说明：  OpenGL着色语言（GLSL――OpenGL Shading Language）是用来在OpenGL中着色编程的语言，也即开发人员写的短小的自定义程序，他们是在图形卡的GPU （Graphic Processor Unit图形处理单元）上执行的，代替了固定的渲染管线的一部分
(The recent trend in graphics hardware has been to replace fixed functionality with programmability in areas that have grown exceedingly complex (e.g., vertex processing and fragment processing). The OpenGL Shading Language has been designed to allow application programmers to express the processing that occurs at those programmable points of the OpenGL pipeline. Independently compilable units that are written in this language are called shaders. A program is a set of shaders that are compiled and linked together)