From d5fb03b8d0b48fe1584b0d5a3adddae6dc8c9348 Mon Sep 17 00:00:00 2001
From: Axel Meyer <axel.meyer@durania.net>
Date: Tue, 16 Jun 2026 21:17:32 +0200
Subject: [PATCH] feat(write-sprite): compose atlas image + UV-JSON + lock
 output

---
 src/write-sprite.js        | 58 ++++++++++++++++++++++++++++++++++++++
 tests/write-sprite.test.js | 46 ++++++++++++++++++++++++++++++
 2 files changed, 104 insertions(+)
 create mode 100644 src/write-sprite.js
 create mode 100644 tests/write-sprite.test.js

diff --git a/src/write-sprite.js b/src/write-sprite.js
new file mode 100644
index 0000000..7d4e212
--- /dev/null
+++ b/src/write-sprite.js
@@ -0,0 +1,58 @@
+// src/write-sprite.js
+// Compose the diffuse atlas image, build the UV-JSON, write all three
+// output files into <outDir>/<atlasId>/.
+
+const fs = require('node:fs');
+const path = require('node:path');
+const Jimp = require('jimp');
+const { serializeSpriteLock } = require('./lock-sprite');
+
+async function composeSpriteAtlas(boundsW, boundsH, placed) {
+    // Jimp 0.22: synchronous (w, h, color) constructor; color is RGBA32.
+    const atlas = new Jimp(boundsW, boundsH, 0x00000000);
+    for (const p of placed) {
+        // Each `p` carries the source image as `p.image` (jimp instance).
+        // Blit at (p.x, p.y) — the orchestrator has already pre-offset
+        // these coordinates by padPx, so x/y is the INNER sprite origin.
+        atlas.composite(p.image, p.x, p.y);
+    }
+    return atlas;
+}
+
+function buildUvJson(atlasId, boundsW, boundsH, placed) {
+    const sprites = {};
+    for (const p of placed) {
+        sprites[p.alias] = {
+            x: p.x,
+            y: p.y,
+            w: p.w,
+            h: p.h,
+            source_file: p.sourceFile,
+        };
+    }
+    return JSON.stringify({
+        atlas_id: atlasId,
+        atlas_size: [boundsW, boundsH],
+        sprites,
+    }, null, 2) + '\n';
+}
+
+async function writeSpriteOutputs(opts) {
+    const { atlasId, outDir, placed, boundsW, boundsH, lock } = opts;
+    const atlasDir = path.join(outDir, atlasId);
+    fs.mkdirSync(atlasDir, { recursive: true });
+
+    const atlas = await composeSpriteAtlas(boundsW, boundsH, placed);
+    await atlas.writeAsync(path.join(atlasDir, 'sprites.diffuse.atlas.png'));
+
+    fs.writeFileSync(
+        path.join(atlasDir, 'sprites.uv.json'),
+        buildUvJson(atlasId, boundsW, boundsH, placed),
+    );
+    fs.writeFileSync(
+        path.join(atlasDir, 'sprites.atlas.lock.json'),
+        serializeSpriteLock(lock),
+    );
+}
+
+module.exports = { composeSpriteAtlas, buildUvJson, writeSpriteOutputs };
diff --git a/tests/write-sprite.test.js b/tests/write-sprite.test.js
new file mode 100644
index 0000000..bb16106
--- /dev/null
+++ b/tests/write-sprite.test.js
@@ -0,0 +1,46 @@
+const { test } = require('node:test');
+const assert = require('node:assert');
+const fs = require('node:fs');
+const path = require('node:path');
+const os = require('node:os');
+const Jimp = require('jimp');
+const { writeSpriteOutputs, buildUvJson } = require('../src/write-sprite');
+
+test('buildUvJson: emits atlas_id + atlas_size + sprites table', () => {
+    const placed = [
+        { alias: 'bed1', x: 0,  y: 0, w: 64, h: 32, sourceFile: 'Bed1.png' },
+        { alias: 'sack', x: 64, y: 0, w: 32, h: 32, sourceFile: 'Sack.png' },
+    ];
+    const json = buildUvJson('tcbasics', 96, 32, placed);
+    const parsed = JSON.parse(json);
+    assert.strictEqual(parsed.atlas_id, 'tcbasics');
+    assert.deepStrictEqual(parsed.atlas_size, [96, 32]);
+    assert.strictEqual(parsed.sprites.bed1.x, 0);
+    assert.strictEqual(parsed.sprites.bed1.w, 64);
+    assert.strictEqual(parsed.sprites.bed1.source_file, 'Bed1.png');
+    assert.strictEqual(parsed.sprites.sack.x, 64);
+});
+
+test('writeSpriteOutputs: produces 3 files', async (t) => {
+    const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'write-sprite-test-'));
+    t.after(() => fs.rmSync(tmp, { recursive: true, force: true }));
+
+    // Build a 2-sprite atlas in memory
+    const a = new Jimp(32, 32, 0xff0000ff);
+    const b = new Jimp(32, 32, 0x00ff00ff);
+    const placed = [
+        { alias: 'red',   x: 0,  y: 0, w: 32, h: 32, sourceFile: 'Red.png',   image: a, padPx: 0 },
+        { alias: 'green', x: 32, y: 0, w: 32, h: 32, sourceFile: 'Green.png', image: b, padPx: 0 },
+    ];
+    await writeSpriteOutputs({
+        atlasId: 'test',
+        outDir: tmp,
+        placed,
+        boundsW: 64,
+        boundsH: 32,
+        lock: { atlas_id: 'test', version: 1, aliases: ['red', 'green'], sources: { red: 'Red.png', green: 'Green.png' } },
+    });
+    assert.ok(fs.existsSync(path.join(tmp, 'test/sprites.diffuse.atlas.png')));
+    assert.ok(fs.existsSync(path.join(tmp, 'test/sprites.uv.json')));
+    assert.ok(fs.existsSync(path.join(tmp, 'test/sprites.atlas.lock.json')));
+});