原文
Shaders are the modern way of doing 3D graphics. In a way you could claim that this is a step back as most of the 3D functionality that was provided by the fixed function pipeline and required the developer to only specify configuration parameters (lighting attributes, rotation values, etc) must now be implemented by the developer (via shaders), however, this programmability enables great flexibility and innovation.
理解
Shaders 提供了更高的灵活性， 原本 fixed function pipeline 只需程序员提供例如光照的位置， 旋转的角度， 但是光具体怎么实现照射， 旋转是用矩阵还是四元数，都由 fixed function pipeline(固定管线)决定，
现在， 允许程序员用shader语言自己在图形硬件上实现。
reference from http://ogldev.atspace.co.uk/www/tutorial04/tutorial04.html