scenario-blender-retopology
Blender retopology
Expert retopology is a plan executed with the fewest loops that capture the forms and let the mesh deform: loops close around eyes, mouth and joints, poles sit where nothing moves, and the subdivided surface, not the cage, matches the sculpt. An agent without a mouse can build every piece of this from data, but it reaches expert quality only on the parts it plans explicitly. Automatic remeshing is a finish for static assets and a start for everything else. If a sibling skill named here is missing from your available skills, ask the user to install it (npx skills add scenario-labs/skills --skill <name>); unattended, proceed from tool schemas and flag the gap.
REQUIRED BACKGROUND: scenario-blender-expert (execution channel, review loop, 5.2 API changes). Toolkit: scripts/bx_retopo.py (import sys; sys.path.append("<skills>/scenario-blender-retopology/scripts"); import bx_retopo as R), all coordinates in the sculpt's local space.
Stance (the expert delta)
- Map first, as data. Kaspar draws six layers on the sculpt before any vertex: edge flow, primary creases, secondary (expression-only) creases, articulation, expression bounds, landmarks (BCON22 [00:07:55], shown in frames 00:07:53 to 00:14:38). The agent writes the same map as coordinates and loop counts (landmarks from renders plus
R.surface_point), then builds. - Loops are the budget, not vertices. Articulation minimum (Kaspar after Brian Tindall): lids, lips and brows as curves with 3 controls and 2 handle loops each, plus 2 corner loops on eyes; upper count = lower count (Dikko, Kaspar, Kenny); 3 loops per joint; a crease is 1 loop on it plus 2 hugging it. Elsewhere "as much as it needs to be" (Kaspar Live #3 [01:56:33]).
- Poles: valence 3 or 5, where nothing moves, never on a crease loop, a shell rim or the face center line (Kaspar Live #7 [00:11:41], Live #3 [00:36:54]; Dikko [00:04:49]). Lampel's reason: pinching is a density jump in the subdivided result, harmless on flat still areas (BCON24 [00:21:18]). [added] An agent's poles come from ring-count reductions (4 per unit) and from cut borders that staircase across an auto base (about half their vertices): budget both.
- Loops close on themselves. A spiral around eyes or lips means rebuild (Dikko); a spiral that terminates in a still area is tolerated (Dikko body [00:09:34], Kaspar nose).
- Judge the subdivided surface. A snapped cage shrinks inside when subdivided; a Shrinkwrap offset fixes convex areas and worsens cavities. Fit the cage so its subdivided surface matches (Duha BCON23 [00:08:58]):
R.fit_subdiv. Kaspar's Multires Apply Base does the same job but overshoots (measured below). - Game low poly = silhouette plus animation loops (SpeedChar): face about 3x body density, triangles wherever nothing bends, twisted quads cut by hand so baker and engine agree, low poly slightly proud of the high; every hard edge is a UV seam (On Mars 3D).
- Auto-remesh fits static, scanned, background or bake-only assets (Lampel [00:09:05], Grant Abbitt, Duha, Jamie Dunbar). For deforming characters it lacks the judgment calls: on the sheep, QuadriFlow at expert density gave no rings around eyes or mouth and tore a thin ear.