Backface Culling

Backface Culling

• A simple way to perform hidden surface is to remove all ``backfacing'' polygons.
• The observation is that if polygon normal is facing away from the viewer then it is ``backfacing.''
• For solid objects, this means the polygon will not be seen by the viewer.

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• Thus, if , then cull polygon.
• Note that V is vector from eye to point on polygon

  You cannot use the view direction for this.

Backface Culling

Not a complete solution

• If objects not convex, need to do more work.
• If polygons two sided (i.e., they do not enclose a volume) then we can't use it.

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• A HUGE speed advantage if we can use it since the test is cheap and we expect at least half the polygons will be discarded.
• Usually performed in conjunction with a more complete hidden surface algorithm.
• Easy to integrate into hardware (and usually improves performance by a factor of 2).