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canvas.html
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width,initial-scale=1,user-scalable=0">
<meta name="renderer" content="webkit">
<title>Canvas 绘图</title>
<meta name="description" content="首页描述"/>
<meta name="keywords" content="首页关键词"/>
<meta name="author" content="Web Layout:amu"/>
<meta name="format-detection" content="telephone=no,date=no,address=no,email=no,url=no"/>
<link rel="stylesheet" href="./src/style/base.css">
<style>
#canvas{
border: 1px seagreen dashed;transform-origin: 0 0;
width: 800px;height: 400px;max-width: 100%;
box-sizing: border-box;
}
#canvas:hover{cursor :url(assets/images/draw.ico) 0 28,auto;}
#save_href{display: none;}
#outimg{z-index: 10;top:15%}
#outimg img{max-width: 100%;border: 1px dashed #ccc;}
</style>
</head>
<body>
<div class="paper">
<h1>Canvas</h1>
<hr>
<h2>案例：手绘（支持high DPI）</h2>
<p>
<button id="clear">清空</button>
<button id="save">生成图片</button>
<button id="replay">回放</button>
</p>
<canvas id="canvas" width="600" height="400"></canvas>
<br>
<a download="mydraw.png" id="save_href">下载</a>
<span id="touchSize"></span>
<dialog id="outimg">
<br>
<img src="" alt="">
<p class="center">长按图片下载 <button id="btnClose">关闭</button></p>
</dialog>
</div>
</body>
<script type="module">
import canvasdpr from './src/js/canvas.hdpr.js'
let canvas=document.getElementById("canvas");
let strokeCache = []
let index = 1;
let steps = []
let stepIndex = 0
let ctx=canvasdpr(canvas);
let touchSize = document.querySelector('#touchSize')
function drawInit(evt){
let startPoint =[evt.clientX-canvas.offsetLeft,evt.clientY-canvas.offsetTop]
ctx.beginPath();
ctx.lineCap="round";
ctx.shadowBlur=1.4;
ctx.shadowColor="#234";
ctx.moveTo(startPoint[0],startPoint[1]);
strokeCache.push(startPoint)
}
canvas.onmousedown=function(event){
drawInit(event)
document.addEventListener('mousemove',drawFree)
};
function clearCanvas (){
ctx.clearRect(0,0,ctx.canvas.width,ctx.canvas.height)
strokeCache = []
index = 1;
steps = []
stepIndex = 0
btnReplay.disabled = true
btnSave.disabled = true
btnClear.disabled = true
}
function drawFree(evt){
evt.preventDefault();
evt.stopPropagation();
if(!evt.clientX){
console.log(evt)
touchSize.innerHTML = evt.targetTouches[0].radiusX+'-'+evt.targetTouches[0].force //force[0.1~1]
evt.clientX = evt.targetTouches[0].clientX
evt.clientY = evt.targetTouches[0].clientY
}
let point =[evt.clientX-canvas.offsetLeft,evt.clientY-canvas.offsetTop]
ctx.lineTo(point[0],point[1]);
ctx.lineWidth = 6;
ctx.strokeStyle="#234";
ctx.stroke();
strokeCache.push(point)
}
function rePlay(){
ctx.clearRect(0,0,ctx.canvas.width,ctx.canvas.height)
index = 1
stepIndex = 0
ctx.beginPath();
ctx.lineWidth = 6;
ctx.strokeStyle="#234";
console.log(strokeCache)
ctx.moveTo(strokeCache[0][0],strokeCache[0][1])
renderDrawing()
}
function renderDrawing(){
if(index === steps[stepIndex]){
stepIndex ++
ctx.beginPath();
}
ctx.lineTo(strokeCache[index][0],strokeCache[index][1])
ctx.stroke();
if(index<strokeCache.length-1){
index++
requestAnimationFrame(renderDrawing)
}else{
ctx.closePath();
}
}
function drawEnd(){
ctx.closePath();
console.log(strokeCache)
steps.push(strokeCache.length)
if(strokeCache.length>1){
btnReplay.disabled = false
btnSave.disabled = false
btnClear.disabled = false
}
document.removeEventListener('mousemove',drawFree);
}
canvas.onmouseup=function(){
drawEnd()
};
//移动端兼容
canvas.addEventListener('touchstart',(e)=>{
drawInit(e)
canvas.addEventListener('touchmove',drawFree)
})
canvas.addEventListener('touchend',drawEnd)
let btnClear = document.querySelector('#clear')
let btnSave = document.querySelector('#save')
let btnReplay = document.querySelector('#replay')
let btnClose = document.querySelector('#btnClose')
let outDialog = document.querySelector("#outimg")
btnReplay.disabled = true
btnSave.disabled = true
btnClear.disabled = true
btnClear.addEventListener('click',clearCanvas)
btnSave.addEventListener('click',saveCanvas)
btnReplay.addEventListener('click',rePlay)
btnClose.addEventListener('click',closeDialog)
function saveCanvas(){
ctx.save()
let image = new Image()
image.src = canvas.toDataURL("image/png")
if(/Android|webOS|iPhone|iPod|BlackBerry/i.test(navigator.userAgent)){
outDialog.open = true
outDialog.querySelector('img').src=image.src
}else{
let svaeHref = document.querySelector('#save_href')
svaeHref.style.display = 'inline-block'
svaeHref.href=image.src;
}
}
function closeDialog(){
outDialog.open = false
}
</script>
</html>