G-code postprocessing script to modify first layer travel speed

limit_first_layer_travel_speed.py

#!/usr/bin/env python3
# Copyright (c) Sean C. Monahan
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"""in Post-processing scripts, put:
{full-path-to-this-file} {your-desired-first-layer-travel-speed-in-mm-per-second}

(On Windows, I think it would be
{path-to-your-python-interpreter} {full-path-to-this-file} {your-desired-first-layer-travel-speed-in-mm-per-second}
)

This will modify the gcode output to change first layer travel moves to use the specified speed.
This is hacky as heck. It _should_ still work if you enable verbose gcode output.

This will probably break if the travel speed set in SuperSlicer itself is identical to any first layer
extrusion speeds (unlikely) because it will omit redundant G1 F parameters.

This could be refactored to be able to apply any transformer function to an arbitrary layer

This does not function correctly if "Complete individual objects" is enabled, because it doesn't handle
the resulting multiple "first layers."
"""

from os import environ, replace
from pathlib import Path
from sys import argv
from tempfile import NamedTemporaryFile

def main(argv=argv):
    first_layer_accel = environ['SLIC3R_FIRST_LAYER_ACCELERATION']
    travel_speed = 60 * int(environ["SLIC3R_TRAVEL_SPEED"]) # G1 moves speeds are in mm per minute
    new_first_layer_travel_speed = 60 * int(argv[-2])
    input_gcode_filename = argv[-1]

    def adjust_speed_if_travel_move(line: str) -> str:
        # for matching purposes, strip whitespace and any comment
        trimmed = line.split(";", 1)[0].strip()

        if (
            (trimmed.startswith("G1 ") or trimmed.startswith("G0 "))
            and trimmed.endswith(f"F{travel_speed}")
            and ("Y" in trimmed or "X" in trimmed)
            and "E" not in trimmed
        ):
            return line.replace(f"F{travel_speed}", f"F{new_first_layer_travel_speed}")

        if trimmed.startswith("SET_ACCEL") or trimmed.startswith("M204"):
            return f";{line}"

        return line

    with NamedTemporaryFile(
        mode="w+t",
        prefix="limit_first_layer_travel_speed_output",
        dir=str(Path(input_gcode_filename).parent),
        delete=False,
    ) as temp_gcode:
        temp_gcode_filename = temp_gcode.name
        
        with open(input_gcode_filename) as input_gcode:
            acceleration_lines = [
                f"M204 S{environ['SLIC3R_DEFAULT_ACCELERATION']} ; explicitly set default acceleration in case I fubarred something\n"
            ]
            
            # pass through unchanged all the lines until the first ';LAYER_CHANGE'
            for line in input_gcode:
                temp_gcode.write(line)

                if line.startswith("SET_ACCEL") or line.startswith("M204"):
                    acceleration_lines.append(line)

                if line == ";LAYER_CHANGE\n":
                    break

            # ensure that the first layer acceleration is set even though all following
            # acceleration limits will be elided until the second layer
            temp_gcode.write(f"M204 S{first_layer_accel}\n")

            # now we're in the first layer, until we hit the next ';LAYER_CHANGE'
            for line in input_gcode:
                temp_gcode.write(adjust_speed_if_travel_move(line))

                if line.startswith("SET_ACCEL") or line.startswith("M204"):
                    acceleration_lines.append(line)

                if line == ";LAYER_CHANGE\n":
                    break

            # Replay all of the bundled up first layer acceleration limit adjustments,
            # assuming that the machine limits configured during the first layer
            # cummulatively will yield the same state as long as their order is retained 
            temp_gcode.writelines(acceleration_lines)

            # pass the rest of the lines through unchanged
            for line in input_gcode:
                temp_gcode.write(line)

            # add final comment lines stating that we rewrote first layer travel moves and acceleration limits
            temp_gcode.write(
                f"; first layer travel moves changed from {travel_speed} to {new_first_layer_travel_speed}\n"
                f"; first layer accelerations limited to {first_layer_accel}\n"
            )
        
        # close, then move using os.replace (NOT rename)
        temp_gcode.close()
        replace(temp_gcode_filename, input_gcode_filename)

if __name__ == "__main__":
    main()

Thank you, very helpful!!