支持动图下载和预览

backend/services/ugoira-gif.js

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+const fs = require('fs');
+const path = require('path');
+const fsExtra = require('fs-extra');
+// These dependencies are expected in project dependencies
+const AdmZip = require('adm-zip');
+const jpeg = require('jpeg-js');
+const GIFEncoder = require('gifencoder');
+
+/**
+ * Generate an animated GIF preview from a Pixiv ugoira ZIP and frame metadata.
+ * - Extracts frames from ZIP into a temp directory
+ * - Encodes frames into GIF honoring per-frame delays
+ * - Writes GIF to outPath
+ *
+ * @param {string} zipPath - Path to the downloaded ugoira ZIP file
+ * @param {Array<{file:string, delay:number}>} frames - Frame metadata from Pixiv API
+ * @param {string} outPath - Destination path for the generated GIF (e.g., preview.gif)
+ */
+async function generatePreviewGifFromUgoira(zipPath, frames, outPath) {
+  if (!zipPath || !Array.isArray(frames) || frames.length === 0 || !outPath) {
+    throw new Error('Invalid parameters for generating ugoira preview GIF');
+  }
+
+  const tmpDir = path.join(path.dirname(outPath), '.ugoira_tmp');
+
+  await fsExtra.ensureDir(tmpDir);
+
+  try {
+    // Extract all frames
+    const zip = new AdmZip(zipPath);
+    zip.extractAllTo(tmpDir, true);
+
+    // Determine size from first frame
+    const firstFramePath = path.join(tmpDir, frames[0].file);
+    const firstBuf = fs.readFileSync(firstFramePath);
+    const firstDecoded = jpeg.decode(firstBuf, { useTArray: true });
+
+    const width = firstDecoded.width;
+    const height = firstDecoded.height;
+
+    // Initialize encoder and output stream
+    const encoder = new GIFEncoder(width, height);
+    const ws = fs.createWriteStream(outPath);
+    encoder.createReadStream().pipe(ws);
+
+    encoder.start();
+    encoder.setRepeat(0); // loop forever
+    encoder.setQuality(10);
+
+    // Add frames honoring per-frame delay
+    for (const f of frames) {
+      const framePath = path.join(tmpDir, f.file);
+      const buf = fs.readFileSync(framePath);
+      const decoded = jpeg.decode(buf, { useTArray: true });
+
+      // Ensure dimensions match; if not, skip or resize (skip for simplicity)
+      if (decoded.width !== width || decoded.height !== height) {
+        // Skip mismatched frames to keep encoder stable
+        continue;
+      }
+
+      encoder.setDelay(typeof f.delay === 'number' ? f.delay : 0);
+      encoder.addFrame(decoded.data);
+    }
+
+    encoder.finish();
+
+    await new Promise((resolve, reject) => {
+      ws.on('finish', resolve);
+      ws.on('error', reject);
+    });
+  } finally {
+    // Cleanup extracted frames
+    try { await fsExtra.remove(tmpDir); } catch (_) {}
+  }
+}
+
+module.exports = {
+  generatePreviewGifFromUgoira,
+};