Graphics Reference
In-Depth Information
Figure 4.11. DetailTessellation11 from the Microsoft DirectX SDK.
depicts the various tessellation levels (contrast the foreground and background) defined by
the underlying geometry.
Chapter 9 covers examples of tessellation algorithms, and the Microsoft DirectX
SDK includes several others.
4.3 Parameters forTessellation
In the preceding section, the detailed flow of execution and data revealed two stages where
amplification could occur. First, the hull shader could alter the number of control points
passed down the pipeline (3 vertices of a triangle become 10 control points on a cubic
surface). Secondly, the fixed-function tessellator generated a number of new primitives, ac-
cording to the output from the hull shader constant function (7 vertices defining 6 triangles).
As the author of Direct3D 11 shaders, you have full control over these amplifica-
tion steps.
Generally speaking, there are two scales to consider when deciding the level of am-
plification—quality and performance. In most cases, these will be inversely proportional,
such that higher quality implies greater amplification, which requires more processing and
hence reduces performance.
43.1 A Simple Example
Figure 4.12 demonstrates the performance-versus-quality decision. The green curve be-
hind the black arrows can be considered as the ideal surface—the one that an artist or
Search WWH ::




Custom Search