Creating a Single-Sprite Variant

A single-sprite asset-generation test case (asset_kind = "sprite", the default) draws one sprite onto the whole canvas to match a written brief — there is no target image. Its version offers one or more variants, and a run selects exactly one. Every variant seeds the version’s common specs (the brief) 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 full procedure for adding a variant to an existing single-sprite asset-generation version. The authoritative rules live in Manifests; read them first.

For a sprite-sheet case (asset_kind = "sprite-sheet") — one whose [sheet] table declares a set of animation frames, each a separate file — see Creating a Sprite-Sheet Variant instead, where a variant also varies only the brief against the shared [sheet] frames and named sequences. To author a brand-new case, see Authoring an Asset-Generation Test Case. To add a mode to an end-to-end case instead, see Creating an End-to-End Variant.

What a single-sprite variant can (and cannot) change

This is the one place asset-generation variants differ sharply from end-to-end ones. An asset-generation case has no target image and declares no [[reference]] — resolution rejects any reference, common or per-variant. A variant therefore has nothing to repoint: the model draws to match the brief, not to copy a supplied picture.

What a variant can do is vary the brief the model draws toward, via an additive spec: a tighter palette, a stricter operation budget, a required drawing technique (flat fills only; no dithering), or a different stylistic constraint. If you need a genuinely different subject, that is a new case, not a variant.

A variant’s spec entries are additive — they layer on top of the common ones rather than replacing them. A variant adds no review items, because an asset-generation case has no reviewer checklist at all: the sprite 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). So the variant brief is the only place its constraint is recorded — 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 (e.g. flat);
• display name — title case, the variant’s name (e.g. Flat Shading);
• description — one line naming the constraint, since there is no menu label to carry it.

Favor a single constraint a reviewer can observe in the regenerated sprite.

2. Write the variant brief

Create specs/<slug>.md, stated as a delta against the common brief (“same subject, silhouette, and palette as the brief, except …”):

• open by stating it builds on the common brief, by name;
• state the added or tightened constraint with precise, testable terms (exact colors, an operation cap, the technique required);
• reaffirm that it draws to match the same brief — the subject does not change, only the added constraint does.

A variant spec may reference the common specs freely (they are always seeded) but must not 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, so the brief spec just names its source:

variants/flat.toml

slug = "flat"
name = "Flat Shading"
description = "Same brief, drawn with flat fills only — no gradients or dithering."
spec = [{ source = "specs/flat.md" }]

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

Rules enforced at resolution:

• spec entries are additive on the common specs; within one variant, no two seeded specs (common + own) may share a dest.
• No reference entry — references are rejected for this test type entirely (an asset-generation case has no target image), so neither the case nor a variant may declare one.
• No review_item entries — an asset-generation case declares no reviewer checklist, on the case or on a variant.

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

Validate your work

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 lint the specs with npm run lint:specs (markdownlint + cspell; see Building). Then exercise it with Run a Test Case — a backend that already holds this version keeps serving the old definition until you force a re-ingest, so re-ingest the case after adding the variant (see Running the Local Service Stack).