osg中的工厂模式(c++)

c++中的工厂模式: http://blog.csdn.net/wuzhekai1985

不过在实际应用中,我们往往不需要使用到上文链接中介绍的那么复杂的继承关系,通常一个普通的类就可以解决问题.

osgearth中也使用到了工厂模式:GeometryFactory,很好的解决了圆形,弧形,椭圆,椭圆弧形,矩形的创建.

namespace osgEarth { namespace Symbology{    using namespace osgEarth;    /**     * Convenience class for building simple tessellated Geometry shapes.     */    class OSGEARTHSYMBOLOGY_EXPORT GeometryFactory    {    public:        /**         * Constructs the factory.         * @param srs The spatial reference in which to create the geometry, or NULL to         *            create simple localized geometry.         */        GeometryFactory( const SpatialReference* srs =0L );        /** dtor */        virtual ~GeometryFactory() { }        /**         * Creates a circle geometry.         * @param center Center point (must be in map SRS if a map was provided in ctor)         * @param radius Circle radius         * @param numSegments Number of circumference segments, or zero to automatically calculate it         * @param geomToUse Use this geometry instead of creating a Polygon.         */        Geometry* createCircle(             const osg::Vec3d& center,            const Distance&   radius,            unsigned          numSegments =0,            Geometry*         geomToUse   =0L) const;        /**         * Creates an arc geometry.         * @param center Center point (must be in map SRS if a map was provided in ctor)         * @param radius Arc radius         * @param start  Starting angle of the arc         * @param end    Ending angle of the arc         * @param numSegments Number of circumference segments, or zero to automatically calculate it         * @param pie    Indicates to create a pie shape rather than an arc.         */        Geometry* createArc(            const osg::Vec3d& center,            const Distance&   radius,            const Angle&      startAngle,            const Angle&      endAngle,            unsigned          numSegments =0,            Geometry*         geomToUse   =0L,            bool              pie = false) const;        /**         * Creates a ellipse geometry.         * @param center Center point (must be in map SRS if a map was provided in ctor)         * @param radiusMajor Major radius (X-axis) length         * @param radiusMinor Minor radius (Y-axis) length         * @param rotationAngle with respect to the X-axis         * @param numSegments Number of circumference segments, or zero to automatically calculate it         * @param geomToUse Use this geometry instead of creating a Polygon.         */        Geometry* createEllipse(            const osg::Vec3d& center,            const Distance&   radiusMajor,            const Distance&   radiusMinor,            const Angle&      rotationAngle,            unsigned          numSegments =0,            Geometry*         geomToUse   =0L) const;        /**         * Creates a ellipse geometry.         * @param center Center point (must be in map SRS if a map was provided in ctor)         * @param radiusMajor Major radius (X-axis) length         * @param radiusMinor Minor radius (Y-axis) length         * @param rotationAngle with respect to the X-axis         * @param start  Starting angle of the arc         * @param end    Ending angle of the arc         * @param numSegments Number of circumference segments, or zero to automatically calculate it         * @param geomToUse Use this geometry instead of creating a Polygon.         * @param pie    Indicates to create a pie shape rather than an arc.         */        Geometry* createEllipticalArc(            const osg::Vec3d& center,            const Distance&   radiusMajor,            const Distance&   radiusMinor,            const Angle&      rotationAngle,            const Angle&      startAngle,            const Angle&      endAngle,            unsigned          numSegments =0,            Geometry*         geomToUse   =0L,            bool              pie = false) const;        /**         * Creates a rectangle geometry         * @param center Center point (must be in map SRS if the map was provided in ctor)         * @param width The width of the rectangle         * @param height The height of the rectangle         */        Geometry* createRectangle(            const osg::Vec3d& center,            const Distance&   width,            const Distance&   height ) const;    protected:        osg::ref_ptr<const SpatialReference> _srs;    };} }