Using HPGL as a drawing interchange media

Introduction

HPGL is the HP graphics language designed for specifying 2D graphical information for the HP range of plotters. It was not intended as an interchange format but some software suppliers use it as such. At least it is efficient and easy to write and read. This short note describes those aspects of the format which may be used to describe geometry. The language itself has a large number of instructions, most of the ones not touched on here relate directly to plotter devices, for a full description of the language the HPGL description is normally provided with an HPGL compatible plotter.

Basics

HPGL commands are basically two upper-case character instructions followed by any arguments, and finally ending in the separator character which is a semicolon by default. The arguments are normally separated by commas. String arguments are normally terminated by carriage return.

In what follows, all the standard HPGL commands are listed, those which are likely to be useful for data interchange will be discussed at the end of this document. Optional arguments for any command are shown in brackets.

Commands

     Instruction                Arguments
AA   Arc Absolute               x,y,angle(,tolerance)
AF   Advance page
AH   Advance page
AP   Automatic Pen Operations   n
AR   Arc Relative               x,y,angle(,tolerance)
AS   Acceleration Select        acceleration(,pennumber)
BF   Buffer Plot
BL   Buffer label               string
CA   Select Alternative Charset set
CC   Character chord angle      angle
CI   Circle                     radius(,tolerance)
CM   Character Selection Mode   switchmode(,fallbackmode)
CP   Character Plot             spaces,lines
CS   Select Standard Charset    set
CT   Chord Tolerance            n
CV   Curved line generator      n(,inputdelay)
CD   Digitize Clear
DF   Default
DI   Absolute Direction         run,rise
DL   Define Download character  charnumber(,pencontrol),x,y(...)
DP   Digitze Point
DR   Relative Direction         run.rise
DS   Designate Charset          slot,set
DT   Define Label Terminator    terminator
EA   Edge Rectangle Absolute    x,y
EP   Edge Polygon            
ER   Edge Rectangle Relative    x,y
ES   Extra Space                spaces(,lines)
EW   Edge Wedge                 radius,startangle,sweepangle(,tolerance)
FP   Fill Polygon            
FS   Force Select               force(.pennumber)
FT   Fill Type                  type(,spacing(,angle))
GC   Group Count                countnumber
GM   Graphics Memory            (polygonbuff)(,downloadbuff)(,replotbuff)(,vectorbuff)
GP   Group Pen                  (groupnumber(,pennumber(,numberofpens,(length))))
IM   Input Mask                 emaskvalue(,smaskvalue(,pmaskvalue))
IN   Initialize
IP   Input p1 and p2            x,y(,x,y)
IV   Invoke Character Slot      slot,(left)
IW   Input Window               x,y,x,y
KY   Define Key                 key(,function)
LB   Label                      string
LO   Label Origin               positionnumber
LT   Line Type                  patternnumber(,patternlength)
NR   Not Ready
PA   Plot Absolute              x,y(,...)
PB   Print Buffered Label
PD   Pen Down                   x,y(,...)
PG   Page Feed                  n
PM   Polygon Mode               n
PR   Plot Relative              x,y(,...)
PT   Pen Thickness              thickness
PU   Pen Up                     x,y(,...)
RA   Fill Rectangle Absolute    x,y
RO   Rotate Coordinate System   n
RP   Replot                     n
RR   Fill Rectangle Relative    x,y
SA   Select Alternative Charset      
SC   Scale                      x,y,x,y(,type(,left,bottom))
SG   Select Pen Group           groupnumber
SI   Absolute Character Size    width,height
SL   Character Slant            tantheta
SM   Symbol Mode                character
SP   Select Pen                 pennumber
SR   Relative Character Size    width,height
SS   Select Standard Charset 
TL   Tick Length                tp(,tn)
UC   User Defined Character     (pencontrol,)x,y
UF   User Defined Fill          gap1(,gap2,...gap20)
VS   Velocity Select            speed(,pennumber)
WD   Write to Display           string
WG   Fill Wedge                 radius,startangle,sweepangle(,tolerance)
XT   X Tick
YT   Y Tick

Output Instructions

The following instructions don't have any arguments but rather generate output from the plotting device. They are of no use for interchanging geometric data and therefore the form of the output is not discussed. See an HPGL reference book.

OA   Output Actual Position
OC   Output Position
OD   Output Digitised Point
OE   Output Error
OF   Output Factors
OG   Output Group Count
OH   Output HardClip Limits
OI   Output Identification
OK   Output Key
OL   Output Label Length
OO   Output Options
OP   Output p1 and p2
OS   Output Status
OT   Output Carousel Type
OW   Output Window

Escape sequences

The following escape sequences are generally only applicable when connected through a serial interface to a physical plotter, they have nothing to do with data interchange and so their arguments will not be listed nor will the form of the output most of them create .

esc@ Set Plotter Configuration
escA Output Identification
escB Output Buffer Space
escE Output Extended error
escH Set Handshake Mode 1
escI Set Handshake Mode 2
escJ Abort Device Control
escK Abort Graphics
escL Output Buffer Size When Empty
escM Set Output Mode
escN Set Extended Output and Handshake Mode
escO Output Extended Status
escP Set Handshake Mode
escQ Set Monitor Mode
escR Reset
escS Output Configurable Memory
escT Allocate Configurable Memory
escU End Flush Mode
escY Plotter On
esc( Plotter On
escZ Plotter Off
esc) Plotter Off

Useful Commands with examples

Since plotters are very basic line drawing hardware devices it is not surprising that the most commonly used commands are those that draw lines from one point to another.

Pen up and down dictate when a line is actually being created, the plot commands do the movement between points.

For example to draw a line from (1,0) to (2,0) might be specified as follows

There are two basic attributes that can be assigned to a line, as expected they are actually applied to the pens of the plotting device. They are:

The pen number normally acts as an indexed colour system, most commonly there are only 8 pens (colour) available.

There are a large number of settings for controlling text, these and further details of the above instructions will be left to the reader to experiment with or read in the full HPGL manuals.