gn-zone-iterate

Geometry Nodes zone iterate

A Repeat Zone row and a For Each Element tower that witness geometry-nodes-python zone pairing — not tree structure.

pair_with_output is load-bearing. Unpaired Repeat Input has no Geometry sockets; unpaired For Each evaluates empty (Cannot evaluate node group on 4.5). For Each's main Geometry output is the input mesh passthrough; generated cubes live on Generation_0.

Closed forms (cube = 8 verts / 6 faces):

• Repeat: join one translated cube per iteration. verts = 8 × (1 + N) with N=3 → 32. X-centers at k × 1.2 for k = 0..3.
• For Each: one cube per POINT, Z-offset by Index × 0.6. verts = 8 × P with P=6 → 48. Z-centers at i × 0.6 + 0.21.

Count alone is not enough. Joining N+1 cubes at the origin hits 32 verts with a single X-center (--no-offset). The center axis is the second witness.

Same on 4.5 LTS and 5.x (zones are 4.3+). No skip.

What failure each check would catch:

• exit 3 — Repeat pairing broken or iterations wrong (--unpair-repeat → 0/0; --repeat-iterations 1 → 16/12)
• exit 4 — Repeat count matches but cubes collapsed (--no-offset)
• exit 5 — For Each pairing broken, element count wrong, or main-socket passthrough (--unpair-foreach → 0/0; --foreach-count 3 → 24/18; --foreach-main → 6/0)
• exit 6 — For Each count matches but Z-centers do not

Run

blender --background --python gn_zone_iterate.py --
blender --background --python gn_zone_iterate.py -- --output zones.png

The --output render path measures framing via examples/gallery_framing.py (exit 10 on violation).

Staging. Everything presentational runs after check() has passed on the raw evaluated zones. Each zone's blocks are graded along the axis the zone iterates on, using Object-space coordinates (amber to red along X for the four Repeat blocks, deep teal to mint along Z for the six For Each blocks), so the colour steps count the iterations. A render-only Bevel modifier after the GN modifier chamfers the cubes into machined blocks. The Repeat row sits on a walnut plinth; the For Each tower is threaded on a steel spindle over a round walnut base, so its 0.18 m gaps read as spacing on a rod rather than floating cubes.

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 carrier mesh was rewritten
3	Repeat evaluated vert/face count off closed form
4	Repeat X-centers off closed form
5	For Each evaluated vert/face count off closed form
6	For Each Z-centers off closed form
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, --no-offset, --unpair-foreach, or --unpair-repeat.