修复了一点bug，然后增加了图层拆分更多的功能

lib/client/seedream-layer-compose.ts

@@ -2,6 +2,7 @@ export type SeedreamLayerCompositionItem = {
   url: string;
   visible: boolean;
   box: [number, number, number, number];
+  rotation?: number;
 };
 
 export async function downloadSeedreamLayerComposition(options: {
@@ -14,7 +15,9 @@ export async function downloadSeedreamLayerComposition(options: {
 
   const decoded: Array<{ item: SeedreamLayerCompositionItem; bitmap: ImageBitmap }> = [];
   try {
-    for (const item of options.items) decoded.push({ item, bitmap: await fetchBitmap(item.url) });
+    for (const item of options.items) {
+      if (item.visible) decoded.push({ item, bitmap: await fetchBitmap(item.url) });
+    }
     const reference = decoded[0].bitmap;
     const width = positiveDimension(options.width) || reference.width;
     const height = positiveDimension(options.height) || reference.height;
@@ -26,15 +29,21 @@ export async function downloadSeedreamLayerComposition(options: {
     context.clearRect(0, 0, width, height);
 
     for (const { item, bitmap } of decoded) {
-      if (!item.visible) continue;
       const [left, top, right, bottom] = item.box;
-      context.drawImage(
-        bitmap,
-        left / 1000 * width,
-        top / 1000 * height,
-        Math.max(1, (right - left) / 1000 * width),
-        Math.max(1, (bottom - top) / 1000 * height)
-      );
+      const x = left / 1000 * width;
+      const y = top / 1000 * height;
+      const itemWidth = Math.max(1, (right - left) / 1000 * width);
+      const itemHeight = Math.max(1, (bottom - top) / 1000 * height);
+      const rotation = Number.isFinite(item.rotation) ? item.rotation || 0 : 0;
+      if (!rotation) {
+        context.drawImage(bitmap, x, y, itemWidth, itemHeight);
+        continue;
+      }
+      context.save();
+      context.translate(x + itemWidth / 2, y + itemHeight / 2);
+      context.rotate(rotation * Math.PI / 180);
+      context.drawImage(bitmap, -itemWidth / 2, -itemHeight / 2, itemWidth, itemHeight);
+      context.restore();
     }
 
     const blob = await canvasBlob(canvas, "image/png");