HPGL

HPGL, sometimes hyphenated as HP-GL, is the primary printer control language used by Hewlett-Packard plotters. The name is an acronym for Hewlett-Packard Graphics Language. It later became a standard for almost all plotters.

The language is formed from a series of two letter codes, 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 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.

Typical HPGL files started with a few setup commands, followed by a long string of graphics commands. For instance:

An example HPGL file

Command	Meaning
IN;	initialize, start a plotting job
IP;	set the initial point (origin), in this case the default 0,0
SC0,100,0,100;	set the scale so the page is 0 to 100 in both X and Y directions
SP1;	select pen 1
PD100,0,100,100,0,100,0,0;	put down the pen and move to the following locations (draw a box around the page)
PU50,50;	lift the pen and move to 50,50
CI25;	draw a circle with radius 25
SS;	select the standard font
DT*,1;	set the text delimiter to the asterisk, and don't print them (the 1, meaning "true")
PU20,80;	lift the pen and move to 20,80
LBHello World*;	draw a label

The coordinate system was based on the smallest units one of their plotters could support, and was set to 0.025mm. The coordinate space was positive or negative floating point numbers, specifically + or - 2³⁰.

Links:

Hewlett Packard Graphics Language Commands (http://www.sxlist.com/techref/language/hpgl/commands.htm)