[feat] add background param

.gitignore

@@ -6,3 +6,5 @@ temp
 yarn.lock
 __diff_output__
 .jest*
+
+.idea

src/canvasFactory.ts

@@ -15,7 +15,11 @@ export class NodeCanvasFactory {
   create(width: number, height: number): NonNullableFactory {
     invariant(width > 0 && height > 0, "Invalid canvas size");
     const canvas = Canvas.createCanvas(width, height);
-    const context = canvas.getContext("2d");
+    const context = canvas.getContext("2d", { alpha: true });
+
+    // 确保 canvas 背景是透明的
+    context.clearRect(0, 0, width, height);
+
     return {
       canvas,
       context,

src/index.ts

@@ -5,6 +5,7 @@ import * as pdfjs from "pdfjs-dist/legacy/build/pdf.mjs";
 import type { DocumentInitParameters } from "pdfjs-dist/types/src/display/api.js";
 import { NodeCanvasFactory } from "./canvasFactory.js";
 import { parseInput } from "./parseInput.js";
+import { CanvasGradient, CanvasPattern } from "canvas";
 
 const pdfjsPath = path.dirname(
   createRequire(import.meta.url).resolve("pdfjs-dist/package.json")
@@ -39,6 +40,7 @@ export type Options = {
   password?: string;
   /** defaults to `1`. If you want high-resolution images, increase this */
   scale?: number;
+  background?: string | CanvasGradient | CanvasPattern | undefined;
   /** document init parameters which are passed to pdfjs.getDocument */
   docInitParams?: Partial<DocumentInitParameters>;
 };
@@ -101,13 +103,13 @@ export async function pdf(
       viewport.width,
       viewport.height
     );
-
     await page.render({
       canvasContext: context,
       viewport,
+      background: options.background,
     }).promise;
 
-    return canvas.toBuffer();
+    return canvas.toBuffer("image/png");
   }
 
   return {