BSplineCtrl B样条空间线,在空间绘制可以用鼠任意拖动来改变形状的B样条平滑曲线。用到的知识有：B-Spline ，鼠标三维拾取。-BSplineCtrl B-spline space line drawing in space can be used arbitrarily drag mouse to change the shape of B-spline smoothing curves. The knowledge is used : B-Spline, 3D mouse pi