class CORE_EXPORT QgsVectorOverlay
{
%TypeHeaderCode
#include "qgsvectoroverlay.h"
%End
  public:
    QgsVectorOverlay( QgsVectorLayer* vl );
    virtual ~QgsVectorOverlay();

    /**Create the overlay objects contained in a view extent. Subclasses need to implement this method and assign                   width/height information to the overlay ovbjects*/

    virtual void createOverlayObjects( const QgsRenderContext& renderContext ) = 0;

    /**Remove the overlay objects and release their memory*/
    void removeOverlayObjects();

    /**Draw the overlay objects*/
    virtual void drawOverlayObjects( QgsRenderContext& context ) const = 0;

    /**Gives direct access to oberlay objects*/
    QMap<int, QgsOverlayObject*>* overlayObjects() {return &mOverlayObjects;}

    /**Describes the overlay type (e.g. "diagram" or "label")*/
    virtual QString typeName() const = 0;

    /**Set attribute indices necessary to fetch*/
    void setAttributes( const QgsAttributeList& list ) {mAttributes = list;}

    bool displayFlag() const {return mDisplayFlag;}

    /**Display yes/no*/
    void setDisplayFlag( bool flag ) {mDisplayFlag = flag;}

    /**Restore from project file*/
    virtual bool readXML( const QDomNode& overlayNode ) = 0;

    /**Save to project file*/
    virtual bool writeXML( QDomNode& layer_node, QDomDocument& doc ) const = 0;

  protected:
    /**Pointer to the vector layer for this overlay*/
    QgsVectorLayer* mVectorLayer;

    /**True if overlay should be displayed*/
    bool mDisplayFlag;

    /**A list with attribute indexes that are needed for overlay rendering*/
    QgsAttributeList mAttributes;

    /**Key: feature ids, value: the corresponding overlay objects. Normally, they are created for each redraw and deleted before the next redraw*/
    QMap<int, QgsOverlayObject*> mOverlayObjects;

    /**Position constraints that may be set to be persistent after redraws. Key is the feature id, value the map point
        where the feature should be placed*/
    QMap<int, QgsPoint> mPositionConstraints;
};