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Nonplanar Polygons

Since OpenGL vertices are always three-dimensional, the points forming the boundary of a particular polygon do not necessarily lie on the same plane in space.

If a polygon's vertices do not lie in the same plane, then after various rotations in space, changes in the viewpoint, and projection onto the display screen, the points might no longer form a simple convex polygon.

For example, a four-point quadrilateral where the points are slightly out of plane, and look at it almost edge-on. You can get a nonsimple polygon that resembles a bow tie:

[IMAGE]

Nonplanar Polygon Transformed to Nonsimple Polygon