核心代码

import EXIF from "exif-js";

// 入口
const waterMarkToPanel = async (panelFile, waterMarkFile) => {
  const orientation = await getOrientation(panelFile);

  const panelBase64Url = await getBase64(panelFile);

  const waterMarkBase64Url = await getBase64(waterMarkFile);

  // 获取panel图片的原生宽度、高度、图片元素
  const panelNatureData = await getNatureData(panelBase64Url);

  // 获取水印图片的原生宽度、高度、图片元素
  const waterMarkNatureData = await getNatureData(waterMarkBase64Url);

  // 处理画布旋转/加水印
  return startDraw(orientation, panelNatureData, waterMarkNatureData);
};


// 开始处理画布并加水印
const startDraw = (orientation, panelNatureData, waterMarkNatureData) => {

  const canvas = document.createElement("canvas");

  const ctx: any = canvas.getContext("2d");

  // panel图片数据
  const { naturalWidth, naturalHeight, element: panelEle} =  panelNatureData;

  // waterMark图片数据
  const { naturalWidth: wNatureWidth, naturalHeight: wNatureHeight, element: waterMarkEle} =  waterMarkNatureData;

  // 处理画布旋转, 移动端存在一些兼容性，ios之类
  switch (Number(orientation)) {
    case 6:
      console.log("照片顺时针旋转了270度");
      canvas.width = naturalHeight; // 注意这里，canvas宽度实际取的是图片高度，因为图片的方位是旋转过270度的，以下类试
      canvas.height = naturalWidth;

      ctx.rotate((90 * Math.PI) / 180); // 既然照片方位顺时针转了270度，那再转90度，相当于一共转了360度，相当于没转，这是方位就正确了
      ctx.translate(0, -canvas.width); // 转了90度，是不是位置也变了，想想图片在第一象限，绕原点顺时针转了90度，那就转到第二象限了，那就需要超y方向移上去
      ctx.drawImage(panelEle, 0, 0, canvas.height, canvas.width); // 画图
      // 恢复坐标 画完图，需要将canvas恢复原位，不解释了，有点绕
      ctx.translate(0, canvas.width);
      ctx.rotate((-90 * Math.PI) / 180);
      break;
    case 8:
      console.log("照片顺时针旋转90度");
      canvas.width = naturalHeight;
      canvas.height = naturalWidth;
      ctx.rotate((-90 * Math.PI) / 180);
      ctx.translate(-canvas.height, 0);
      ctx.drawImage(panelEle, 0, 0, canvas.height, canvas.width);

      // 恢复坐标
      ctx.translate(canvas.height, 0);
      ctx.rotate((90 * Math.PI) / 180);
      break;
    case 3:
      console.log("照片顺时针旋转180度");
      canvas.width = naturalWidth;
      canvas.height = naturalHeight;
      ctx.rotate((180 * Math.PI) / 180);
      ctx.translate(-canvas.width, -canvas.height);
      ctx.drawImage(panelEle, 0, 0, canvas.width, canvas.height);

      // 恢复坐标
      ctx.translate(canvas.width, canvas.height);
      ctx.rotate((-180 * Math.PI) / 180);
      break;
    default:
      canvas.width = naturalWidth;
      canvas.height = naturalHeight;
      ctx.drawImage(panelEle, 0, 0, canvas.width, canvas.height);
      break;
  }

  // 在画布上加水印 canvas.drawImage https://www.runoob.com/try/try.php?filename=tryhtml5_canvas_drawimage
  ctx.drawImage(
    waterMarkEle,
    (40 / 750) * canvas.width,
    canvas.height - ((40+ wNatureHeight) / 750) * canvas.width,
    (wNatureWidth / 750) * canvas.width,
    (wNatureHeight / 750) * canvas.width
  );

  const url = canvas.toDataURL("image/jpeg"); // 最终图片url
  const file = dataURItoBlob(url); // 最终图片file

  return {
    url,
    file
  }
};

工具函数

// 获取照片方向
const getOrientation = (file) => {
  return new Promise((resolve, reject) => {
    const currentVersion = getVersion(); // ios 版本号
    const support = testVersion(currentVersion, "13.4.1"); // ios版本号大于13.4.1， 无需特殊处理

    if (browserInfo.versions.ios && support) {
      resolve(1);
    } else {
      EXIF.getData(file, () => {
        resolve(EXIF.getTag(file, "Orientation"));
      });
    }
  });
};

// 获取base64
const getBase64 = (file) => {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.addEventListener("load", () => resolve(reader.result));
    reader.readAsDataURL(file);
  });
};

// 获取图片原生尺寸
const getNatureData = (imgUrl) => {
  return new Promise((resolve, reject) => {
    const img = new Image();
    img.setAttribute("crossOrigin", "Anonymous");
    img.onload = (e: any) => {
      resolve({
        element: img
        naturalWidth: e.target.naturalWidth,
        naturalHeight: e.target.naturalHeight,
      });
    };
    img.src = imgUrl;
  });
};

// 判断ios版本 preVersion是否大于lastVersion
export const testVersion = (
  preVersion: string = "",
  lastVersion: string = ""
) => {
  const sources = preVersion.split(".");
  const dests = lastVersion.split(".");
  const maxL = Math.max(sources.length, dests.length);
  let result = true;
  for (let i = 0; i < maxL; i++) {
    let preValue = sources.length > i ? sources[i] : "0";
    let preNum = isNaN(Number(preValue))
      ? preValue.charCodeAt(0)
      : Number(preValue);
    let lastValue = dests.length > i ? dests[i] : "0";
    let lastNum = isNaN(Number(lastValue))
      ? lastValue.charCodeAt(0)
      : Number(lastValue);
    if (preNum < lastNum) {
      result = false;
      break;
    } else if (preNum > lastNum) {
      result = true;
      break;
    }
  }
  return result;
};

export const getVersion = () => {
  const str = navigator.userAgent.toLowerCase();
  const version = str.match(/cpu iphone os (.*?) like mac os/);
  let currentVersion = "0.0.0"; // ios 版本号
  if (version && version[1]) {
    currentVersion = version[1].replace(/_/g, ".");
  }
  return currentVersion;
};

// 转换为 blob 直接传输 暂时无用
export const dataURItoBlob = (dataURI: string) => {
  // convert base64 to raw binary data held in a string
  // doesn't handle URLEncoded DataURIs
  var byteString = atob(dataURI.split(",")[1]);

  // separate out the mime component
  var mimeString = dataURI
    .split(",")[0]
    .split(":")[1]
    .split(";")[0];

  // write the bytes of the string to an ArrayBuffer
  var ab = new ArrayBuffer(byteString.length);
  var ia = new Uint8Array(ab);
  for (var i = 0; i < byteString.length; i++) {
    ia[i] = byteString.charCodeAt(i);
  }

  try {
    // 新版本浏览器
    return new window.Blob([ia], { type: mimeString });
  } catch (e) {
    // TypeError old chrome and FF
    // Android 中该方式无效
    window.BlobBuilder =
      window.BlobBuilder ||
      window.WebKitBlobBuilder ||
      window.MozBlobBuilder ||
      window.MSBlobBuilder;

    if (e.name === "TypeError" && window.BlobBuilder) {
      var bb = new window.BlobBuilder();
      bb.append(ab);
      return bb.getBlob(mimeString);
    } else {
      return null;
    }
  }
};

demo尝试

https://codesandbox.io/s/canv...