82845G Datasheet, PDF (120/193 Pages) Intel Corporation – Intel 82845G/82845GL/82845GV Graphics and Memory Controller Hub (GMCH)

Functional Description
4.4.1
4.4.1.1
The entire IGD is fed with data from the memory controller. The performance of the IGD is
directly related to the amount of bandwidth available. If the engines are not receiving data fast
enough from the memory controller (e.g., PC133), the rest of the IGD will also be affected.
The rest of this section focuses on explaining the IGD components and dependencies.
3D Engine
The 3D engine of the GMCH has been designed with a deep pipelined architecture, where
performance is maximized by allowing each stage of the pipeline to simultaneously operate on
different primitives or portions of the same primitive. The GMCH supports Perspective-correct
Texture Mapping, Multitextures, Bump-Mapping, Cubic Environment Maps, Bilinear, Trilinear
and Anisotropic MIP mapped filtering, Gouraud shading, Alpha-blending, Vertex and Per Pixel
Fog and Z/W Buffering.
The 3D pipeline subsystem performs the 3D rendering acceleration. The main blocks of the
pipeline are the Setup Engine, Scan Converter, Texture Pipeline, and Raster Pipeline. A typical
programming sequence would be to send instructions to set the state of the pipeline followed by
rendering instructions containing 3D primitive vertex data.
Setup Engine
The setup stage of the pipeline takes the input data associated with each vertex of a 3D primitive
and computes the various parameters required for scan conversion. In formatting this data, the
GMCH maintains sub-pixel accuracy.
3D Primitives and Data Formats Support
The 3D primitives rendered by GMCH are points, lines, discrete triangles, line strips, triangle
strips, triangle fans, polygons, indexed vertices as well as state variables. In addition to this, the
GMCH supports DirectX’s Flexible Vertex Format (FVF) that enables the application to specify a
variable length of parameter list obviating the need for sending unused information to the
hardware. Strips, Fans, and Indexed Vertices, as well as FVF, improves delivered vertex rate to the
setup engine significantly.
Pixel Accurate “Fast” Scissoring and Clipping Operation
The GMCH supports 2D clipping to a scissor rectangle within the drawing window. Objects are
clipped to the scissor rectangle, avoiding processing pixels that fall outside the rectangle. The
GMCH’s clipping and scissoring in hardware reduce the need for software to clip objects; this
improves performance. During the setup stage, the GMCH clips objects to the scissor window.
A scissor rectangle accelerates the clipping process by allowing the driver to clip to a bigger region
than the hardware renders to. The scissor rectangle needs to be pixel accurate, and independent of
line and point width. The GMCH will support a single scissor box rectangle, which can be enabled
or disabled.
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Intel^® 82845G/82845GL/82845GV GMCH Datasheet