添加颜色: 作为第二课的扩展，我将叫你如何使用颜色。你将理解两种着色模式，在左图中，三角形用的是光滑着色，四边形用的是平面着色。 -Add color: as the second extension of class, I will tell you how to use color. You will understand the two kinds of color modes, in the left, with a smooth colored triangle, qua