[scruss]

HP-GL was always able to plot text labels and make graph data markers: it was meant for scientific graphs, after all. Later plotters added arc sectors and filled (hatched) polygons. All the clever optimization was handled by the host computer: a plotter will just output what you tell it.

There is a feature in HP-GL that does make certain types of XY plotting simpler. While it's not a programming language like PostScript, you can scale, rotate and offset the plot by arbitrary amounts. HP instrumentation manuals claimed it was possible to directly plot experimental data by feeding it straight to the plotter after setting the scale. I feel this was a highly aspirational statement, and one not seeing much real use.