fabricjs 滤镜 Worker

FabricImage.applyFilters() 是同步的。它要把每个滤镜作用到每个像素之后，页面才能重绘或响应点击，所以对大照片做图片模糊会让编辑器卡住（fabric.js #9532）。Fabric 的 WebGL 后端对部分滤镜更快，但工作仍然在主线程上进行，GPU 较慢或 WebGL 上下文丢失时还会退回 2D 方式。createFilterWorker 会把 fabricjs 滤镜放到 Web Worker 中运行。

试一试

对一张 2400 × 1500 的图片做模糊、锐化和饱和度。注意转圈的图标。

正在加载在线示例，代码在下方。

filter-worker-demo.tsx

"use client";
 
import { FabricImage, filters } from "fabric";
import {
  createFilterWorker,
  type FilterWorker,
  type ImageFilter,
} from "fabricjs-document-engine/filters";
import { CpuIcon, RotateCcwIcon, SnailIcon } from "lucide-react";
import { useTranslations } from "next-intl";
import { useEffect, useRef, useState } from "react";
 
import { DemoCanvas, DemoFrame, Status, Toolbar, ToolButton } from "./demo-ui";
import { PAGE, useFabricCanvas } from "./use-fabric-canvas";
 
const SOURCE = { width: 2400, height: 1500 };
 
function photo() {
  const element = document.createElement("canvas");
  element.width = SOURCE.width;
  element.height = SOURCE.height;
  const ctx = element.getContext("2d")!;
  const sky = ctx.createLinearGradient(0, 0, 0, SOURCE.height);
  sky.addColorStop(0, "#7ad9ec");
  sky.addColorStop(0.6, "#ffd666");
  sky.addColorStop(1, "#f2836f");
  ctx.fillStyle = sky;
  ctx.fillRect(0, 0, SOURCE.width, SOURCE.height);
  for (let index = 0; index < 600; index += 1) {
    ctx.fillStyle = `hsl(${(index * 47) % 360} 70% ${40 + (index % 30)}%)`;
    ctx.beginPath();
    ctx.arc(
      (index * 389) % SOURCE.width,
      (index * 251) % SOURCE.height,
      10 + (index % 50),
      0,
      Math.PI * 2
    );
    ctx.fill();
  }
  return element.toDataURL("image/jpeg", 0.9);
}
 
const heavy = (): ImageFilter[] => [
  new filters.Blur({ blur: 0.25 }),
  new filters.Convolute({ matrix: [0, -1, 0, -1, 5, -1, 0, -1, 0] }),
  new filters.Saturation({ saturation: 0.4 }),
];
 
function measureFreeze(work: () => Promise<unknown>) {
  const channel = new MessageChannel();
  let last = performance.now();
  let longest = 0;
  let running = true;
  channel.port1.onmessage = () => {
    const now = performance.now();
    longest = Math.max(longest, now - last);
    last = now;
    if (running) channel.port2.postMessage(null);
  };
  channel.port2.postMessage(null);
  return work().then(() => {
    running = false;
    channel.port1.close();
    return Math.round(Math.max(longest, performance.now() - last));
  });
}
 
export default function FilterWorkerDemo() {
  const t = useTranslations("demos");
  const { elementRef, canvas } = useFabricCanvas();
  const imageRef = useRef<FabricImage | null>(null);
  const workerRef = useRef<FilterWorker | null>(null);
  const spinnerRef = useRef<HTMLSpanElement>(null);
  const [busy, setBusy] = useState(false);
  const [progress, setProgress] = useState(0);
  const [message, setMessage] = useState("");
 
  useEffect(() => {
    if (!canvas) return;
    let cancelled = false;
    const worker = createFilterWorker();
    workerRef.current = worker;
    void FabricImage.fromURL(photo()).then((image) => {
      if (cancelled) return;
      image.scaleToWidth(PAGE.width);
      image.set({
        left: 0,
        top: 0,
        originX: "left",
        originY: "top",
        selectable: false,
      });
      imageRef.current = image;
      canvas.add(image);
      canvas.requestRenderAll();
    });
    let frame = 0;
    let angle = 0;
    const spin = () => {
      angle = (angle + 6) % 360;
      if (spinnerRef.current)
        spinnerRef.current.style.transform = `rotate(${angle}deg)`;
      frame = requestAnimationFrame(spin);
    };
    frame = requestAnimationFrame(spin);
    return () => {
      cancelled = true;
      cancelAnimationFrame(frame);
      worker.terminate();
      if (imageRef.current) canvas.remove(imageRef.current);
      imageRef.current = null;
    };
  }, [canvas]);
 
  async function run(inWorker: boolean) {
    const image = imageRef.current;
    const worker = workerRef.current;
    if (!canvas || !image || !worker || busy) return;
    setBusy(true);
    setProgress(0);
    setMessage(t("filters.running"));
    await new Promise((resolve) => setTimeout(resolve, 50));
    const freeze = await measureFreeze(async () => {
      if (inWorker) {
        await worker.apply(image, heavy(), { onProgress: setProgress });
      } else {
        image.filters = heavy() as never;
        image.applyFilters();
        setProgress(1);
      }
      canvas.requestRenderAll();
    });
    setMessage(
      inWorker
        ? t("filters.workerResult", { freeze, mode: worker.mode })
        : t("filters.fabricResult", { freeze })
    );
    setBusy(false);
  }
 
  async function reset() {
    const image = imageRef.current;
    if (!canvas || !image || !workerRef.current) return;
    await workerRef.current.apply(image, []);
    setProgress(0);
    setMessage("");
  }
 
  return (
    <DemoFrame>
      <DemoCanvas elementRef={elementRef} label={t("canvas")}>
        <span
          ref={spinnerRef}
          aria-hidden
          className="absolute top-2 right-2 size-5 rounded-full border-2 border-[#6f00ff] border-t-transparent"
        />
      </DemoCanvas>
 
      <div className="h-1.5 w-full overflow-hidden rounded-full bg-muted">
        <div
          className="h-full bg-[#6f00ff] transition-[width]"
          style={{ width: `${Math.round(progress * 100)}%` }}
        />
      </div>
 
      <Toolbar>
        <ToolButton
          icon={CpuIcon}
          label={t("filters.worker")}
          primary
          disabled={!canvas || busy}
          onClick={() => void run(true)}
        />
        <ToolButton
          icon={SnailIcon}
          label={t("filters.fabric")}
          disabled={!canvas || busy}
          onClick={() => void run(false)}
        />
        <ToolButton
          icon={RotateCcwIcon}
          label={t("filters.reset")}
          iconOnly
          disabled={!canvas || busy}
          onClick={() => void reset()}
        />
      </Toolbar>
 
      <Status tone={busy ? "busy" : message ? "ok" : "idle"}>
        {message || t("filters.hint")}
      </Status>
    </DemoFrame>
  );
}

分别在 Worker 中和用 Fabric 运行同样的模糊，注意角落里的旋转图标。页面卡住时它就会停下。状态栏会显示最长一次卡顿的毫秒数。

在 Worker 中运行滤镜

import { filters } from "fabric";
import { createFilterWorker } from "fabricjs-document-engine/filters";
 
const filterWorker = createFilterWorker({ engine });
 
await filterWorker.apply(image, [
  new filters.Blur({ blur: 0.2 }),
  new filters.Brightness({ brightness: 0.1 }),
]);

图片以 ImageBitmap 的形式传给 Worker，结果也以同样的方式传回。两者都是转移，而不是复制。
Worker 在 OffscreenCanvas 上绘制，并使用 Fabric 自己的滤镜类，所以结果和 Fabric 的 2D canvas滤镜像素相同。
结果准备好之后图片才会改变。传入 engine 时，这次修改算一步撤销，并随文档保存。
图片更新后，apply 返回 true。

进度和最新一次优先

只改变单个像素的滤镜，例如亮度、对比度和颜色矩阵，会按行分块一起运行，每块完成后报告一次进度。模糊、卷积和像素化则作为一步作用于整张图片。

slider.addEventListener("input", () => {
  void filterWorker.apply(
    image,
    [new filters.Blur({ blur: Number(slider.value) })],
    {
      onProgress: (done) => (progress.value = done),
    }
  );
});

拖动滑块时，同一张图片的每次新运行都会取消上一次，旧的 promise 返回 false。只有最后一个值会被绘制。

取消

const controller = new AbortController();
const run = filterWorker.apply(image, heavyFilters, {
  signal: controller.signal,
});
controller.abort();
await run.catch(() => undefined);

被取消的运行会以 signal 的 reason 拒绝，图片保持原样。

在哪里运行

情况	滤镜在哪里运行
支持模块 Worker 和 `OffscreenCanvas`（Chrome 80、Firefox 114、Safari 16.4 及以上）	在 web worker 中
较旧的浏览器，或 CommonJS 构建	在主线程上分成小步运行，每步之后暂停一下
BlendImage、Resize 或你自己的滤镜类	使用 Fabric 的 `applyFilters`

filterWorker.mode 会告诉你使用的是哪一种。Vite、webpack 和 Next.js 会自动处理 Worker 文件。如果想有意在主线程上运行，例如在测试中，请传入 worker: false；在其他环境中，可以用 createWorker 自己创建 Worker。

const filterWorker = createFilterWorker({ worker: false });

所有配置项都在滤镜 API里。对象太多导致绘制变慢，请看渲染大量对象。fabricjs 滤镜保留在 filters 数组中，保存的文档重新打开后效果不变。

图片滤镜

试一试

在 Worker 中运行滤镜

进度和最新一次优先

取消

在哪里运行