WPF中的Drawing

public override void DrawEllipse(Brush brush, Pen pen, Point center, AnimationClock centerAnimations, double radiusX, AnimationClock radiusXAnimations, double radiusY, AnimationClock radiusYAnimations)
    {
        this.VerifyApiNonstructuralChange();
        if ((brush != null) || (pen != null))
        {
            EllipseGeometry newFreezable = new EllipseGeometry(center, radiusX, radiusY) {
                CanBeInheritanceContext = this.CanBeInheritanceContext
            };
            this.SetupNewFreezable(newFreezable, ((centerAnimations == null) && (radiusXAnimations == null)) && (radiusYAnimations == null));
            if (centerAnimations != null)
            {
                newFreezable.ApplyAnimationClock(EllipseGeometry.CenterProperty, centerAnimations);
            }
            if (radiusXAnimations != null)
            {
                newFreezable.ApplyAnimationClock(EllipseGeometry.RadiusXProperty, radiusXAnimations);
            }
            if (radiusYAnimations != null)
            {
                newFreezable.ApplyAnimationClock(EllipseGeometry.RadiusYProperty, radiusYAnimations);
            }
            this.AddNewGeometryDrawing(brush, pen, newFreezable);
        }
    }

private void AddNewGeometryDrawing(Brush brush, Pen pen, Geometry geometry)
{
    GeometryDrawing newFreezable = new GeometryDrawing {
        CanBeInheritanceContext = this.CanBeInheritanceContext,
        Brush = brush,
        Pen = pen,
        Geometry = geometry
    };
    this.SetupNewFreezable(newFreezable, (((brush == null) || brush.IsFrozen) && ((pen == null) || pen.IsFrozen)) && geometry.IsFrozen);
    this.AddDrawing(newFreezable);
}

private void AddDrawing(Drawing newDrawing)
{
    if (this._rootDrawing == null)
    {
        this._rootDrawing = newDrawing;
    }
    else if (this._currentDrawingGroup == null)
    {
        this._currentDrawingGroup = new DrawingGroup();
        this._currentDrawingGroup.CanBeInheritanceContext = this.CanBeInheritanceContext;
        this.SetupNewFreezable(this._currentDrawingGroup, false);
        this._currentDrawingGroup.Children.Add(this._rootDrawing);
        this._currentDrawingGroup.Children.Add(newDrawing);
        this._rootDrawing = this._currentDrawingGroup;
    }
    else
    {
        this._currentDrawingGroup.Children.Add(newDrawing);
    }
}