Define: Back-Face Culling this instructs OpenGL not to render triangles that are orientated away from the Camera...

[References]

1. "introduction to shader programming with Cg3.1"

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Back-Face Culling

As an optimization for very complex models, you may want to enable back-face culling which instructs OpenGL not to render triangles that are orientated away from the camera.

The direction a triangle is facing is determined by the order in which the triangles’s vertices are drawn. 

• By default, triangles whose vertices are drawn in a counter-clockwise order are considered “front-facing” polygons and are passed on to the rasterization unit 
• and polygons who’s vertices are drawn in a clock-wise order are considered “back-facing” polygons. 
• If back-face culling is enabled (with glEnable( GL_CULL_FACE )) then these polygons will not be passed to the rasterization unit.

With this in mind, we must take special care that the indices in the index buffer are specified in the correct order. Usually you won’t need to do this yourself. Most digital content creation software packages will take care of this detail for you but you should be aware of it in case you get a model from a modeling package that assumes that clock-wise facing polyons are “front-facing”. What you’ll see is a model that is viewable from the inside when you enable back-face culling.

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