Creating a Mesh Model Variant

Overview

A static meshed asset-generation test case (asset_kind = "mc-model", "sn-model", or "dc-model") sculpts one 3D model by compositing a continuous signed-distance field with a meshing binary, which extracts a triangle mesh, toward a goal described in a brief. Its version offers one or more variants, and a run selects exactly one. Every variant seeds the version’s common specs plus its own additive specs. The chosen variant’s slug is recorded in the run record, so every result is attributed to a specific build.

This guide is the procedure for adding a variant to an existing static-meshed version. The authoritative rules live in Voxel cases, the tool interface in Mesh binaries, and the Manifests overview.

For a rigged meshed case (any -animation kind) see Creating a Mesh Animation Variant.

Variant scope

An asset-generation case has no target model and declares no [[reference]]; resolution rejects any reference, common or per-variant. The model is human-reviewed against the brief, so a variant has no target to repoint.

A variant varies two things:

• the brief the model sculpts toward, through an additive spec: a tighter palette, a stricter budget of primitives or CSG operations, a required technique such as symmetry via the mirror op, hard unions with no --blend, or mandatory --sharp on armor edges for a dc case, or another observable stylistic constraint in the extracted mesh;
• the field bounds, by declaring its own [voxel] table. A variant’s [voxel] replaces the case’s for runs of that variant, so one case can offer the same subject at several sizes. A variant with no [voxel] inherits the case’s bounds.

The asset_kind is version-level, and it fixes both the meshing binary and its surface character: an mc low-poly, sn smooth, or dc sharp mesh. A variant cannot switch it or turn a static model into an animation. A genuinely different subject is a new case or a new version rather than a variant.

An asset-generation case declares no reviewer checklist. The model is judged as a whole against the brief it was seeded with, on the case’s single overall domain (see Judged on one overall rating). The variant brief is therefore the only place its constraint is recorded, so write it precisely enough that a reviewer can weigh it.

Procedure

1. Choose the variation

Decide the constraint the variant imposes and keep it consistent everywhere:

• slug, lowercase, used in test-case.toml and the spec filename, such as symmetric;
• display name, title case, the variant’s name, such as Mirror-Symmetric;
• description, one line naming the constraint.

Favor a single constraint a reviewer can observe in the extracted mesh, either rotating in the 3D viewer or in the rendered preview.

2. Write the variant brief

Create specs/<slug>.md, stated as a delta against the common brief:

• open by stating which common brief it builds on, by name;
• state the added or tightened constraint in precise, testable terms: exact colors, an operation cap, the CSG technique required;
• reaffirm that it sculpts toward the same brief with the same meshing binary, with only the added constraint changing.

A spec whose source ends in .hbs is rendered per run and may read {{voxel.width}}, {{voxel.height}}, and {{voxel.depth}}, so a brief that states its bounds reads correctly at every size variant.

A variant spec may reference the common specs freely, since they are always seeded, and must never reference another variant’s spec.

3. Create the variant file and list it

Write variants/<slug>.toml as a standalone TOML document whose top-level keys are the variant’s fields, then add its path to the variants array in test-case.toml. The first entry is the default. Paths inside resolve against the version folder, and dest defaults to source.

variants/symmetric.toml

slug = "symmetric"
name = "Mirror-Symmetric"
description = "Same subject and mesher, built left/right symmetric with mirror."
spec = [{ source = "specs/symmetric.md" }]

# test-case.toml: add the new file to the ordered list (first = default)
variants = ["variants/base.toml", "variants/symmetric.toml"]

What resolution enforces, and what a variant leaves alone:

• spec entries are additive on the common specs. Within one variant, no two seeded specs may share a dest.
• A reference entry is rejected for this test type, on the case and on a variant.
• A variant’s [voxel], when declared, is validated exactly as the case’s.
• asset_kind is version-level, so a variant declares none and cannot switch the meshing binary.
• A variant declares no review items, matching the case.

Update the human-readable comment in the manifest that enumerates the variants so the list stays accurate.

Validate your work

From the repository root, lint the specs:

npm run lint:specs   # markdownlint-cli2 + cspell over test-cases/**

If cspell flags a legitimate domain term, add it to .cspell/project-words.txt rather than rewording good prose to dodge the dictionary.

Seed and render the new variant, and re-check the existing ones to confirm your edits changed nothing for them:

tcab seed   --test-case <slug> --version <version> --variant <new-variant>
tcab prompt --test-case <slug> --version <version> --variant <new-variant>

Read the seeded output to confirm the new variant’s brief is self-contained and that its effective bounds and meshing binary are the ones you intended.

The backend’s definition store is immutable per case version, so force a re-ingest before running:

scripts/reingest.sh --force <slug>

Force re-ingest overwrites the stored version in place and is for development only. Adding a variant edits an existing version, so do it only while that version is unpublished; a version a published run references is frozen and needs a new version instead. Then exercise the variant with Run a Test Case.