The Tessellation Pipeline - Practical Rendering and Computation with Direct3D 11 - page 265

In the context of computer games, it was ID Software's id Tech 3 graphics engine,
used in Quake 3 Arena in December 1999, that made waves with regard to using curved
surfaces for real-time graphics.
In late 2001, ATI Technologies introduced the Radeon 8500 GPU, which included its
TruForm functionality (ATI, 2001). This was a first for commodity hardware, which, when
combined with Direct3D 8.1, allowed for hardware-accelerated tessellation of higher-order
surfaces.
The popularity and use of this pioneering new feature were short-lived, with the ad-
vent of the id Tech 4 engine (culminating in August, 2004's Doom 3) and real-time stencil
shadow techniques. Shadow volumes were a geometric technique that required processing
on the CPU for accurate results; this conflicted with TruForm, in which the finally rendered
geometry was different from that available to the CPU. Visible differences between the
silhouette of a model and its shadow made them incompatible. Ultimately, shadowing won
the popularity contest.
Interestingly, around the same time, Valve Software were working on its Source
Engine (culminating in Counterstrike: Source and Half Life 2, both released in summer,
2004). The Source Engine supported shadow mapping (Valve Software) as an equivalent
feature to id Tech 4's stencil shadows; in particular, this technique was compatible with
tessellated geometry.
Competition between hardware vendors and the two rival software engines was in-
tense. Ultimately, TruForm lost out, due to the popularity of stencil shadows and a lack of
universal support across all hardware vendors.
Following on from ID Software's id Tech 4, it became practical and desirable to sim-
ulate higher-resolution models by using low-density meshes and texture trickery. Tangent-
space normal mapping and related environment mapping techniques can represent the
lighting interactions of a geometrically complex surface, while still being texture-mapped
to a far simpler planar model. Although this is generally considered to be a reasonable
tradeoff between performance and image quality, it had a significant drawback, in that a
model's silhouette was still low-detail, which showed up the trick for what it truly was.
4.2 Tessellation and the Direct3D Pipeline
At first glance, the new tessellation stages that have been added in Direct3D 11 don't ap-
pear overly complex. But on closer inspection, we can see that when one is designing and
writing code, the flow of data and the responsibilities of each unit can quickly become
confusing. This is compounded because the deeper pipeline is harder to visualize—a clas-
sic pipeline consisting of a vertex shader and pixel shader was relatively simple, and small