Klipper GCode Preprocessor for Object Cancellation

This is a Rust port of the excellent preprocess-cancellation preprocessor by Frank Tackitt. The preprocessor modifies GCode files to add Klipper's exclude object gcode.

The following slicers are currently supported:

SuperSlicer
PrusaSlicer
Orcaslicer
Slic3r
Cura
IdeaMaker

Why the rewrite

The SBCs typically running Klipper are not very beefy and when uploading GCode files that are 100+ MB large the upload often times out during preprocessing of the files. This rewrite tries to solve that problem and keep the convenience of having files automatically processed on the host without having to deal with Slicer integration.

Testing on an M1 Macbook shows a 10x improvement in processing speed, from 48s down to <5s for a reasonably complex file of about 130MB.

time preprocess_cancellation-macos  demo/plate_1.gcode
preprocess_cancellation-macos   32.57s user 1.55s system 70% cpu 48.234 total

preprocess-cancellation-rs   3.85s user 0.13s system 93% cpu 4.276 total

Installation and usage

SuperSlicer, PrusaSlicer, and Slic3r

Download the provided binary for your platform, and place it in with in your slicer's folder.

In your Print Settings, under Output Options, add preprocess_cancellation.exe; to the "Post-Processing Scripts". For mac or linux, you should just use preprocess_cancellation;

Then, all generated gcode should be automatically processed and rewritten to support cancellation.

G-Codes for Object Cancellation

There are 3 gcodes inserted in the files automatically, and 4 more used to control the object cancellation.

EXCLUDE_OBJECT_DEFINE NAME=<object name> [CENTER=x,y] [POLYGON=[[x,y],...]]

The NAME must be unique and consistent throughout the file. CENTER is the center location for the mesh, used to show on interfaces where and object being canceled is on the bed. POLYGON is a series of points, used to represent the bounds of the object. It can be just a bounding box, a simplified outline, or another useful shape.

EXCLUDE_OBJECT_START NAME=<object name> and EXCLUDE_OBJECT_END [NAME=<object name>]

The beginning and end markers for the gcode for a single object. When an object is excluded, anything between these markers is ignored.

For a full breakdown, see the klipper G-Code Reference

Known Limitations

Cura and Ideamaker sliced files have all support material as a single non-mesh entity. This means that when canceling an object, it's support will still print. Including support that is inside or built onto the canceled mesh. The Slic3r family (including PrusaSlicer and SuperSlicer) treat support as part of the individual mesh's object, so canceling a mesh cancels it's support as well.

How does it work

This looks for known markers inside the GCode, specific to each slicer. It uses those to figure out the printing object's name, and track all extrusion moves within its print movements. Those are used to calculate a minimal bounding box for each mesh. A series of EXCLUDE_OBJECT_DEFINE gcodes are placed in a header, including the bounding boxes and objects centers. Then, these markers are used to place EXCLUDE_OBJECT_START and EXCLUDE_OBJECT_END gcodes in the file surrounding each set of extrusions for that object.