Back-Face Culling
Back-face culling addresses a special case of occlusion called convex self-occlusion.
Basically, if an object is closed (having a well defined inside and outside) then some parts
of the outer surface must be blocked by other parts of the same surface.
We'll be more precise with our definitions in a minute.
On such surfaces we need only consider the normals of surface elements to determine if
they are invisible.
We can apply back-face culling to any orientable two-manifold.
Orientable two-manifolds have the following properties.
- Everywhere on their surface, they are locally like a plane.
They have no holes, cracks, or self-intersections.
- Their boundary partitions 3D space into interior and exterior regions.
In our case, manifolds will be composite objects made of many primitives, generally triangles.
Back-face culling eliminates a subset of these primitives & assumes that you are outside of all objects.
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