make-sheet.mjs

#!/usr/bin/env node
import sharp from 'sharp';
import { parseArgs } from 'node:util';

const { values, positionals } = parseArgs({
    options: {
        out: { type: 'string' },
    },
    allowPositionals: true,
});

if (!values.out || positionals.length === 0) {
    console.error('Usage: node scripts/make-sheet.mjs --out sheet.png frame1.png frame2.png ...');
    process.exit(1);
}

const frames = positionals;
const firstMeta = await sharp(frames[0]).metadata();
const w = firstMeta.width;
const h = firstMeta.height;

const composites = [];
for (let i = 0; i < frames.length; i++) {
    composites.push({
        input: await sharp(frames[i]).resize(w, h).toBuffer(),
                    left: i * w,
                    top: 0,
    });
}

await sharp({
    create: {
        width: w * frames.length,
        height: h,
        channels: 4,
        background: { r: 0, g: 0, b: 0, alpha: 0 },
    },
})
.composite(composites)
.png()
.toFile(values.out);

console.log(`Saved: ${values.out} (${frames.length} frames, ${w}x${h} each)`);