**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.
\

- Thus, if , then cull polygon.
- Note that
*V*is vector from eye to point on polygonYou 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.
\

- 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).

CS488/688: Introduction to Interactive Computer Graphics

University of Waterloo

Computer Graphics Lab