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DirectX 11 Tessellation Performance

Shapes that repeat over and over again over without gaps or overlapping create the visual effect called tessellation. In computer graphics, tessellation splits the geometric figures that compose three-dimensional models into smaller, finer parts. This effect creates smoother, more realistic surfaces with richer visual detail. Microsoft's DirectX 11, an application program interface for displaying multimedia such as 3-D games, supports advanced tessellation performance, meaning it allows game developers to take advantage of graphical techniques made possible solely by tessellation.

Displacement Mapping
- Displacement mapping gives normally flat textures a three-dimensional appearance by storing height information in the texture. This technique adds realism to surfaces such as roofing shingles or carvings. Because displacement mapping requires a large number of vertices, the technique relies on tessellation to create these advanced shapes. As a standard feature of DirectX 11, developers can take advantage of displacement mapping to improve the appearance of in-game graphics without taking a major performance hit.
Refinement Algorithms
- DirectX 11's tessellation features help developers take advantage of refinement algorithms, which use fine, tessellated polygons -- the triangles that compose three-dimensional models -- to smooth out models that may otherwise appear jagged, allowing for curved rather than blocky surfaces. DirectX 11 accommodates an algorithm known as PN-Triangles or N-patches to create these smooth, curved surfaces. With this technique, games no longer have to rely on simplistic, blocky shapes for efficient performance.
Level of Detail
- Without tessellation, three-dimensional games rely on tricks such as pop-in or texture draw-in -- detail or objects appearing only when the player is in close range -- to optimize performance. Games that use these techniques store models with varying levels of detail and swap them in on the fly. Via a DirectX 11-supported process known as dynamic tessellation, developers can improve performance by using only one model per object. The game initially renders the object in low detail when seen from a distance. Then, using the additional triangles provided by tessellation, the object gains detail as the player approaches.
Negative Effects on Performance
- Though proper use of tessellation takes advantage of techniques such as displacement mapping, refinement algorithms and dynamic level of detail, or LOD, to improve both performance and graphics, improper use of tessellation actually hampers game performance. For instance, when most polygons on a model cover one pixel or less, 3-D graphics performance suffers. As tessellation creates more polygons, it reduces the efficiency of the multisample antialiasing that helps smooth the appearance of individual pixels on polygon edges.

Computer Games