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Create a Sprite-Sheet Variant

Add a new variant to an existing sprite-sheet asset-generation version (asset_kind = "sprite-sheet" — a [sheet] of frames, each a separate file). The full procedure is in Creating a Sprite-Sheet Variant.

The key constraint: an asset-generation case declares no references at all (resolution rejects any, common or per-variant) and forbids per-variant [sheet] tables. There is no target image — a variant varies only the brief (an additive spec) the model draws toward: a tighter palette, a stricter operation budget, an added stylistic rule. The [sheet] frames and named sequences are version-level too — a variant shares them and cannot redeclare them, and review stays per frame (the sequences only drive the review UI’s animated playback).

For a single-sprite case (asset_kind = "sprite") instead? See Create a Single-Sprite Variant. Adding a mode to an end-to-end case? See Create an End-to-End Variant.

Steps

Section titled “Steps”
  1. Choose a consistent slug (e.g. flat) and display name (e.g. Flat Shading) describing the drawing constraint it imposes.
  2. Write specs/<slug>.md: an additive brief stated as a delta against the common brief (“same subject, frames, and palette, except …”), with precise, testable constraints, saying whether each applies to every frame, a named sequence, or across frames. It may reference the common specs but not another variant’s spec, and it draws toward the same [sheet] layout.
  3. Create variants/<slug>.toml (a standalone TOML file whose top-level keys are the variant’s fields; dest defaults to source) and add its path to the variants list in test-case.toml. Do not add a [sheet] table — it is declared once at the version level:
variants/flat.toml
slug = "flat"
name = "Flat Shading"
description = "Same brief, drawn with flat fills only — no gradients or dithering, across every frame."
spec = [{ source = "specs/flat.md" }]

spec entries are additive on the common specs; within one variant no two seeded specs may share a dest. A variant declares no review_items — an asset-generation case has no reviewer checklist. Do not add a reference (resolution rejects a variant-specific reference for this test type) or a per-variant [sheet] / asset_kind.

Validate

Section titled “Validate”
Terminal window
tcab seed   --test-case <slug> --version <version> --variant <new-variant>
tcab prompt --test-case <slug> --version <version> --variant <new-variant>

Seed and render the new variant and re-check the existing ones to confirm nothing else changed and the brief still resolves self-contained, leaving the [sheet] frames and sequences intact.