HP-GL, short for Hewlett-Packard Graphics Language and often written as HPGL, is a page description language created by Hewlett-Packard (HP). HP-GL was the primary page description language used by HP plotters. It was introduced with the plotter HP-9872 in 1977 and became a standard for almost all plotters. Hewlett-Packard's printers also usually support HP-GL/2 in addition to PCL.
Design The language is formed from a series of two letter codes (mnemonics), followed by optional parameters. For instance an arc can be drawn on a page by sending the string: AA100,100,50; This means Arc Absolute, and the parameters place the center of the arc at absolute coordinates 100,100 on the page, with a starting angle of 50 degrees measured counter-clockwise. A fourth optional parameter (not used here) specifies how far the arc continues, and defaults to 5 degrees. When first introduced, HP-GL contained the following commands:
Formats:
[i]: integer formats between -32767 and 32768. No decimal point. [d]: decimal format between +/- 127.9999. Optional decimal point. [c]: ASCII character
Examples Typical HP-GL files start with a few setup commands, followed by a long string of graphics commands. The file was in ASCII (text file) format, for instance:
The coordinate system was based on the smallest units one of the HP plotters could support, and was set to 25 μm (i.e. 40 units per millimeter, 1016 per inch). The coordinate space was positive or negative floating point numbers, specifically ±230.
HP-GL/2 The original HP-GL language did not support definition of line width, as this parameter was determined by the pens loaded into the plotter. With the advent of the first inkjet plotters, line width for the "pens" specified within the HP-GL files had to be set at the printer so it would know what line width to print for each pen, a cumbersome and error-prone process. With Hewlett-Packard Graphics Language/2 a.k.a. HP-GL/2, definition of line width was introduced into the language and allowed for elimination of this step. Also, among other improvements a binary file format was defined that allowed for smaller files and shorter file transfer times, and the minimal resolution was reduced.
AGL HP-GL is related to AGL (A Graphics Language), an extension of the BASIC programming language. AGL was implemented on Hewlett-Packard minicomputers to simplify controlling a plotter. AGL commands describe the desired graphics plotting function, which the computer relays as several HP-GL instructions to the plotter.
See also DMPL, another plotter language by Houston Instruments Gerber format is another plot-description format Logo, a computer language with drawing commands similar to HP-GL
References
Further reading Hewlett-Packard Company, Barcelona Division (September 1996) [1990]. The HP-GL/2 and HP RTL Reference Guide - A handbook for Program Developers - Hewlett-Packard Graphics Language/2 - Hewlett-Packard Raster Transfer Language (draft 2, second ed.). Barcelona, Spain: Addison-Wesley Publishing Company. ISBN 0-201-63325-6. HP Part No. 5961-3526, 5959-9733. Archived from the original on 2017-02-27. Retrieved 2017-02-28.
External links "Hewlett-Packard Graphics Language Commands". Archived from the original on 2017-02-27. "HP-GL Overview" (PDF). Archived from the original (PDF) on 2018-06-13. "Chiplotle". Retrieved 2023-02-15. – a Python-based HP-GL plotter control library for using vintage pen plotters with contemporary operating systems