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# What Is Back-Face Culling?

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• Written By: Alex Newth
• Edited By: Angela B.
2003-2019
Conjecture Corporation
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Back-face culling is a rendering technique used in three-dimensional (3D) modeling for movies and games to help cut down on needed memory. When polygons are used, they point clockwise or counterclockwise and the user has to select what direction he or she wants to limit. After selecting this, back-face culling will take effect and make the other side of each polygon disappear, because they are not required. Based on how the player moves in a 3D game or through a 3D program, the polygons may toggle between invisible and visible. Fewer polygons will be needed overall, so the amount of memory and the processing requirements for the movie or game will be much less.

Polygons in a 3D game or movie often have a certain direction and winding and, for back-face culling to work, the user must select a direction to limit. For example, if clockwise polygons are limited, then any polygons that are moving clockwise will become invisible. The direction normally is selected based on the playerâ€™s common position, where the camera is located and how the general scenery is built.

Based on what the user chooses and how the camera or player moves, some or many of the polygons will disappear from the program. If the polygons still are needed to render an object, then the backside will become invisible, but they will not completely disappear from the program. For example, if the camera is looking head-on at an object, then the front and sides will be needed to compose the image but, since the backside is not seen, that angle will disappear.

In early 3D movies and games, it would be rare for the camera or player to see the backside of polygonal objects, so there was no need to rotate the viewable angle. More advanced 3D graphics often have an adjusting camera, so back-face culling does not just make polygons invisible. The invisible polygons will rotate based on where the user is moving. For example, if someone moves from the front to the back of a 3D object, then the polygons in the back will load as the user comes closer to the backside.

The purpose of back-face culling is to cut down on the amount of polygons required to run a 3D movie or game. Memory often runs high for many 3D projects, and this makes it harder to display and process the media. By reducing the number of required polygons, it becomes much easier for movies and games to be used in projectors or consumer-grade computers.