译自《OpenGL® Shading Language, Second Edition》
本章主要回顾OpenGL应用编程接口，为后续章节中的材质铺垫基础。这并不是详尽的回顾。如果你已经
非常熟悉OpenGL，那么可以放心跳过本章提前进入下一章的学习。如果你熟悉另一种3D图形API，那么
你可以在这里汲取足够的OpenGL相关的信息来开始使用OpenGL着色器语言用于着色器开发。除非另行说明，
OpenGL功能描述基于OpenGL 2.0版本。
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This chapter briefly reviews the OpenGL application programming interface to lay the foundation
for the material in subsequent chapters. It is not an exhaustive overview. If you are already
extremely familiar with OpenGL, you can safely skip ahead to the next chapter. If you are
familiar with another 3D graphics API, you can glean enough information here about OpenGL to
begin using the OpenGL Shading Language for shader development.
Unless otherwise noted, descriptions of OpenGL functionality are based on the OpenGL 2.0
specification.