I have designed a few knitting patterns in gimp. One pixel per stitch works pretty well - until it's time to print the thing. This script expands your pattern (scale factor is user selectable) and draws it with black lines, thicker black lines every ten stitches. See Knitting wiki for an example.
Nov 2021: I have now made a similar script for kogin sashiko embroidery patterns. I'm adding modoko from koginbank.com to the Kogin_brushes directory, with all the small ones so far. Copy the ones you want to your brushes directory. See Kogin wiki for an example.
Place the *.py scripts in your plug-ins directory and the brushes in the brushes directory. The plug-ins should show up under the Image menu.
For GIMP 2.10, the files should go under:
$HOME/.gimp-2.10/plug-ins directory $HOME/.gimp-2.10/brushes directory
Make sure the scripts are executable:
chmod 755 *.py
On a Mac, the directories are now:
$HOME/Library/Application\ Support/GIMP/2.10/plug-ins $HOME/Library/Application\ Support/GIMP/2.10/brushes
I don't have a PC to test, so I don't know where to put things there.
Note: If you have an alpha channel, the results of the knitting script looks weird. Better to remove the alpha channel (image -> flatten), though that is a bug I might fix someday, someday.
I wish I knew how to make the brushes work with the foreground color. Is that on my end or GIMP's?