feat(write-sprite): compose atlas image + UV-JSON + lock output

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 };