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S01 Modeling — Stage brief (pilot)

  • Date: 2026-10-07 · Status: draft for owner review
  • Blender: 5.2.2 LTS
  • Built from:
  • Evidence level: L1 (documented and traced in source). Nothing here has been changed or benchmarked yet. The runtime probes are listed in §8.

1. What modelling is, as professionals do it

Section titled “1. What modelling is, as professionals do it”

Blender Studio models in eight stages. Each stage is built for the next one.

Stage Hard-surface prop Organic character
Reference and design Real dimensions, blueprints Hand-off from the design sculpt (T-pose, hero pose, deformation tests)
Setup → blocking Low cage plus live modifiers: Mirror, Solidify, Bevel, Array, Edge Split, Boolean Sculpt with voxel remesh / dyntopo, symmetry
Movement test / design check Collections, instances, shape keys Expression and pose tests
Refinement / retopology Selective apply, retopo where needed, small detail Manual retopology over the sculpt (annotate loops, snap, Poly Build), then Multires reprojection
UV hand-over Seams follow topology, unwrap, minimise stretch Same
Delivery and hand-off 10-item cleanup checklist, naming, Asset Pipeline publish, review in Kitsu (the production-tracking tool), hand-off to rigging and shading Same

The census agrees with the docs:

  • The authored artefact is a live recipe, not a final mesh.
    • 91% of mesh objects in asset files carry modifiers.
    • Subdivision Surface alone is 54% of all modifiers.
    • The median mesh has only 111 vertices.
  • The topology rules are real. 94.5% of faces are quads and 0.1% are ngons.
  • Geometry Nodes (GN, Blender’s node-based geometry system) is production infrastructure. There are 836 GN modifiers in asset files and 8,423 in shot files.
  • Bias: the sample is stylised animated film, so hard-surface is under-represented.

2. What survives: the essential maths and data

Section titled “2. What survives: the essential maths and data”
Asset Where Why it survives
SoA Mesh with generic named attributes blenkernel mesh, geometry:: The stable, attribute-generic layer. Upstream finished the migration in 2026, and new algorithms land here (GN Mesh Bevel, merge, triangulate).
BMesh topology kernel bmesh/ Euler operators: each is valid by construction, has an inverse, and costs time proportional to local detail. 83 bmops with typed slots already form an internal command vocabulary.
Core algorithms BM_mesh_bevel, BM_mesh_decimate_*, BKE_mesh_remesh_voxel, BM_mesh_boolean, … The modifier and the operator often call the same function. Imperative vs declarative is a split at the wrapper, not the algorithm.
The modifier stack / GN trees modifiers/, nodes/ Already the professional’s primary artefact, and declarative, reviewable and diffable (nodes-as-code via nodebpy).
Topology and UV conventions Studio docs, census Quads, edge flow, seams as attributes (uv_seam, sharp_edge): checkable rules, not taste.

3. What goes: the ceremony

Section titled “3. What goes: the ceremony”
Ceremony Evidence Dead fact
Modes. Edit mode is a human session: a hidden BMesh copy, synced back only on mode exit. 178/320 operators are gated by mode alone. mode_set dispatches another operator by name. In edit mode Mesh is stale until exit. Conversion cost was reduced but never removed. DF1
Selection as scope. Select, then act. 56 cards proposed remove. loop_select’s exec is already index-driven, but its poll demands a 3D view. DF1
The modal veneer. Drag to set a value. 51 of 66 modal operators also have exec. Bevel’s modal loop restores a snapshot and re-runs the whole operation on every mouse move. DF1, DF3
Polls that encode where the button lives Polls describe the UI location, not what the function needs (loop_select, transform, loopcut). The name heuristic was wrong for 50%. DF2
Hidden context defaults Exec reads the 3D cursor (bisect plane), the view axis (extrude_repeat), tool settings (bevel profile), and local view (multi-object filter). DF2
Status instead of result Operators return FINISHED/CANCELLED. The new geometry is seen by drawing it. DF4
Snapshot undo Every edit-mesh undo step stores a full BMesh→Mesh copy. Python calls push no undo at all by default. DF1
Eye-based QA Face Orientation, overlays, “inspect from different angles”. Only doubles, manifold and applied scale are numeric today. DF4

4. Numbers

Section titled “4. Numbers”
Measure Value
Operators in Blender 5.2.2 2,498 (2,210 C++, 288 Python)
Fail headless poll in every mode (factory scene) 1,605 (64%), all categories
Modelling operators studied 320
…pass poll headless given the right mode/data 270 (84%)
…truly need a GUI 50 (16%): 23 need a region, 27 need an event stream
…modal / no exec 66 / 26
Geometry-changing operators with a declarative twin 125 of 184 (68%): 55 exact, 70 approximate
No twin: “local topology surgery” 59 (dissolve, fill, bridge, knife, loopcut, rip, polybuild, connect, slide, poke, …)

5. Verdicts (proposed, 320 cards)

Section titled “5. Verdicts (proposed, 320 cards)”
Verdict Count Meaning
declare 124 Express as a declared outcome (modifier / GN node) that already exists. 70 need a parity check first.
free 73 (3 contested) Real logic trapped behind mode/selection/GUI. Make it a typed function over explicit inputs that returns a diff.
keep 67 Usable as a function today: stack management, object-level data ops.
remove 56 Ceremony: selection state, mode switches, menus.

44 cards link back to workflow-script rows, so the human path and the code path meet on them.

6. The agent-native shape for modelling (proposal, interpretation)

Section titled “6. The agent-native shape for modelling (proposal, interpretation)”
  1. One source of truth. SoA Mesh is canonical. BMesh becomes an explicit, scoped editing session: open(mesh) → edits → flush() → diff. There is no “mode” and no implicit sync.
  2. Three verb families.
    • Declare: add, edit and reorder modifier / GN steps. This is the primary artefact, stored as code.
    • Edit: typed topology functions over explicit element sets (indices or attribute masks). They are generated from the bmop slot schema and the geometry:: functions.
    • Commit: apply or bake a declared step into data.
  3. Explicit inputs. Every hidden default (cursor, view axis, tool settings, local view) becomes a parameter. Preconditions are declared machine-readably, not inferred from polls.
  4. Results, not statuses. Every call returns a diff (elements created, deleted, changed) plus validity checks. A mesh-isomorphism compare (mesh_comparison exists upstream) is the reference check.
  5. Transactions. Undo and branching are built from Euler-operator inverses (differential), not whole-mesh snapshots.
  6. Placement becomes data. Knife → a cut path or plane. Poly Build / retopology → target loops or patches. Brush → a declared deformation field or 3D path. No headless shim that fakes a mouse.
  7. Machine QA gates. Quad ratio, ngons, manifold, doubles, normals consistency, applied scale and naming run as checks on every commit. That replaces the eye for everything except taste.

7. Needs the owner (contested)

Section titled “7. Needs the owner (contested)”
Card Question
sculpt.brush_stroke Should an agent sculpt by strokes at all, or only by declared fields? This is gray zone G1 (human-like 3D action).
mesh.polybuild_* (retopology) The Studio says final retopology must be manual. Rigging accepts “messy automatic retopo” for previz. Is machine retopology acceptable for final topology?
object.quadriflow_remesh Same question, for the automatic remesher.

8. Open questions and next probes

Section titled “8. Open questions and next probes”
  • Runtime probes (cheap, I can run them):
    • Does temp_override(area, region) make the 23 gui-region operators work in -b?
    • Can a brush stroke be replayed headless?
    • Do Python calls really push no undo step?
    • Result parity of “exact” twins with different implementations (Solidify, Smooth, GN Extrude/Subdivide) via an isomorphism test.
  • Census v2: applied scale, duplicate vertices, flipped normals, naming compliance, UDIMs, pivot Empties. Also explain the 2,606 NodeUndefined nodes.
  • Corpus gap: add a hard-surface / archviz set before ruling on bevel/boolean/array usage.
  • Node tools: enumerate the essentials node tools in 5.2. They are registered per asset and missing from the registry dump. Do any cover the 59 no-twin operators?
  • Upstream: will GN Mesh Bevel replace BM_mesh_bevel? Two bevel implementations exist today.

9. Pilot retrospective: tune before fanning out to other stages

Section titled “9. Pilot retrospective: tune before fanning out to other stages”
What happened Change for the next stages
The name-based gate heuristic was wrong for 50% Pass 3 must read poll bodies. Keep the heuristic only as triage.
The static scan missed transform operators and macros Extend scan_source.py for constant idnames and macros, so the registry and the scan agree.
The workflow script cites keys, not operator ids, so the step→operator map was done by hand afterwards Pass 1 records the operator id for each step (from the keymap file).
The census sample is biased toward one studio style Each stage names a counter-corpus up front.
Pass 3 is the expensive pass (~19 min, ~300k tokens) Split it into parallel trace agents by operator family.
Cards are per operator, but many operators span stages Cards live in the shared docs/discovery/capabilities/. Later stages add human rows and re-verdict.