3D Graphics - Game Programming Algorithms and Techniques - page 77

Polygons
3D objects can be represented in a computer program in several ways, but the
vast majority of games choose to represent their 3D objects with poly-
gons—specifically, triangles.
Why triangles? First of all, they are the simplest polygon possible because they
can be represented by only three vertices , or the points on the corners of the poly-
gon. Second, triangles are guaranteed to lie on a single plane, whereas a polygon
with four or more vertices may lie on multiple planes. Finally, arbitrary 3D objects
easily tessellate into triangles without leaving holes or other deformations.
A single model, or mesh , is made up of a large number of triangles. The number
of triangles a particular mesh has depends on the platform constraints as well as
the particular use of the model. For an Xbox 360 game, a character model may
have 15,000polygons, whereas abarrel might berepresented byacouple hundred.
Figure 4.1 shows a mesh represented with triangles.
Figure 4.1 A sample mesh made with triangles.