VAXstation 4000 Model 60's 3D Graphics Options

This document provides a technical summary of the VAXstation 4000 Model 60's 3D Graphics Options: SPXg and SPXgt. These are high-resolution (1280x1024) 3D graphics accelerators for the VAX/VMS environment.

Key features and distinctions:

• SPXg (8-plane, PV61G-BA): Suited for design automation, molecular modeling, and pseudo-color imaging. Supports full double buffering and 16-bit Z buffering.
• SPXgt (24-plane, PV61G-AA): Higher performance, suited for 3D modeling, true-color imaging, and visualization. Supports full double buffering and 24-bit Z buffering.

Both options offer hardware acceleration for 2D and 3D graphics primitives (vectors, polygons), animation, depth cueing, smooth shading, and Z buffering.

Software Architecture:

• They integrate with DECwindows (Digital's X Window System) and OSF/Motif graphical user interfaces.
• They utilize X Protocol Extensions like PEX (for 3D graphics), Display PostScript, and Xv (multimedia).
• They support high-level Graphics Programming Interfaces (APIs) including DEC PHIGS (with PHIGS PLUS), PEXlib, and GKS/GKS-3D.
• The XMAP video architecture manages multi-window displays, offering virtual mapping of resources and individual window control for multiple applications and visual types.

Hardware Architecture:

• A common architecture is employed, featuring a 3D rendering pipeline accelerated by specialized components.
• The Geometry Engine (an Intel i860 floating-point processor) performs 3D geometry and lighting calculations, transforming 3D scene data into 2D device coordinates.
• One or more Scan Conversion Processors (ScanProc+) then handle scan conversion, computing pixel addresses and values, and interpolating residual 3D data for features like smooth shading and Z-buffer hidden-surface removal.
• Other key components include the JChip for interface and control, SRAM for command FIFOs, VRAM/DRAM for frame buffers, and RAMDACs (Bt460 for SPXg, Bt463 for SPXgt) for digital-to-analog conversion and color lookup. The SPXgt also includes dedicated Bt431 cursor generators.

Performance:

• Both SPXg and SPXgt offer competitive 3D performance and significantly improved 2D fill and vector rates compared to previous SPX options, as measured by 3D Graphics Benchmarks and Picture-Level Benchmarks (PLB).