Vector General
In contrast to similar terminals from other vendors, the Vector General systems included little internal memory.
This meant that the terminals did not need much storage of their own, and gave them the ability to rapidly access the data without it being copied over a slower link like the serial-based Tektronix 4010 or similar systems.
[b] The basic concept was that the host computer would run calculations to produce a series of points for the 2D or 3D model and express that as 12-bit values, normally stored in 16-bit words with extra stuffed status bits.
The most basic system included the hardware needed to pan and zoom 2D images, in which case the terminal containing it would be known as a Vector General 2D.
[10] The square CRTs were driven directly from the output of the transformation hardware, as opposed to being displayed using a traditional raster scanning method.
This could halve the number of points needed to describe a complete drawing, if the data was continuous like a line chart.
[16] The system also had a separate circuit to generate circular arcs, as opposed to having to send in a series of points.
When this value was not used, the coordinate system represented a physical area about twice as large as the screen, allowing it to translate the image to provide scrolling.
[19] The optional character generator drew characters using a set of five hardware-defined shapes, a circle, a square with a vertical line in the middle, a square with a horizontal line in the middle, and hourglass shapes oriented vertically and a similar one oriented horizontally.
[20] The system included a number of greek letters and mathematical symbols in addition to the normal ASCII characters.
[21] The terminal periodically read the main memory of the host computer using DMA to refresh the display.
[25] The VG3D is historically notable for its use in Star Wars, but is also well known for its early role in the development of computer aided design.
To film the images frame-by-frame, a wire was connected between one of the lights on the pushbutton panel and the shutter trigger on the camera.
This was triggered by the host computer, causing the camera to release the shutter one time and to advance the film a single frame.
The model consisted of a simple series of 3D points representing the outline of the station held in the PDP-11's memory, constructed algorithmically using the associated GRASS programming language's curve generation code.
[28] Mike Muuss recounts that the US Army's Ballistic Research Laboratory had purchased a Cyber 173 and three workstations consisting of a VG3D terminal and a PDP-11/34 to drive it.
He was bothered to see all of this hardware being wasted, so in 1979 he hooked up one of the workstations and created a program that produced a rotating 3D cube.
[29] Another programmer had been given a set of 3D points of the XM1 tank design and was writing code to output it to a Calcomp plotter.
He first output it as a static image on a Tektronix 4014, but the next night managed to get the display onto the VG3D where it could be easily spun around using the internal vector hardware.
