The HP-GL Device

HP-GL (Hewlett-Packard Graphics Language) is a plotter control language used to produce graphics on a wide family of pen plotters. To use HP-GL as the current graphics device, issue the IDL command:

This causes IDL to use HP-GL for producing graphical output. Once the HP-GL driver is enabled via SET_PLOT, the DEVICE procedure is used to control its actions, as described below. The default settings for the HP-GL driver are shown in the following table. Use the statement:


Feature	Value
File	idl.hp
Orientation	Portrait
Erase	No action
Polygon filling	Software
Turn plotter logically on/off	No
Specify xon/xoff flow control	Yes
Horizontal offset	3/4 in.
Vertical offset	5 in.
Width	7 in.
Height	5 in.

Abilities And Limitations

IDL is able to produce a wide variety of graphical output using HP-GL. The following is a list of what is and is not supported:

All types of vector graphics can be generated, including line plots, contours, surfaces, etc.

HP-GL plotters can draw lines in different colors selected from the pen carousel. It should be noted that color tables are not used with HP-GL. Instead, each color index refers directly to one of the pens in the carousel.

Some HP-GL plotters can do polygon filling in hardware. Others can rely on the software polygon filling provided by IDL.

It is possible to generate graphics using the hardware generated text characters, although such characters do not give much improvement over the standard vector fonts. To use hardware characters, set the !P.FONT system variable to zero, or set the FONT keyword to the plotting routines to zero.

Since HP-GL is designed to drive pen plotters, it does not support the output of raster images. Therefore, TV and TVSCL do not work with HP-GL.

Since pen plotters are not interactive devices, they cannot support such operations as cursors and windows.

HP-GL Linestyles

The LINESTYLE graphics keyword allows specifying any of 6 linestyles. HP-GL does not support all of these linestyles, and styles 3 and 4 differ from the definition in Graphics Keywords. The following table summarizes the differences:


Index	Normal Line Style	HP-GL Line Style
0	Solid	same
1	Dotted	same
2	Dashed	same
3	Dash Dot	Relative size of dash and dot are different.
4	Dash Dot Dot Dot	Dash Dot Dot
5	Long Dashes	same

The HP-GL Device

Device Keywords Accepted by the HP-GL Device:

Abilities And Limitations

HP-GL Linestyles