• canvas画布绘图

    请添加图片描述

    DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Documenttitle>
    <style>
      .active {
        color: red;
      }
    style>
  head>

  <body>
    <canvas id="c1" width="800" height="400">canvas>
    <hr />
    <button id="boldBtn">粗线条button>
    <button id="thinBtn">细线条button>
    <button id="saveBtn">保存签名button>
    <button id="downloadBtn">下载签名button>
    <input type="color" id="color" value="" />
    <button id="clearBtn">橡皮擦button>
    <button id="nullBtn">清空画布button>

    <script>
      // 1. 获取canvas画布和绘制的上下文对象
      /** @type {HTMLCanvasElement} */
      var canvas = document.querySelector("#c1");
      var ctx = canvas.getContext("2d");
      // 连接处圆润
      ctx.lineJoin = "round";
      // 开头和结束端圆润
      ctx.lineCap = "round";
      // 2. 获取输入框和按钮
      // 设置画笔的粗细
      var boldBtn = document.querySelector("#boldBtn");
      var thinBtn = document.querySelector("#thinBtn");
      var saveBtn = document.querySelector("#saveBtn");
      var downloadBtn = document.querySelector("#downloadBtn");
      var clearBtn = document.querySelector("#clearBtn");
      var nullBtn = document.querySelector("#nullBtn");
      var inputColor = document.querySelector("#color");
      // 设置允许绘制的变量
      var isDraw = false;

      // 鼠标按下
      canvas.onmousedown = function () {
        isDraw = true;
        ctx.beginPath();
        let x = event.pageX - canvas.offsetLeft;
        let y = event.pageY - canvas.offsetTop;
        ctx.moveTo(x, y);
      };
      // 鼠标离开
      canvas.onmouseleave = function () {
        isDraw = false;
        ctx.closePath();
      };
      // 鼠标抬起
      canvas.onmouseup = function () {
        isDraw = false;
        ctx.closePath();
      };
      // 鼠标移动
      canvas.onmousemove = function () {
        if (isDraw) {
          let x = event.pageX - canvas.offsetLeft;
          let y = event.pageY - canvas.offsetTop;
          ctx.lineTo(x, y);
          ctx.stroke();
        }
      };
      boldBtn.onclick = function () {
        ctx.globalCompositeOperation = "source-over";
        ctx.lineWidth = 20;
        boldBtn.classList.add("active");
        thinBtn.classList.remove("active");
        clearBtn.classList.remove("active");
      };
      thinBtn.onclick = function () {
        ctx.globalCompositeOperation = "source-over";
        ctx.lineWidth = 2;
        thinBtn.classList.add("active");
        boldBtn.classList.remove("active");
        clearBtn.classList.remove("active");
      };
      clearBtn.onclick = function () {
        ctx.globalCompositeOperation = "destination-out";
        ctx.lineWidth = 30;
        clearBtn.classList.add("active");
        boldBtn.classList.remove("active");
        thinBtn.classList.remove("active");
      };
      nullBtn.onclick = function () {
        ctx.clearRect(0, 0, 800, 400);
      };
      // 保存生成图片
      saveBtn.onclick = function () {
        let urlData = canvas.toDataURL();
        let img = new Image();
        img.src = urlData;
        document.body.appendChild(img);
      };
      // 下载画布图片
      downloadBtn.onclick = function () {
        let urlData = canvas.toDataURL();
        let downloadA = document.createElement("a");
        downloadA.setAttribute("download", "签名");
        downloadA.href = urlData;
        downloadA.click();
      };
      // 改变颜色
      inputColor.onchange = function () {
        ctx.strokeStyle = inputColor.value;
      };
    script>
  body>
html>


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  • 原文地址：https://blog.csdn.net/qq_41154522/article/details/127766645