实现网页上的折角图片撕开效果，初次打开网页的时候，折角是隐藏的，用鼠标在折角上按住左键可以撕开折角，-Angular images on web pages to achieve the effect of tear, first open the page when the knuckle is hidden, press and hold the button with the mouse on the knuckle knuckle can tear,