Frustum

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Frustum

A persistent problem for 3D rendering is the lack of memory and processing power, two things you can never have enough of. When computers were relatively slow, researchers needed a method that eliminated unwanted objects that weren't being utilized during rendering. This was a major problem because if the image plane didn't include a set of objects in its viewport, the computer algorithm would still process them. This extra unnecessary processing of objects outside the viewport made rendering images extremely slow. Eventually, researchers determined that you could create something called a frustum (a pyramid shaped looking object) to limit the viewing area of the scene. The frustum couldn't be a cube because objects appear larger the closer they are and smaller the farther away they are, so it had to be more advanced to handle the field of view. The frustum is constructed to block out certain objects in the scene that weren't in the viewable area of the observer. A frustum can be seen as a volume that encompasses a selected set of objects in the scene. This idea works well because the frustum basically only acknowledges objects that are within its volume and ignores the objects that are outside. This eliminates unwanted objects being sent through the rendering pipeline, thus saving lots of rendering time. This simple idea became common in 3D rendering applications, especially video games . See Figure 5.4 for an example of a frustum.

Figure 5.4. The frustum is a volume that encompasses a selected set of objects in the scene.

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