--downward-settings

--downward-settings supplies the explicit list of machine preset JSON files that the engine uses when performing a downward compatibility check, activated by the companion flag --downward-check. The value is a single quoted string containing one or more absolute file paths separated by semicolons. The option type is a string list with an empty default, meaning it is optional even when --downward-check is set.

Each file in the list must be a system machine preset: the engine reads config_type and config_from from the JSON and immediately aborts with a config-file error if either field is not "machine" and "system" respectively. Non-system or process/filament presets are not accepted. From each valid file the engine reads printable_area, printable_height, bed_exclude_area, and wrapping_exclude_area to derive the effective build envelope. For multi-extruder machines it also reads extruder_printable_area and extruder_printable_height to compute the intersection of all tool heads' reachable zones, storing that as a shared width, depth, and height used in a separate intersection check. Additionally, the engine reads extruder_clearance_height_to_lid, extruder_clearance_height_to_rod, extruder_clearance_max_radius, and extruder_clearance_dist_to_rod unconditionally from every machine preset; these values are held and applied only when a plate is in one-at-a-time (sequence) print mode.

For plates in sequence mode, the engine first evaluates the four clearance parameters. If all four are present and non-zero in the candidate machine preset, the engine compares them against the clearance values encoded in the loaded 3MF; a mismatch marks the machine incompatible immediately for that plate. If any of the four clearance fields is missing or zero in the preset, the machine is also immediately marked incompatible for that plate with no fallback. When the clearance check passes, the standard bounding-box test against the machine's printable dimensions still runs afterward; it is not skipped. For plates that are not in sequence mode only the bounding-box test runs.

When --downward-settings is omitted entirely but --downward-check is active, the engine falls back to its bundled cli_config.json resource file, which maps the current printer model and system name to a list of older preset names, then resolves those names from the bundled machine_full/ resource directory. This means the fallback only works for first-party (BBL) printer families whose downward mapping is encoded in the shipped resources; any other printer model produces an empty check list and the check is effectively skipped. Supplying --downward-settings explicitly bypasses this lookup and lets you specify any system machine preset regardless of vendor or bundled mapping.

After testing each candidate machine against every plate's object bounding box (and clearance envelope where applicable), the engine writes passing machine names as a JSON array under the key "downward_compatible_machine" in result.json. The key is omitted entirely if no candidates pass. Machines that fail are also removed from the "upward_compatible_machine" list if they appear there, so a single incompatible candidate can affect both output fields simultaneously. The check is purely geometric -- no G-code is generated as part of it.