// 定義水印函數(shù)
const addWatermark = ({
  container = document.body, // 水印添加到的容器，默認(rèn)為 body
  width = "200px", // 水印 canvas 的寬度
  height = "100px", // 水印 canvas 的高度
  textAlign = "center", // 水印文字的對(duì)齊方式
  textBaseline = "middle", // 水印文字的基線
  font = "16px Microsoft Yahei", // 水印文字的字體
  fillStyle = "rgba(184, 184, 184, 0.6)", // 水印文字的填充樣式
  content = "我是水印", // 水印文字的內(nèi)容
  rotate = -30, // 水印文字的旋轉(zhuǎn)角度
  zIndex = 10000, // 水印的 z-index 值
}) => {
  // 生成水印 canvas
  const canvas = document.createElement("canvas");
  canvas.setAttribute("width", width);
  canvas.setAttribute("height", height);
  const ctx = canvas.getContext("2d");
  ctx.textAlign = textAlign;
  ctx.textBaseline = textBaseline;
  ctx.font = font;
  ctx.fillStyle = fillStyle;
  ctx.rotate((Math.PI / 180) * rotate);
  ctx.fillText(content, parseFloat(width) / 2, parseFloat(height) / 1);
  // 將 canvas 轉(zhuǎn)換為 base64 URL
  const base64Url = canvas.toDataURL("image/png");
  console.log(base64Url);
  const __wm = document.querySelector(".__wm");
  const watermarkDiv = __wm || document.createElement("div");
  const styleStr = `
              position: fixed;
              top: 0;
              left: 0;
              bottom: 0;
              right: 0;
              width: 100%;
              height: 100%;
              z-index: ${zIndex};
              pointer-events: none;
              background: url('${base64Url}') left top repeat;
          `;
  watermarkDiv.setAttribute("style", styleStr);
  watermarkDiv.classList.add("__wm");
  // 則創(chuàng)建一個(gè) div 并設(shè)置樣式和類名
  if (!__wm) {
    container.style.position = "relative";
    container.insertBefore(watermarkDiv, container.firstChild);
  }
  // 監(jiān)聽容器變化，當(dāng)容器發(fā)生變化時(shí)重新調(diào)用 addWatermark 函數(shù)
  const { MutationObserver } = window;
  if (MutationObserver) {
    let mo = new MutationObserver(function () {
      const __wm = document.querySelector(".__wm");
      // 只在__wm元素變動(dòng)才重新調(diào)用__canvasWM
      if ((__wm && __wm.getAttribute("style") !== styleStr) || !__wm) {
        // 避免一直觸發(fā)
        mo.disconnect();
        mo = new MutationObserver(() => {});
        addWatermark({
          container: document.getElementById("app"),
          width: "200px",
          height: "100px",
          textAlign: "center",
          textBaseline: "middle",
          font: "16px Microsoft Yahei",
          fillStyle: "rgba(184, 184, 184, 0.3 )",
          content,
          rotate: -30,
          zIndex: 10000,
        });
      }
    });
    mo.observe(container, {
      attributes: true,
      subtree: true,
      childList: true,
    });
  }
};
export default addWatermark;

import addWatermark from "@/utils/shuiyin";
Vue.use(addWatermark);