index.html
<!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>Document</title>
<link rel="stylesheet" href="./style.css">
</head>
<body>
<!-- <div id="canvas"></div> -->
<canvas id="canvas" width="100" height="100"></canvas>
</body>
<script type="text/javascript" src="./index.js"></script>
</html>
index.js
// 存在画线卡顿问题
// var canvas = document.getElementById('canvas')
// console.log('canvas',canvas)
// // canvas.onclick = (e) => {
// canvas.onmousemove = (e) => {
// console.log(e.clientX)
// console.log(e.clientY)
// // console.log 调试大法
// let div = document.createElement('div')
// div.style.position = 'absolute'
// div.style.left = e.clientX + 'px'
// div.style.top = e.clientY + 'px'
// // div.style.border = '1px solid red'
// div.style.width = '6px'
// div.style.height = '6px'
// div.style.marginLeft = '-3px'
// div.style.marginTop = '-3px'
// div.style.borderRadius = '50%'
// div.style.backgroundColor = 'black'
// canvas.appendChild(div)
// }
// 改为使用canvas
//画线
let canvas = document.getElementById("canvas");
// 获取浏览器窗口文档显示区域的宽度，不包括滚动条。
canvas.width = document.documentElement.clientWidth
// 获取浏览器窗口文档显示区域的高度，不包括滚动条。
canvas.height = document.documentElement.clientHeight
let ctx = canvas.getContext("2d");
ctx.fillStyle = "black"
ctx.strokeStyle = "none"
ctx.lineWidth = 8
ctx.lineCap = "round"
let painting = false
let last
let isTouchDevice = 'ontouchstart' in document.documentElement;
// console.log(isTouchDevice)
if (isTouchDevice) {
canvas.ontouchstart = (e) => {
let x = e.touches[0].clientX
let y = e.touches[0].clientY
last = [x, y]
}
canvas.ontouchmove = (e) => {
let x = e.touches[0].clientX
let y = e.touches[0].clientY
// ctx.beginPath();
// ctx.arc(x, y, 10, 0, 2 * Math.PI);
// ctx.stroke();
// ctx.fill()
drawLine(last[0], last[1], x, y)
last = [x, y]
}
} else {
canvas.onmousedown = (e) => {
painting = true
last = [e.clientX, e.clientY]
}
canvas.onmousemove = (e) => {
// console.log(e.clientX)
// console.log(e.clientY)
if (painting === true) {
// ctx.fillRect(e.clientX - 5, e.clientY - 5, 10, 10);
// ctx.beginPath();
// ctx.arc(e.clientX, e.clientY, 10, 0, 2 * Math.PI);
// ctx.stroke();
// ctx.fill()
drawLine(last[0], last[1], e.clientX, e.clientY)
last = [e.clientX, e.clientY]
}
}
canvas.onmouseup = () => {
painting = false
}
}
function drawLine(x1, y1, x2, y2) {
ctx.beginPath();
ctx.moveTo(x1, y1)
ctx.lineTo(x2, y2)
ctx.stroke();
}
style.css
* {
margin: 0;
padding:0;
box-sizing: border-box;
}
body {
overflow: hidden;
}
#canvas {
/* 跟屏幕一样高 */
/* height: 100vh; */
/* 跟屏幕一样宽 */
/* width: 100vw; */
/* border: 1px solid red; */
/* canvas默认是inline元素 */
/* display: block; */
display: block;
}
github：mianxiong.github.io/canvas/inde…
资料来源：饥人谷
