关于canvas:canvas添加水印

// 动静尺寸const dynamicDateSize = function (size) {    //return (document.body.offsetWidth / 375) * size;    return (getClientW() / 375) * size}export function addWaterBack(text) {  const width = window.screen.width || document.body.offsetWidth;  const height = window.screen.height || document.body.clientHeight;  let selector = document.querySelector("body");  let section = document.createElement("section");  const styleStr = `        position: fixed;        width: 100%;        height: 100%;        left: 0;        top: 0;        pointer-events: none;        z-index: 199999999;`;  section.setAttribute('style', styleStr);  section.style.background = `url(${_canvasToimg(width, height, text)})`;  //section.classList.add("warter-back");  selector.appendChild(section);  //selector.style.background = `url(${_canvasToimg(width, height, text)})`;}function _canvasToimg(width, height, text) {  const width2 = width / 2;  const height3 = height / 5;  // 单个水印  let sCanvas = document.createElement("canvas"); // 创立canvas标签  sCanvas.width = width2; // 设置画布大小  sCanvas.height = height3;  let ctx = sCanvas.getContext("2d");  ctx.fillStyle = "rgba(35,24,21,0.1)";  const fontSize = Math.min(Number(CommonJs.dynamicDateSize(12)).toFixed(0) || 12, 24);  ctx.font = `${fontSize}px Arial`;  ctx.rotate((-25 * Math.PI) / 180);  ctx.fillText(text, 0, height3 / 1.5);  ctx.rotate((25 * Math.PI) / 180);  // 大的canvas  let bCanvas = document.createElement("canvas");  bCanvas.width = width;  bCanvas.height = height;  let ctx1 = bCanvas.getContext("2d");  ctx1.clearRect(0, 0, width, height);  let pat = ctx1.createPattern(sCanvas, "repeat"); //在指定的方向上反复指定的元素  ctx1.fillStyle = pat;  ctx1.fillRect(0, 0, width, width);  return sCanvas.toDataURL("image/png");}