3 ms·

Do you send the data and the labels to the plotter, or to the driver software running on your computer? I always imagined HP-GL would be a list of lines/curves,

Do you send the data and the labels to the plotter, or to the driver software running on your computer? I always imagined HP-GL would be a list of lines/curves, and that the plotter would plot them in whatever order they came in.

zabzonk 6y ago
I was using a CP/M computer - there was no driver architecture. You sent HP-GL instructions and data as text via the RS232 interface. The plotter obviously had a limited buffer size, which would prevent certain optimisations, but then so did the CP/M computer!
- rahimnathwani 6y ago
  So interesting! In the most recent reference guide I found just now, it seems you can draw a segment of a pie chart using a single EW (Edge Wedge) instruction but, for a complete pie chart, this method would require you to calculate the angles of each segment yourself. And of course to add the labels yourself. Perhaps I'm looking in the wrong place or perhaps the instruction to draw a whole pie chart has been deprecated.
  - zabzonk 6y ago
    You may be right - this was a looong time ago. Calculating the angles from the data is not difficult though, so I may have forgot that I did it. I can't really imagine calculating and placing the labels myself though, but perhaps I was cleverer then! Anyway, the HP pen plotter we had in the early 1980s was a very impressive device, when what we had were Z80 based computers driving them.
    - joshu 6y ago
      You misremember. It doesn't do any of that.
- yjftsjthsd-h 6y ago
  > The plotter obviously had a limited buffer size, which would prevent certain optimisations, but then so did the CP/M computer! Yeah, but which had more? :) Reminds me of that time in the 90s(?) when people connected printers to computers, but the printers had more powerful processors than the computers. (Or later, when someone poked into the WiFi board on their arduino and realized that it was a more powerful microcontroller, but that's not so directly related)
scruss 6y ago
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.

zabzonk 6y ago

I was using a CP/M computer - there was no driver architecture. You sent HP-GL instructions and data as text via the RS232 interface. The plotter obviously had a limited buffer size, which would prevent certain optimisations, but then so did the CP/M computer!

rahimnathwani 6y ago
So interesting! In the most recent reference guide I found just now, it seems you can draw a segment of a pie chart using a single EW (Edge Wedge) instruction but, for a complete pie chart, this method would require you to calculate the angles of each segment yourself. And of course to add the labels yourself. Perhaps I'm looking in the wrong place or perhaps the instruction to draw a whole pie chart has been deprecated.
- zabzonk 6y ago
  You may be right - this was a looong time ago. Calculating the angles from the data is not difficult though, so I may have forgot that I did it. I can't really imagine calculating and placing the labels myself though, but perhaps I was cleverer then! Anyway, the HP pen plotter we had in the early 1980s was a very impressive device, when what we had were Z80 based computers driving them.
  - joshu 6y ago
    You misremember. It doesn't do any of that.
yjftsjthsd-h 6y ago
> The plotter obviously had a limited buffer size, which would prevent certain optimisations, but then so did the CP/M computer! Yeah, but which had more? :) Reminds me of that time in the 90s(?) when people connected printers to computers, but the printers had more powerful processors than the computers. (Or later, when someone poked into the WiFi board on their arduino and realized that it was a more powerful microcontroller, but that's not so directly related)

scruss 6y ago

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.