Imported from tjdrhs90/flutter-flame-harness (skills/flame-harness-design/SKILL.md). Install upstream with npx skills add tjdrhs90/flutter-flame-harness --skill flame-harness-design. Copyright stays with the author.

flame-harness-design

Phase 3 of the flutter-flame-harness pipeline. Reads the latest PRD and config.md, then produces a design document that specifies the lib/ui/design_tokens.dart constants, the game's visual/art concept, and the asset and audio sourcing plan (including launcher icon and splash screen intent). Advances pipeline state to contract.

All file schemas (config.md, state.md, pipeline-log.md) and the phase transition table are defined in docs/harness-protocol.md — refer to that document as the single source of truth (§2 for state.md schema; §7 for the design → contract transition). Do not redefine schemas here.

Input

1. Read docs/harness/config.md

Extract:

If config.md does not exist, abort with: flame-harness-design: docs/harness/config.md not found — run the orchestrator to bootstrap first.

2. Read the latest PRD

Find the most recent file matching docs/harness/plans/*-prd.md (sort descending by filename, take the first). If no PRD exists, abort with: flame-harness-design: no PRD found in docs/harness/plans/ — run flame-harness-plan first.

Extract from the PRD:

• Genre & core mechanic — informs colour mood (e.g., dark sci-fi vs. bright hyper-casual)
• Target age / tone — age rating and energy level of the visual style
• Monetisation hook — AdMob placement type (banner at bottom → affects HUD spacing)
• Win/lose conditions — informs what UI states need distinct visual treatment

Design tokens

Write a specification for lib/ui/design_tokens.dart that a generator phase Claude can implement verbatim as const Dart values. The spec must cover every sub-section below.

Colour palette

Derive a palette from the genre and tone. Use the following template — replace every <...> with a real hex colour and rationale:

Primary       <#RRGGBB>  — main brand / call-to-action colour
PrimaryDark   <#RRGGBB>  — pressed / shadow state of primary
Accent        <#RRGGBB>  — highlights, score text, power-up glows
Background    <#RRGGBB>  — game canvas and screen background
Surface       <#RRGGBB>  — card, dialog, overlay background
OnBackground  <#RRGGBB>  — text / icon colour on background
OnSurface     <#RRGGBB>  — text / icon colour on surface
Error         <#RRGGBB>  — error states, health loss flash

Rules:

• Minimum contrast ratio of 4.5:1 for any text colour against its background.
• Background and Primary must share the same temperature (both warm or both cool).
• Accent must differ from Primary by at least 60° of hue to provide visual pop.
• For dark-themed games (sci-fi, horror) set Background ≤ #333333; for bright hyper-casual games set Background ≥ #E0E0E0.

Typography scale

Specify font family, weight, and size for each role. If the game uses a custom font, name the Google Font and its import path; otherwise default to Roboto.

Display   family: <FontName>  weight: 900  size: 48 sp  — game title on main menu
Heading1  family: <FontName>  weight: 700  size: 32 sp  — screen headings
Heading2  family: <FontName>  weight: 700  size: 24 sp  — section headings, score
Body      family: <FontName>  weight: 400  size: 16 sp  — general UI text
Caption   family: <FontName>  weight: 400  size: 12 sp  — labels, tooltips
Button    family: <FontName>  weight: 600  size: 18 sp  — primary buttons
HUD       family: <FontName>  weight: 700  size: 20 sp  — in-game HUD counters

Use sp (Flutter TextScaler-aware) for all sizes. Game HUD text should use fontFeatures: [FontFeature.tabularFigures()] for score counters.

Spacing scale

Define a base unit and derive the full spacing scale. Typical base is 4 dp:

xs:   4 dp   — tight padding (icon labels)
sm:   8 dp   — inner card padding
md:  16 dp   — standard screen margin
lg:  24 dp   — section gap
xl:  32 dp   — screen top/bottom padding
xxl: 48 dp   — hero area padding

All layout constants in design_tokens.dart use these named values — no raw numbers in UI code. Spacing values are applied as const double fields.

Also define minTapTarget = 48.0 (dp) — every menu/overlay button must be at least this size (accessibility gate R10; pairs with the 4.5:1 contrast rule above).

Radius and elevation

radiusSm:   4 dp   — chip, small badge
radiusMd:   8 dp   — card, dialog
radiusLg:  16 dp   — bottom sheet, hero card
radiusFull: 999 dp — pill buttons

elevationSurface:  2 dp
elevationDialog:   8 dp
elevationFab:     12 dp

design_tokens.dart file template

The generator must emit a file with this exact structure:

// lib/ui/design_tokens.dart
// AUTO-GENERATED by flame-harness-design — do not edit manually.
// See docs/harness/plans/<date>-design.md for rationale.

import 'package:flutter/material.dart';

abstract class DesignTokens {
  // --- Colours ---
  static const Color primary       = Color(0xFF______);
  static const Color primaryDark   = Color(0xFF______);
  static const Color accent        = Color(0xFF______);
  static const Color background    = Color(0xFF______);
  static const Color surface       = Color(0xFF______);
  static const Color onBackground  = Color(0xFF______);
  static const Color onSurface     = Color(0xFF______);
  static const Color error         = Color(0xFF______);

  // --- Spacing ---
  static const double spaceXs  =  4;
  static const double spaceSm  =  8;
  static const double spaceMd  = 16;
  static const double spaceLg  = 24;
  static const double spaceXl  = 32;
  static const double spaceXxl = 48;

  // --- Radius ---
  static const double radiusSm   =   4;
  static const double radiusMd   =   8;
  static const double radiusLg   =  16;
  static const double radiusFull = 999;

  // --- Elevation ---
  static const double elevationSurface = 2;
  static const double elevationDialog  = 8;
  static const double elevationFab     = 12;

  // --- Typography helpers ---
  static const String fontFamily = '______';
}

Fill every ______ from the palette and typography spec written above.

Visual concept

Art direction

Describe the overall visual style in 3–5 sentences covering:

1. Art style — pixel art / vector flat / hand-drawn / 3-D rendered sprites
2. Colour mood — how the palette reinforces the genre's emotional tone
3. World / environment — background theme (city, space, forest, dungeon, etc.)
4. Character / enemy design — silhouette language (cute rounded vs. angular menacing)
5. UI chrome style — whether overlays feel like HUD panels, storybook pages, arcade bezels, etc.

The description must be concrete enough that a sprite artist (or an AI image prompt) could reproduce the style without further guidance.

Sprite list (MVP)

List every sprite needed for the MVP core loop. For each sprite, specify:

Dimensions are in dp at 1× scale; the asset pipeline should export at 1×, 2×, and 3×.

Overlay and HUD layout

Describe the layout of each Flutter overlay:

• Main menu — what elements are visible and their rough positions
• In-game HUD — score, lives/health, pause button placement
• Pause overlay — resume, restart, settings
• Game-over screen — score, best score, restart, AdMob rewarded-ad revival button
• Settings screen — BGM toggle, SFX toggle, language toggle

Each description maps directly to a Flutter widget in lib/screens/ or lib/ui/.

Asset/audio plan

Defaults the generator can always satisfy with no sourcing: audio = code-synthesized (tool/build_audio.dart → WAV); visuals = code-drawn (CustomPainter/Flame shapes from the palette). Specify sprite art below only if the concept needs it — choose CC0 pack or AI; the generator cleans sourced art's background with tool/strip_bg.dart. The harness never depends on art that isn't sourced, so a game can ship fully code-drawn.

Sprite and image assets

State for each visual asset whether it will be:

For every free pack named, provide the pack URL and its license (CC0, CC-BY, etc.). For AI-generated assets, write the exact prompt template to use (substituting <genre> and <style> from the art direction above).

Assets must be declared in pubspec.yaml under flutter: assets:. Provide the directory entry (e.g., assets/images/) not individual file names — so that adding sprites does not require pubspec.yaml edits.

Audio assets

Recommended free sources: freesound.org (CC0 filter), opengameart.org audio section, itch.io free audio packs.

Audio files go in assets/audio/. Add assets/audio/ as a top-level assets entry in pubspec.yaml.

Package: flame_audio (wraps audioplayers). BGM uses FlameAudio.bgm.play(); frequent SFX use an AudioPool (see the Audio patterns in docs/game-gotchas.md).

Audio plan requirements (per docs/game-gotchas.md):

• iOS format: bundle WAV (22 kHz mono 16-bit). iOS does not reliably play OGG — convert OGG/MP3 with ffmpeg -i in.ogg -ac 1 -ar 22050 -sample_fmt s16 out.wav.
• Volume caps: specify safe per-channel caps (e.g. BGM ≤ 0.2, SFX ≤ 0.7) that become the GameConfig defaults; the user slider is a fraction of the cap.

flutter_launcher_icons

Branding art source: by default the generator draws the icon/splash from a shared code painter (tool/gen_icon.dart, design-token colors); choose AI-generated art here instead if the concept warrants it. Either way the generator (§5c.9) runs flutter_launcher_icons / flutter_native_splash and sets the localized app display name — design only specifies intent.

Specify the icon intent so the generator can configure flutter_launcher_icons:

# pubspec.yaml excerpt (dev_dependencies)
flutter_launcher_icons:
  android: true
  ios: true
  remove_alpha_ios: true
  image_path: "assets/icons/icon.png"                    # 1024×1024, no alpha (iOS + legacy)
  adaptive_icon_background: "<hex colour>"               # solid, opaque
  adaptive_icon_foreground: "assets/icons/icon-fg.png"   # safe-zone padded (NOT full-bleed)
  adaptive_icon_monochrome: "assets/icons/icon-mono.png" # Android 13+ themed icon
  min_sdk_android: 21
  web:
    generate: false

The icon must:

• Be 1024×1024 pixels, PNG format; iOS icon.png is opaque (no alpha).
• Follow the app's art direction (character portrait or logo on the Primary background).
• Android adaptive foreground (icon-fg.png): the motif must sit inside the safe zone — the 108dp canvas is masked to ≤72dp and only the centre ~66dp is guaranteed unclipped, so keep ~25% padding on every side. Reusing the full-bleed icon.png here makes the icon look cropped/"zoomed" on Android. Background is a solid colour (Primary/Background), not an image.
• Android themed icon (icon-mono.png): a single-colour (white-on-transparent) silhouette in the same safe zone; Android 13+ tints it to the user's theme. Without it the icon looks out of place among themed icons (Google Play increasingly expects one).

flutter_native_splash

Specify the splash screen intent for flutter_native_splash:

# pubspec.yaml excerpt
flutter_native_splash:
  color: "<Background hex>"          # matches DesignTokens.background
  image: assets/images/splash.png    # centred logo/character, 288×288 px recommended
  android_12:
    color: "<Background hex>"
    image: assets/images/splash.png
    icon_background_color: "<Primary hex>"
  ios: true
  android: true
  web: false

The splash image must:

• Be 288×288 pixels, PNG with transparent background.
• Show the app logo or the main character on a transparent field.
• Feel consistent with the main menu's visual style.

Output

1. Write the design document

Create docs/harness/plans/<YYYY-MM-DD>-design.md (use today's UTC date).

If docs/harness/plans/ does not exist, create it before writing.

The document must include all of the following sections (downstream validators grep for these headings):

• ## Design tokens — with palette table, typography scale, spacing scale
• ## Visual concept — with art direction, sprite list, overlay/HUD layout
• ## Asset/audio plan — with sprite sourcing table, audio table, flutter_launcher_icons config, flutter_native_splash config

Fill every section from the PRD and config.md; do not leave placeholder text.

2. Update state.md

Update docs/harness/state.md per docs/harness-protocol.md §2 and the transition rule in §7 (design → contract). Per §7 rule 2, a skill that completes successfully and advances the pipeline sets status: running together with current_phase and next_role in the same atomic write:

status: running
current_phase: design
next_role: contract
updated_at: "<ISO-8601 UTC now>"

Leave all other keys unchanged. Use Edit for a targeted update.

3. Append to pipeline-log.md

Append one row to docs/harness/pipeline-log.md per docs/harness-protocol.md §6:

| <ISO-8601 UTC now> | complete | design | design_tokens spec written; next: contract |

Error handling

• If the PRD is missing or empty, abort with a clear message and set state.md to status: paused, pause_reason: manual_action.
• If config.md cannot be read, abort immediately (do not write partial output).
• If the genre or tone cannot be determined from the PRD, choose a neutral palette (dark background #1A1A2E, bright accent #E94560) and note the assumption in the design document under a ## Assumptions heading.