New option to shift Z coordinates

lib/Slic3r.pm

@@ -29,6 +29,7 @@ use Slic3r::Surface::Collection;
 our $nozzle_diameter    = 0.45;
 our $print_center       = [100,100];  # object will be centered around this point
 our $use_relative_e_distances = 0;
+our $z_offset = 0;
 
 # filament options
 our $filament_diameter  = 3;    # mm

lib/Slic3r/Print.pm

@@ -187,7 +187,7 @@ sub export_gcode {
     foreach my $layer (@{ $self->layers }) {
         
         # go to layer
-        printf $fh $extruder->move_z($layer->z * $Slic3r::resolution);
+        printf $fh $extruder->move_z($Slic3r::z_offset + $layer->z * $Slic3r::resolution);
         
         # extrude skirts
         printf $fh $extruder->extrude_loop($_, 'skirt') for @{ $layer->skirts };

slic3r.pl

@@ -24,6 +24,7 @@ GetOptions(
     'nozzle-diameter=f'         => \$Slic3r::nozzle_diameter,
     'print-center=s'            => \$Slic3r::print_center,
     'use-relative-e-distances'  => \$Slic3r::use_relative_e_distances,
+    'z-offset=f'                => \$Slic3r::z_offset,
     
     # filament options
     'filament-diameter=f'           => \$Slic3r::filament_diameter,
@@ -137,6 +138,8 @@ Usage: slic3r.pl [ OPTIONS ] file.stl
                         (default: 100,100)
     --use-relative-e-distances
                         Use relative distances for extrusion in GCODE output
+    --z-offset          Additional height in mm to add to vertical coordinates
+                        (+/-, default: $Slic3r::z_offset)
     
   Filament options:
     --filament-diameter Diameter of your raw filament (default: $Slic3r::filament_diameter)