ReGIS

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ReGIS, short for Remote Graphic Instruction Set, was a vector graphics markup language developed by Digital Equipment Corporation (DEC) for later models of their famous VT series of computer terminals. ReGIS supported rudimentary vector graphics consisting of lines, circular arcs, and similar shapes. Terminals supporting ReGIS generally allowed graphics and text to be mixed on-screen, which made construction of graphs and charts relatively easy.

Digital Equipment Corporation (DEC), using the trademark Digital, was a major American company in the computer industry from the 1950s to the 1990s.

VT100 computer terminal

The VT100 is a video terminal, introduced in August 1978 by Digital Equipment Corporation (DEC). It was one of the first terminals to support ANSI escape codes for cursor control and other tasks, and added a number of extended codes for special features like controlling the status lights on the keyboard. This led to rapid uptake of the ANSI standard, becoming the de facto standard for terminal emulators.

Computer terminal computer input/output device; an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system

A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying or printing data from, a computer or a computing system. The teletype was an example of an early day hardcopy terminal, and predated the use of a computer screen by decades.

Contents

History

ReGIS was first introduced on the VT125 in July 1981, followed shortly thereafter by the VK100 "GIGI" which combined the VT125 display system with composite video output and a BASIC interpreter. Later versions of the VT series included ReGIS, often with color support as well. This included the VT240 and 241 and the VT330 and 340. ReGIS is also supported by a small number of terminal emulator systems.

Composite video analog video transmission

Composite video is an analog video transmission that carries standard definition video typically at 480i or 576i resolution as a single channel. Video information is encoded on one channel, unlike the higher-quality S-video and the even higher-quality component video. In all of these video formats, audio is carried on a separate connection.

VT220

The VT220 is an ANSI standard computer terminal introduced by Digital Equipment Corporation (DEC) in 1983. The VT240 added monochrome ReGIS vector graphics support to the base model, while the VT241 did the same in color. The 200 series replaced the successful VT100 series, providing more functionality in a much smaller unit with a much smaller and lighter keyboard. Among its major upgrades was a number of international character sets, as well as the ability to define new character sets.

VT320

The VT320 was an ANSI standard computer terminal introduced by Digital Equipment Corporation (DEC) in 1987. The VT320 was the text-only version, while the VT330 added monochrome ReGIS, Sixel and Tektronix 4010 graphics, and the VT340 added color.

ReGIS replaced an earlier system known as waveform graphics that had been introduced on the VT55 and later used on the VT105. DEC normally provided backward compatibility with their terminals, but in this case the waveform system was simply dropped when ReGIS was introduced.

Waveform graphics

Waveform graphics is a simple vector graphics system introduced by Digital Equipment Corporation (DEC) on the VT55 and VT105 terminals in the mid-1970s. It was used to produce graphics output from mainframes and minicomputers. DEC used the term "waveform graphics" to refer specifically to the hardware, but it was used more generally to describe the whole system.

Description

ReGIS consisted of five primary drawing commands and a selection of status and device control commands. ReGIS mode was entered by specifying the escape code sequence ESCP0p, and exited with ESC\. The sequence ESCP is the generic Device Control String (DCS) used in the VT series of terminals, and is also used for a variety of other commands. The digit following the DCS was optional and specified a mode, in this case mode 0. Mode 0 was the default and picked up drawing where it left off, 1 reset the system to a blank slate, and 2 and 3 were the same as 0 and 1, but left a single line of text at the bottom of the screen for entering commands.

All drawing was based on an active pen location. Any command that moved the pen left it there for the next operation, similar to the operation of a mechanical plotter. The coordinate system was 0 to 799 in the X axis, and 0 to 479 in Y, with 0,0 in the upper left. In early implementations such as the VK100 and VT125, the actual device resolution was only 240 pixels, so the Y coordinates were "folded" so odd and even coordinates were the same location on the screen. Later models, starting with the VT240 and VT241, provided the full 480 pixel vertical resolution. The coordinate system could also be set by the user.

Plotter computer output device that draws on paper by moving a pen

The plotter is a computer printer for printing vector graphics. Plotters draw pictures on paper using a pen. In the past, plotters were used in applications such as computer-aided design, as they were able to produce line drawings much faster and of a higher quality than contemporary conventional printers, and small desktop plotters were often used for business graphics. Although they retained a niche for producing very large drawings for many years, plotters have now largely been replaced by wide-format conventional printers.

Coordinates could be pushed or pulled from a stack, and every command allowed the stack to be used as a parameter, the "b" parameter pushed the current coordinates on the stack, "e" popped it back off again. Coordinates could be specified in absolute or relative terms;

[200,100] is an absolute position at x=200, y=100 [+200,-100] is a relative position at x=current X+200, y=current Y-100 [200] is absolute x=200, y=unchanged (same as [200,+0]) [,-100] is relative, x=unchanged, y=current Y-100

There were four main drawing commands and three control commands;

P "Position", move the pen V "Vector", draw a line C "Curve", draw a circle (C) or arc (A) F "Fill", draws a filled polygon T "Text", output the following string of text S "Screen", a catch-all command for setting a wide variety of modes R "Report", outputs current status W "Write", sets the pen parameters L "Load", loads an alternate character set @ "Macrograph", see below

Each of these commands used the various coordinate modes in different ways, and some had additional parameters that were enclosed in parentheses. Commands could be followed by one or more parameters, allowing continued drawing from a single command. The interpreter was not case sensitive.

Some ReGIS terminals supported color, using a series of registers. These could be set with the S command using a variety of color input styles. s(m3(r100g0b0)) sets color register ("map") 3 to "r"ed using the RGB color system, while s(m3(h120l50s100)) does the same using the HSV system. The W command likewise set a wide variety of different styles, mostly for masking, fills and brushes.

HSL and HSV are alternative representations of the RGB color model, designed in the 1970s by computer graphics researchers to more closely align with the way human vision perceives color-making attributes. In these models, colors of each hue are arranged in a radial slice, around a central axis of neutral colors which ranges from black at the bottom to white at the top. The HSV representation models the way paints of different colors mix together, with the saturation dimension resembling various shades of brightly colored paint, and the value dimension resembling the mixture of those paints with varying amounts of black or white paint. The HSL model attempts to resemble more perceptual color models such as the Natural Color System (NCS) or Munsell color system, placing fully saturated colors around a circle at a lightness value of ​12, where a lightness value of 0 or 1 is fully black or white, respectively.

Finally, ReGIS allowed commands to be stored into a macrograph and then recalled using the @ operator. Up to 10,000 characters of code could be stored in the macros, each named with a single letter. The advantage was that the series of operations in the macro could be invoked by sending only two characters over the serial port, as opposed to the entire sequence of commands.

Sample

Example ReGIS code displayed on an xterm emulating a VT340 terminal. ReGIS circle.png
Example ReGIS code displayed on an xterm emulating a VT340 terminal.
<ESC>P0p S(E)(C1) P[100,440] V(B),[+100,+0],[+0,-10],[-100,+0],(E) P[500,300],F(C[+100]) <ESC>\

This code enters ReGIS mode and uses the S command to erase the screen with (E) and then turns on the visible cursor with (C1). P[100,440] moves the pen to 100,440 absolute. V(B),[+100,+0],[+0,-10],[-100,+0],(E) draws a series of lines, first pushing the current pen location onto the stack with (B), then drawing three lines using relative coordinates, and then using (E) to pop the previously saved location off the stack and draw to it. The result is a rectangle 100 by 10 pixels in size.

P[500,300],F(C[+100]) then moves to a new location, and uses the "F"ill command to wrap a "C"ircle. The fill command could wrap any number of commands within its parentheses, allowing it to fill complex shapes. It also allowed the inclusion of a "temporary write" that allowed the programmer to set the fill style within the fill, and abandon it as soon as it ended.

See also

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VT420

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VT520

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References