What are some concepts every OpenGL programer whether new or old should know from memory without having to look at documentation?

Off the top of my head I can think of:
  • Creating a window
  • Receiving user input from the keyboard and mouse
  • How to implement textures
  • Creating basic geometric figures
  • Animation
  • Double Buffering
  • Creating a game loop
  • Preventing memory leaks
  • Camera control
  • Lighting
  • Shading

Please post what you think should be added to the list!