基于webgl实现stl格式3d文件读取与显示，自动调整其大小使其适应显示窗口大小，并自动实现其居中显示，以及实现鼠标操作放大缩小平移-3d stl format based webgl achieve read and display file, automatically adjusts its size to adapt to the size of the display window and automatically achieve its centered, and the realization of the mouse to zoom pan