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canvas_3.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<link rel="stylesheet" type="" href="https://at.alicdn.com/t/font_dro5eh6p4ro4j9k9.css">
<style>
* {
margin: 0;
padding: 0;
}
body {
overflow: hidden;
}
#app {
background: #ddd;
display: block;
}
.actions {
position: fixed;
top: 0;
left: 0;
padding: 4px;
width: 100%;
}
.round{
position: absolute;
width: 10px;
height: 10px;
background: darkgrey;
border-radius:5px;
right: 0;
top: 0;
transition-property: opacity;
transition-delay: 0.1s;
}
</style>
</head>
<body>
<div class="actions">
<label><input type="radio" name="penType" value="pen" checked><i class="iconfont icon-pen"></i></label>
<label><input type="radio" name="penType" value="eraser"><i class="iconfont icon-eraser"></i></label>
<button type="" id="save"><i class="iconfont icon-save"></i></button>
</div>
<div class="round">
</div>
<canvas id="app" width="375" height="667"></canvas>
<script>
let previousPoint;
let canvas = document.querySelector('#app')
let clientWidth = document.documentElement.clientWidth;
let clientHeight = document.documentElement.clientHeight
canvas.width = clientWidth;
canvas.height = clientHeight;
let context = canvas.getContext('2d');
let width = canvas.width,height=canvas.height;
if (window.devicePixelRatio) {
canvas.style.width = width + "px";
canvas.style.height = height + "px";
canvas.height = height * window.devicePixelRatio;
canvas.width = width * window.devicePixelRatio;
context.scale(window.devicePixelRatio, window.devicePixelRatio);
}
let r = document.querySelector('.round');
context.fillStyle = "green"
context.strokeStyle = 'green';
canvas.addEventListener('touchstart',function(e){
let {pageX,pageY} = e.touches[0]
r.style.opacity = 1;
r.style.left = pageX - 5 + 'px'
r.style.top = pageY - 5 + 'px'
// round = document.createElement('div')
// round.style.position = 'absolute';
// round.style.top = pageY -5 + "px"
// round.style.left = pageX -5 + "px";
// round.style.height = '10px';
// round.style.width = '10px';
// round.style.opacity = 0.5;
// round.style.borderRadius = '5px';
// round.style.background = "green"
// round.style.transition = "opacity 1s"
// document.body.appendChild(round);
})
canvas.addEventListener('touchmove',function(e){
e.preventDefault();//加入这一句话之后，屏幕都不能缩放了
let penType = document.querySelector('input[type=radio]:checked').value
let {pageX,pageY} = e.touches[0];
r.style.left = pageX - 5 + 'px'
r.style.top = pageY - 5 + 'px'
// context.arc(pageX,pageY,5,0,Math.PI*2,false)
// context.fill()
if(penType === 'pen'){
if(previousPoint){
context.beginPath();
context.moveTo(previousPoint.pageX,previousPoint.pageY)
context.lineTo(pageX,pageY)
context.stroke()
}
previousPoint = {
pageX,pageY
}}else{
context.globalCompositeOperation= 'destination-out'
context.arc(pageX, pageY, 20, 0, Math.PI*2, true);
context.fill();
}
// previousPoint = {
// pageX:pageX,
// pageY:pageY
// }
})
canvas.addEventListener('touchend',function(e){
previousPoint = null;
r.style.opacity = 0;
})
save.onclick = function(){
var canvas = document.getElementById('app');
var data = canvas.toDataURL('image/png');
var newWindow = window.open('about:blank','image from canvas');
newWindow.document.write('<img src=' + `'${data}'` + ' alt = from canvas />')
}
// canvas.addEventListener('touchmove',function(e){
// let {pageX,pageY} = e.touches[0];
// context.beginPath();
// context.moveTo(pageX,pageY);
// })
// context.fillstyle = "green";
// context.strokestyle = "blue";
// context.beginPath()
// context.moveTo(75,50);
// context.lineTo(100,75);
// context.lineTo(100,25);
// context.lineTo(75,50);
// context.stroke();
</script>
</body>
</html>