class SPPaintServer : public SPObject {
public:
    SPPaintServer();
    virtual ~SPPaintServer();

    bool isSwatch() const;
    bool isSolid() const;
    virtual bool isValid() const;

protected:
    bool swatch;
};

class SPPattern : public SPPaintServer {
public:
    gdouble get_x(bool chain=true);
    gdouble get_y(bool chain=true);
    gdouble get_width(bool chain=true);
    gdouble get_heigth(bool chain=true);
    Geom::OptRect get_view_box(bool chain=true);
    //similar for pattern_units, pattern_content_unit, pattern_transform
}

class NRPaintServer {
public:
    static NRPaintServer* create(SPPaintServer* ps) //can also use boost::unique_pointer<NRPaintServer>

    virtual cairo_pattern_t* pattern_new(cairo_t *ct, Geom::OptRect const &bbox, double opacity) = 0;
}

class NRPattern : public NRPaintServer {
public:
    NRPattern(SPPattern& p);

    cairo_pattern_t* pattern_new(cairo_t *ct, Geom::OptRect const &bbox, double opacity) {
        //use _pattern and render the pattern
    }
private:
    SPPattern& _pattern;
}

/****************************
  Class using NRPaintServer - NRStyle
*****************************/
class NRStyle {
//...
    bool prepareFill() {
        NRPaintServer* ps = NRPaintServer::create(fill.server);
        fill_pattern = ps->pattern_new(dc.raw(), paintbox, fill.opacity);
        delete ps;
        //or store it somewhere for performance reasons
    }
}