usd-export-evaluation-mode

USD export evaluation_mode

A SUBSURF cube exported through wm.usd_export that witnesses evaluation_mode='RENDER' against 'VIEWPORT' — the contract usd-export-evaluation-mode.py names but does not prove.

Catmull-Clark on a cube is closed form: verts = 2 + 6 × 4^n (n=1 → 26, n=2 → 98). TESSELLATE + VIEWPORT writes 26 points / 24 quads; TESSELLATE + RENDER writes 98 / 96. Default export_subdivision='BEST_MATCH' writes the 8-vert cage plus subdivisionScheme = catmullClark, so evaluation_mode is silent — both files are the cage. TESSELLATE is what makes the mode observable.

The still is numeric-adjacent: left is viewport tessellation (flat-shaded L1), right is render tessellation (smoothed L2). The USDA point counts are the evidence; the two balls depict the two qualities the exporter chooses between.

What failure each check would catch:

• exit 3 — VIEWPORT TESSELLATE did not write the L1 closed form
• exit 4 — RENDER TESSELLATE wrote viewport quality or the BEST_MATCH cage (--evaluation-mode VIEWPORT measured 26/24; --subdivision BEST_MATCH measured 8/6 catmullClark)
• exit 5 — BEST_MATCH stopped writing the cage
• exit 6 — RENDER and VIEWPORT files are identical

Staging: Catmull-Clark pulls the surface inside the 2 m cage, and level 1 and level 2 shrink by different amounts, so both balls used to hover about 0.16 m over the floor at the cage's z = 1.0. The render path now rests each one on the floor from its own evaluated vertices (measured zmin 0.000000 for both), after the check has run.

Probed on the CI Linux portables Blender 5.2.1 LTS (9e2066aef7ef) and Blender 4.5.13 LTS (daeeeca98fb0): wm.usd_export exists, poll() is true in --background, evaluation_mode is {RENDER, VIEWPORT}. The --output render path measures framing via examples/gallery_framing.py (exit 10 on violation).

Run

blender --background --python usd_export_evaluation_mode.py --
blender --background --python usd_export_evaluation_mode.py -- --output u.png

Exit codes

Per-script sequential checks. 9 is a valid check code; there is no rule against it. 10 is the shared framing helper.

Code	Meaning
0	Success
1	Uncaught exception (FATAL wrapper)
2	argparse / usage; also base cube verts ≠ 8
3	VIEWPORT TESSELLATE point/face count off closed form
4	RENDER TESSELLATE point/face count or scheme off closed form
5	BEST_MATCH cage point count or scheme off
6	RENDER and VIEWPORT USDA point counts are identical
10	Gallery framing violation
12	--output produced no file

The blender-smoke workflow runs the check on Blender 5.2 LTS and 4.5 LTS (5.1 on the weekly cron, the needs-5.1 PR label, or manual dispatch). Smoke does not pass --output, --evaluation-mode, or --subdivision.