This repo documents the design of a graphics co-processor, along with some tools (assembler, debugger, simulator) and microcode. It was designed by Lawrence Kesteloot and Rob Wheeler in March 1995 for the University of North Carolina CS 265 (Computer Architecture) final project.
See the final write-up for the details.
The simulator was used to generate this teapot:
From the introduction of the write-up:
This document outlines the design of the Graphics Engine (GE), which has an optimized instruction set for transforming and rasterizing 3-D graphics primitives for low-end machines. The GE typically is included in home or arcade video game machines. A general-purpose CPU and the GE share memory for communication: The CPU calculates the game dynamics and sets up a graphics data structure (a display list of 3-D primitives) that the GE traverses and rasterizes in a pipeline arrangement. The GE has a RISC core with a back-end specialized for rasterizing triangles.
A typical application is a game that uses 3-D graphics along with sound and 2-D sprites (the latter two being supplied by other hardware). The application uses the GE to transform, light, and shade the generated geometry. A typical game might require up to 3,000 triangles per scene to achieve rendering detail comparable to current 2-D games. Thus, at 30 frames a second, roughly 100,000 triangles per second must be transformed and half of these must be lit and rasterized. (Over half of the triangles will be removed by backface and frustum culling.)
The GE instruction set is optimized for the following tasks:
- traversing a hierarchical display list;
- transforming coordinates;
- calculating plane equations; and
- rasterizing polygons.
Only minimal 3-D features are supported—clipping, diffuse lighting, Gouraud shading, screen-door transparency, and Z-buffering. The GE has no anti-aliasing, texturing, or blending support.
This is a very specialized CPU, not only because it is optimized for graphics, but because it is designed for low-end, inexpensive graphics. It does not provide the flexibility of high-end graphics workstations, and the game programmer is expected to abide by restrictions, such as keeping coordinates within the range of fixed-point values. When necessary, we simplified the hardware at the expense of a heavier burden on the programmer. Most game programmers are used to programming in assembler and having no programming support whatsoever, so these are not unusual nor unexpected demands.
Copyright 1995 Lawrence Kesteloot and Rob Wheeler
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