What is Shader
From wikipedia:
In the field of computer graphics, a shader is a computer program that is used to do shading: the production of appropriate levels of color within an image, or, in the modern era, also to produce special effects or do video post-processing. A definition in layman's terms might be given as "a program that tells a computer how to draw something in a specific and unique way".
通俗地说一段运行在GPU上的代码
shader使用GLSL(OpenGL Shading Language)
渲染管线
