Print3r: Cura

Print3r can use Cura - more precisely the CuraEngine, which is embedded in Cura, which isn't readily to use in command-line mode but it's doable with these few hints.

Reference CuraEngine as slicer with --slicer=cura when calling print3r.

Infill vs Infill Line Distance

By default the infill density aka infill_spars_density [%] isn't available directly instead the infill_line_distance is the low-level setting with this relation as stated in fdmprinter.def.json, rewritten in pseudo code for readability:

infill_line_distance = infill_sparse_density == 0 ? 0 :
   (infill_line_width * 100) / infill_sparse_density * 
      (infill_pattern == 'grid' ? 2 : 
         (infill_pattern == 'triangles' || 
         infill_pattern == 'trihexagon' || 
         infill_pattern == 'cubic' || 
         infill_pattern == 'cubicsubdiv') ? 3 :
            (infill_pattern == 'tetrahedral' || infill_pattern == 'quarter_cubic' ? 2 : 
               infill_pattern == 'cross' || infill_pattern == 'cross_3d' ? 1 : 1
            )
         )
      )
   )

For 0.4mm nozzle printing a 0.4mm line width in general:

infill_line_distance = (0.4 * 100) / infill_sparse_density;

so for 20% infill you get infill_line_distance = 2mm.