The viewing frustum has an origin (0,0) at the center of the screen, while screen coordinates have an origin at the upper left of the screen.
The viewing frustum has an origin (0,0) at the center of the screen, while screen coordinates have an origin at the upper left of the screen.
视图锥截体的原点(0,0)在屏幕中心，而屏幕坐标的则在屏幕的左上角。