
Bt2166
Graphics/Video Controller
Brooktree
2
PRODUCT DESCRIPTION
Introduction
L2166_A
By connecting a Brooktree video decoder such as the Bt829A, the Bt2166 sys-
tem can be used for applications such as video telephony and cable TV. Using the
Brooktree Bt829A VideoStream Decoder, the system supports the Intel/Microsoft/
NBC Intercast system to encode data within the vertical blanking interval of broad-
cast TV and deliver high-bandwidth World Wide Web content to the desktop.
High-Performance 3D
Graphics Acceleration
The Bt2166 delivers arcade-quality 3D graphics game performance using the pow-
erful combination of a triangle-setup engine and a tightly-coupled, dedicated, 3D
rendering engine to accelerate rendering of perspective-correct, texture-mapped,
Z-buffered, alpha-blended, Gouraud-shaded triangles. The combination of 3D
hardware setup and rendering engines enables a well-balanced, high-performance
3D graphics system. In general, geometry processing will be performed by the
CPU and implementation of both triangle setup and rendering hardware in the
graphics controller will help prevent the 3D pipeline performance from being lim-
ited by the CPU.
The triangle-setup processor provides line slope and color/texture differential
calculations for line, triangle and at top/bottom quadrilateral primitives and re-
trieves and stores the triangle list vertex data including coordinates, color, texture,
depth, and opacity parameters after polygon geometry processing. The Bt2166 tri-
angle set-up engine is implemented as a programmable, 32-bit RISC pipelined
processor, enabling parallel-processing with full overlap of the geometry and ren-
dering tasks. It provides the exibility to either completely off-load or assist the
host CPU in 3D triangle processing. Additionally, the setup coprocessor can per-
form other tasks such as triangle back-face culling and it can be easily optimized
to efciently handle different data structures related to specic 3D software en-
gines and APIs.
The Bt2166 3D triangle setup engine balances the 3D pipeline performance by
freeing up additional host CPU resources to apply to geometry processing and
game play tasks e.g. articial intelligence, audio, communications and user inter-
face I/O. With game play absorbing up to 70% of CPU resources in a typical title,
limited processor power is left to perform geometry and triangle setup. A 3D pipe-
line partitioning using a exible triangle setup processor in hardware facilitates
host geometry processing — enabling a more realistic game playing experience
than is possible using accelerators providing rendering only hardware.
The 3D rendering engine is a heavily pipelined, pixel processor which supports
both unmeshed and meshed (tri-strip) triangles. The system includes a dedicated
triangle-edge interpolation engine and a tightly-linked triangle rasterization engine
performing span interpolation, texture mapping, Z-buffering, alpha blending, and
lighting tasks. The triangle-edge interpolation engine and setup engine perform the
scan conversion process needed to transform a triangle dened by three vertices
into a set of data that represents the triangle spans (horizontal strips) required for
rendering. The edge interpolation process calculates rendering parameter values
required by the span interpolation engine. This includes determination of each set
of end point values per span and the value increment step per span for color, tex-
ture, depth, and opacity. Interpolation is performed with high precision, sub-pixel
accuracy.