845GL datasheet(120/193 Pages) INTEL

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Functional Description

120

Intel® 82845G/82845GL/82845GV GMCH Datasheet

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.

4.4.1

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.

4.4.1.1

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.

845GL Datasheet(PDF) 120 Page - Intel Corporation