【Real Time Rendering 1】
1、RTR是一本导论。官网：http://www.realtimerendering.com。
2、At around 6 fps, a sense of interactivity starts to grow.
An application displaying at 15 fps is certainly real-time; the user focuses on action andreaction.
There is a useful limit, however. From about 72 fps and up, differences in the display rate are effectively undetectable.
3、The plane π is said to divide the space into 2 spaces:
1) a positive half-space, where n · x + d > 0,
2) anegative half-space, where n · x + d < 0.
All other points are said to lie in the plane.
4、(x,y) 垂直于 (-y, x)
