[wyongzhi]

What was the problem/requirement? (What/Why)

DefaultMaxHandler.set_scene_file calls rt.loadMaxFile(file_path, quiet=True) without useFileUnits. The MAXScript default is useFileUnits:false, which rescales the scene to the current system units, regardless of the "Respect System Units in Files" preference. Workers run 3ds Max under a fresh profile whose system unit is inches, so any scene authored in another unit is silently rescaled on load.

Uniformly scaled geometry renders the same, but modifier parameters stored in absolute units do not scale with it. A customer scene authored in centimetres rendered a Normalize Spline + Sweep terrain with a different shape and a Path Deform train at the wrong height on Deadline Cloud, while rendering correctly on their on-prem farm. Nothing in the adaptor logged units, so there was no diagnostic trail.

What was the solution? (How)

• rt.loadMaxFile(file_path, quiet=True, useFileUnits=True), so the session adopts the file's units. Per Autodesk docs this does not modify 3dsmax.ini.
• Log units.SystemType / units.SystemScale before and after load. The log is best-effort: a failure to read units is a warning and never affects the load or path mapping.
• Regenerated test/integ/test_scripts/batch_render_test/expected_images. BatchRenderTest2024.max is authored in centimetres (every other integ scene is in inches), so its golden images had been rendered from the rescaled scene. With the fix the scene renders at file scale and the images change: with_state_000 differs in 76% of pixels, the six with_override_* frames in 20%, cam_only_000 and with_preset_000 are unchanged within JPEG noise.

Scope: the 3dsmaxbatch/3dsmax adaptor path only. The 3dsmaxcmd submitter renders via 3dsmaxcmd.exe and the V-Ray standalone submitter exports a .vrscene; neither loads a .max file through this handler. job_bundle_output_test_runner.py also calls loadMaxFile but is a local submitter test tool, left unchanged.

What is the impact of this change?

Behaviour change: scenes whose file units differ from the worker's system units now render at file scale, matching interactive 3ds Max. Previously they were rescaled to the worker's units. Scenes authored in inches are unaffected.

How was this change tested?

Unit tests, hatch run all:test (py3.10, 3.11, 3.12): 483 passed each. hatch run lint clean.

• loadMaxFile is called with quiet=True, useFileUnits=True
• units are logged before and after load
• a failing units read still loads the scene, still runs path mapping, and emits a warning instead of raising

Integration tests, pytest test/integ -m adaptor on a Windows g5 workstation with 3ds Max 2026 and V-Ray 7: 7 passed, 1 xfailed (pre-existing), 2 failed for environment reasons unrelated to this change (lightmix needs V-Ray GPU and the headless session had no GPU device; vrmesh_path_remap fails identically on unmodified mainline on this machine). test_batch_render_adaptor passes with the regenerated images and fails without them.

Direct verification on the same 3ds Max 2026 (fresh profile, inches) from work station. Scene authored in cm: spline + Normalize Spline (seg length 20) + Sweep terrain, Box + Path Deform train, measured at frame 7:

	authored (cm)	useFileUnits:false (before)	useFileUnits:true (after)
session units after load	cm	inches	cm
Terrain verts / faces	1417 / 2830	923 / 1842	1417 / 2830
Terrain bbox Z range	-492 .. 633	-2.9 .. 38.5	-492 .. 633
TrackPath X extent	2000	787.4 (= 2000 / 2.54)	2000

With useFileUnits:false the vertex count changes, so the terrain is reshaped, not just scaled. With useFileUnits:true every measurement matches the authored scene.

Was this change documented?

Commit message / changelog entry. No user-facing docs change needed.

Did you modify schema files?

• Yes
• No

Is this a breaking change?

No. Output for unit-mismatched scenes changes to match interactive 3ds Max; that is the fix.

[github-actions]

Claude review · advisory

Reviewed 037766c (changes since 2a8bc34): 0 new, 0 resolved.

Open: 0 blocking · 0 should-fix · 0 nit. ✅ Nothing blocking.

_{Fix or reply to each thread; the next revision's review re-checks open threads and resolves those it agrees are handled. Resolving a thread yourself also closes it. Later revisions review only what changed.}

[seant-aws]

double checking, do we need changes with cross component tests with this test change ? I think no right, the units should remain the same for those tests..

[wyongzhi]

double checking, do we need changes with cross component tests with this test change ? I think no right, the units should remain the same for those tests..

Right, there's no need to change the cross component tests. Scanned the file units of every scene under test/integ/test_scripts on 3ds Max 2026: BatchRenderTest2024.max is the only one authored in cm, all the others (minimal_test, lightmix, re_enabled_test, re_disabled_test, vray_re_test, vray_vrmesh_remap_test) are inches, same as the worker default, so loading them with useFileUnits=True changes nothing. The other 7 adaptor integ tests passed unchanged on the same machine.