Polygon

A polygon (also "primitive" or "triangle") is the most basic element of a 3D mesh. Each polygon is defined by three indices, each of which specifies a single vertex.

Correlation with Indices and Vertices

Each polygon is a triangle comprised of three indices. Each index references a single vertex, meaning that each polygon is comprised of three vertices. In aggregate, however, a polygon mesh does not have a 1:3 mapping between polygons and vertices, because multiple polygons may share any given vertex. There are at most three vertices per polygon in a mesh, however a typical contiguous mesh will be closer to one vertex per polygon (with each vertex shared by three polygons). The sharing efficiency depends on the structure of the mesh and whether the mesh is "smoothed".

Impact on Performance

Polygon count is often used as a proxy for performance impact. While it is true that polygon count is an important measure, this is only one of many possible factors contributing to rendering performance. It is important to consider the polygon count in the actual scene (ie. rendered on screen at the same time) as opposed to the polygon count on disk. Techniques such as Level of Detail may substantially reduce the polygon count in the scene if applied correctly.

The number of draw calls and the amount of overdraw also contribute to rendering performance.

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