JLH/JLHWEB/src/directives/modules/waterMarker.ts

/*
  需求：给整个页面添加背景水印。

  思路：
    1、使用 canvas 特性生成 base64 格式的图片文件，设置其字体大小，颜色等。
    2、将其设置为背景图片，从而实现页面或组件水印效果
  
  使用：设置水印文案，颜色，字体大小即可
  <div v-waterMarker="{text:'版权所有',textColor:'rgba(180, 180, 180, 0.4)'}"></div>
*/

import type { Directive, DirectiveBinding } from "vue";
const addWaterMarker: Directive = (str: string, parentNode: any, font: any, textColor: string) => {
  // 水印文字，父元素，字体，文字颜色
  let can: HTMLCanvasElement = document.createElement("canvas");
  parentNode.appendChild(can);
  can.width = 205;
  can.height = 140;
  can.style.display = "none";
  let cans = can.getContext("2d") as CanvasRenderingContext2D;
  cans.rotate((-20 * Math.PI) / 180);
  cans.font = font || "16px Microsoft JhengHei";
  cans.fillStyle = textColor || "rgba(180, 180, 180, 0.3)";
  cans.textAlign = "left";
  cans.textBaseline = "Middle" as CanvasTextBaseline;
  cans.fillText(str, can.width / 10, can.height / 2);
  parentNode.style.backgroundImage = "url(" + can.toDataURL("image/png") + ")";
};

const waterMarker = {
  mounted(el: DirectiveBinding, binding: DirectiveBinding) {
    addWaterMarker(binding.value.text, el, binding.value.font, binding.value.textColor);
  }
};

export default waterMarker;