
+    }
+
+    /**
+     * Function ReverseDrawOrder()
+     * Only takes effect if UseDrawPriority is true.
+     * @param aFlag is true if draw order should be reversed
+     */
+    void ReverseDrawOrder( bool aFlag )
+    {
+        m_reverseDrawOrder = aFlag;
+    }
+
     static const int VIEW_MAX_LAYERS = 512;      ///< maximum number of layers that may be shown
 
 
@@ -796,6 +815,9 @@ private:
 
     /// The next sequential drawing priority
     int m_nextDrawPriority;
+
+    /// Flag to reverse the draw order when using draw priority
+    bool m_reverseDrawOrder;
 };
 } // namespace KIGFX