Graphics

PowerVision

Introduction

General

The PowerVision graphics subsystem is the "second generation" of graphics options available for the Silicon Graphics PowerSeries (and Crimson) machines and is the first to feature hardware texture support. VGX was introduced around 1990, VGXT a bit later. VGXT has "better" texture support (higher fill rate, perspective textures) - the "T" or the lack thereof does not mean that VGXT supports textures in hardware and VGX not.

One of the most interesting systems of this era is the Silicon Graphics Skywriter which is a multiprocessor PowerSeries system in a Rackmount enclosure with two VGX(T) graphics subsystems capable of driving two completely independent displays. So Skywriter is not the name of a graphics option or a basic machine, it is a name of a specialized configuration.

Features

PowerVision Graphics (VGX and VGXT) includes: 
24-bit color, double buffered 
8-bit alpha (transparency), double buffered 
24-bit Z-buffer 
8 stencil bitplanes 
4 Overlay (8 planes, double buffered [optional]) and 8 Window planes 
1280 x 1024 standard screen resolution 
Programmable video timing up to HDTV (1920 x 1024 @ 30Hz Interlaced) 
Support for live video input and output options 
Optional genlock capability 
Stereoscopic viewing support/Stereo-ready monitor 

Advanced graphics features include hardware support for: 
Subpixel positioning 
Advanced lighting models: 
Multiple colored light sources (up to 8) 
Ambient, diffuse, and specular lighting models 
Phong lighting 
Real-Time Texture Mapping 
Real-Time Anti-aliasing of all Primitives (polycons, lines, points) 
Spotlights (Local and infinite light source positioning; Two-sided lighting) 
High-speed graphics DMA with pan and zoom capabilities 
Atmospheric effects 
Sphere rendering 
Pixel-blending capabilities for transparency effects 
Full scene anti-allasing 
Soft shadows and depth-of-field 
FFTs and convolutions 
Multimode windowing environment

VGX vs. VGXT

As previously stated the obvious difference is that VGX uses a RM2 and the VGXT a RM3 Raster Manager board. Although they both support textures (so that is not what the "T" stands for!) there are significant differences. The RM2 uses IMP3 image engines, while the RM3 uses IMP5. This leads to the following basic differences/improvements:

• higher pixel fill rate - for bilinear mipmapped textures 50M pixels/sec (VGXT) instead of 17M pixels/sec (VGX)
• per pixel fog and haze computations added on VGXT
• per pixel perspective correction for textures added on VGXT
• more efficient texture memory usage on VGXT - textures can span memory bank boundaries on VGXT, while VGX does not allow that

Technology

Boards

VGX

GE6

Geometry Engine Board

GM3

Graphics Manager Board

RM2

Raster Manager Board which uses 20 IMP3 IMage Processing engines. A VGX setup can contain one (5-span VGX) or two (10-span VGX) Raster Manager Boards.

DG1

Display Generator Board

The DG1 board has 5 connectors on the card edge. Their function is as follows (top to bottom):

1. GENLOCK sync output
2. Alpha output
3. RGB video out and sync to monitor (BNC)
4. Super VHS and composite video (used if you have EV1 video option)
5. GENLOCK RGB input

VGXT

GE6

Geometry Engine Board

GM3 or GM3B

Graphics Manager Board

RM2

Raster Manager Board which uses 20 IMP5 IMage Processing engines. A VGXT setup can contain one (5-span VGXT) or two (10-span VGXT) Raster Manager Boards.

DG1

Display Generator Board

The DG1 board has 5 connectors on the card edge. Their function is as follows (top to bottom):

1. GENLOCK sync output
2. Alpha output
3. RGB video out and sync to monitor (BNC)
4. Super VHS and composite video (used if you have EV1 video option)
5. GENLOCK RGB input

Skywriter

A Skywriter uses two complete VGXT boardsets accompanied by the VX1 board that allows it to generate 2 seperate displays or one display with both VGXT boardsets working on it ("cyclops mode").

Setup

VGX

The following shows the configuration for a 15 slot TwinTower (PowerSeries) system:

The following shows the configuration for a SingleTower (PowerSeries) system:

The following shows the configuration for a Rack (PowerSeries) system:

VGXT

The following shows the configuration for a 15 slot TwinTower (PowerSeries) system:

The following shows the configuration for a SingleTower (PowerSeries) system:

The following shows the configuration for a Rack (PowerSeries) system:

The following shows the configuration for a Skywriter (PowerSeries) system:

Pictures

VGX Graphics Manager (GM3).

VGX Geometry Engine (GE6).

VGX Raster Manager (RM2).

VGX Display Generator (DG1)

VGX card edge connector.

Links