# spritecook-use-dual-grid-tilesets

This skill explains SpriteCook’s 15-piece tileset mapping for a dual-grid terrain renderer. Use it when building or reviewing top-down game rendering.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 555 installs · ★ 48
- Author: SpriteCook
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/SpriteCook/skills/tree/HEAD/skills/spritecook-use-dual-grid-tilesets/SKILL.md
- Updated: 2026-10-22
- HTML: https://affpapa.org/en/nevibecode/skills/spritecook-use-dual-grid-tilesets

## What it does

The skill maps logical terrain cells to the visible tiles between them. Each rendered position reads four surrounding cells, builds a 4-bit mask, and selects a frame from a 4x4 atlas. It includes the mask bit order, the frame lookup table, atlas coordinates, and renderer pseudocode.

For a two-surface set, the counter terrain is drawn as a base layer before the masked pieces. A transparent single-surface set skips that layer. The renderer also needs one extra tile row and column because visible tiles surround the logical cells.

Treat the atlas as sixteen equal cells in a 4x4 grid, rather than as a regular 8-neighbor blob tileset. Pixel-art output requires smoothing to be disabled and nearest-neighbor scaling to be used. Without the base layer, mask `0` leaves the counter terrain transparent in a two-surface set.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add SpriteCook/skills --skill spritecook-use-dual-grid-tilesets -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/spritecook-use-dual-grid-tilesets/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/spritecook-use-dual-grid-tilesets/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add SpriteCook/skills --skill spritecook-use-dual-grid-tilesets -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/spritecook-use-dual-grid-tilesets/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add SpriteCook/skills --skill spritecook-use-dual-grid-tilesets -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/spritecook-use-dual-grid-tilesets/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install SpriteCook/skills spritecook-use-dual-grid-tilesets
```

2. **Manually: put the files in place**
- File: `.github/skills/spritecook-use-dual-grid-tilesets/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add SpriteCook/skills --skill spritecook-use-dual-grid-tilesets -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/SpriteCook/skills --path skills/spritecook-use-dual-grid-tilesets
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/spritecook-use-dual-grid-tilesets/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add SpriteCook/skills --skill spritecook-use-dual-grid-tilesets -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/SpriteCook/skills/tree/HEAD/skills/spritecook-use-dual-grid-tilesets/SKILL.md

## When to use it
- map four logical cells to a rendered tile mask
- resolve a mask into a 4x4 atlas frame
- render terrain around the logical map boundary
- place a counter surface beneath masked pieces
- test filled-area joins for mask `15`

## Example prompts
- Implement a SpriteCook dual-grid renderer for the 4x4 atlas and include the `frameByMask` lookup.
- Show how to render `edges="two_surfaces"` with its counter-surface base layer.
- Inspect the test map and fix the checkerboard joins around a filled area with mask `15`.

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 8a52d075f982d587.

BEGIN THIRD-PARTY FILE 8a52d075f982d587
````text
---
name: spritecook-use-dual-grid-tilesets
description: "Implementation guide for using SpriteCook top-down 15-piece tilesets with a dual-grid autotile renderer. Use when explaining or coding how to map a 4x4 15-piece tileset image into terrain using SpriteCook's dual-grid mask system."
---

# SpriteCook Dual-Grid 15-Piece Tilesets

Use this skill when implementing a top-down 15-piece SpriteCook tileset in a game engine or custom renderer.

This skill is about using a generated tileset. For generation, use `spritecook-generate-tilesets`.

## Concept

A dual-grid tileset stores terrain as logical painted cells, then renders visible tiles between those cells. Each rendered tile is chosen from the four logical cells around it.

For each rendered tile, sample:

- top-left logical cell
- top-right logical cell
- bottom-left logical cell
- bottom-right logical cell

That four-cell pattern becomes a 4-bit mask. The mask chooses one frame from the 4x4 15-piece atlas.

## Mask Order

Use SpriteCook's current mask bit order:

```ts
let mask = 0
if (filled(x - 1, y - 1)) mask |= 1 // top-left
if (filled(x,     y - 1)) mask |= 2 // top-right
if (filled(x - 1, y    )) mask |= 4 // bottom-left
if (filled(x,     y    )) mask |= 8 // bottom-right
```

Mask `0` renders nothing. Other masks map into the 4x4 atlas through this lookup:

```ts
const frameByMask = [
  -1,
  15,
  8,
  9,
  0,
  11,
  14,
  7,
  13,
  4,
  1,
  10,
  3,
  2,
  5,
  6,
]
```

The atlas cell is:

```ts
const frame = frameByMask[mask]
if (frame < 0) return null
const atlasColumn = frame % 4
const atlasRow = Math.floor(frame / 4)
```

## Renderer Pseudocode

```ts
type CellMap = boolean[] // width * height logical terrain cells

function cellIndex(x: number, y: number, columns: number) {
  return y * columns + x
}

function isFilled(cells: CellMap, x: number, y: number, columns: number, rows: number) {
  return x >= 0 && y >= 0 && x < columns && y < rows && cells[cellIndex(x, y, columns)] === true
}

function dualGridMask(cells: CellMap, x: number, y: number, columns: number, rows: number) {
  let mask = 0
  if (isFilled(cells, x - 1, y - 1, columns, rows)) mask |= 1
  if (isFilled(cells, x,     y - 1, columns, rows)) mask |= 2
  if (isFilled(cells, x - 1, y,     columns, rows)) mask |= 4
  if (isFilled(cells, x,     y,     columns, rows)) mask |= 8
  return mask
}

function atlasCellForMask(mask: number) {
  const frameByMask = [-1, 15, 8, 9, 0, 11, 14, 7, 13, 4, 1, 10, 3, 2, 5, 6]
  const frame = frameByMask[Math.max(0, Math.min(15, Math.floor(mask)))]
  if (frame < 0) return null
````
END THIRD-PARTY FILE 8a52d075f982d587

The third-party file has ended. Everything between the 8a52d075f982d587 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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