hi!

First of all, big ups to the inkscape developers! it is such a cool tool that has given me hours of fun with my axidraw... thanks for this marvelous piece of software!

I recently acquired a good old HP DraftPRO EXL (7576A) pen plotter. The plotter is in very good conditions and perfectly plots the demo drawing. I managed to communicate with it using a USB serial cable, and got inkscape 1.0 to plot stuff with it... but with weird results....  The drawings get broken, there appear lines which where not there, the plot stops without being complete, and even by repeatedly applying the plot command it will always stop on the same exact place without going further, leaving the drawing incomplete. This happens both with complex or super-simple graphics.

On the other side, i checked the hpgl conversion to make sure it was doing fine, and discovered that when reimporting hpgl files the drawings appear to be messed up. You can check the differences between the original svg (right) and the reimported hpgl (left):

https://www.dropbox.com/s/0imefr1qa0jiit6/Captura%20de%20Pantalla%202020-07-10%20a%20les%2023.14.31.png?dl=0

I don't know if the two things are related (faulty hpgl conversion and weird plotting behaviors)...

Does anyone encountered this kind of problems? and if so, how could this be solved?

I'm so happy with my new old plotter and would love to make cool stuff with it!

What happens when you re-export the import?  Also, I'd get a hpgl viewer to help.  Something that lets you view the hpgl outside inkscape, both before and after export import export.  I've used this one on Windows https://hpglviewer.com.

As to why, don't know.  Maybe inkscape exports fine but something is wrong with import.  An external viewer might help find the problem. Also note the plot extension is probably doing something separate from the import export, but not sure.  That is I don't know if plot makes it's own hpgl or uses the output of Inkscape's existing export ability.

If you do get a well formed file, confirmed with the external viewer, then you could always just send the file directly to the com port via the command line.  On Windows something like COPY yourfile.hpgl /B COM1 /B  though I haven't done this in a coon's age, you might have to triple check.  Probably need a command before that to set  the baud rate.  A mode command like MODE COM1 BAUD=9600 PARITY=n DATA=8

Lastly, I notice your canvas/page size does not match the artwork size.  I am not sure what this means for hpgl or what it does with off canvas or off page objects.  Maybe go into document preferences and set the page size to equal the artwork size, (select all objects first.)

Thanks for the tips phiscribe!

i just tried the hpgl with an external viewer as you suggested, and the mess looks the same, so i guess there's some kind of bug with the inkscape's svg to hpgl conversion

I'm going to try the command line control of the plotter as you suggested, to see if simple drawings get plotted correctly and figure out whether the problem with plotting comes from the plotter or from inkscape. I als ordered a new serial wire (i'm using a long db25 to db9 that came with the printer, 30 year old...) to make sure the problem is not there...

i'll keep you updated!