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canvas2.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-layer{
position: relative;
}
canvas{position: absolute;background: rgba(0,0,0,.2);left: 0;top: 0;}
#canvas{}
#canvas2{border: 1px seagreen dashed;}
</style>
</head>
<body>
<div class="paper">
<h1>Canvas 绘图</h1>
<hr>
<h2>案例一：canvas绘制图形，且位置相对图片固定</h2>
<div class="canvas-layer">
<img width="60%" src="assets/images/map.png" alt="">
<canvas id="canvas1"></canvas>
</div>
<h2>案例一：随机绘制4个线段</h2>
<div class="canvas-layer">
<img width="60%" src="assets/images/map.png" alt="">
<canvas id="canvas"></canvas>
</div>
<button onclick="previewHumanBody(true)">预览</button>
<button onclick="previewHumanBody(false)">禁用预览</button>
<br>
</div>
</body>
<script>
const canvasSetting = {
ctx:''
}
function init(canvas){
let mapImg=canvas.previousElementSibling;
mapImg.onload = (e)=>{
resizeCanvas(mapImg)
previewHumanBody(true)
}
}
function resizeCanvas(imgEl){
canvasSetting.ctx = ctxInit(imgEl)
//drawLine(start,end,scaleX,scaleY)
}
let canvas1=document.getElementById("canvas1");
init(canvas1)
function ctxInit(el){
canvas.width = el.width;
canvas.height = el.height;
let ctx=canvas.getContext("2d");
let scaleX = el.width/el.naturalWidth;
let scaleY = el.height/el.naturalHeight;
let scale = {
x:scaleX,
y:scaleY
}
return ctx
}
let start = {x:351,y:385},end={x:503,y:520};
let humanBodyArray = [[4,105],[141,269],[408,623],[814,1071]]
window.onresize = ()=>{
resizeCanvas(canvas1)
//drawLine(start,end,scaleX,scaleY)
}
function drawLine(start,end,scaleX,scaleY){
ctx.clearRect(0,0,1000,1000)
ctx.beginPath();
ctx.scale(scaleX,scaleY)
ctx.moveTo(start.x,start.y);
ctx.lineTo(end.x,end.y);
ctx.closePath();
ctx.lineWidth = 2;
ctx.setLineDash([5,15]);
ctx.strokeStyle = "red"
ctx.stroke();
}
function poly (num){
let r = 100;
let a = 2 * Math.PI / num;
ctx.beginPath();
ctx.moveTo(150+r,150);
for(let i=0;i < num;i++){
let x = 150 + r * Math.cos(a * i);
let y = 150 + r * Math.sin(a * i);
ctx.lineTo(x,y);
}
ctx.closePath();
ctx.stroke();
}
//poly(8);
function previewHumanBody(show){
ctx = canvasSetting.ctx
ctx.clearRect(0,0,1000,1000)
if(show){
humanBodyArray.forEach((item) => {
let pointX = Math.floor(Math.random()*(canvas.width - 1 + 1) + 1)
let pointObj = {
start:{
x:pointX,
y:item[0]
},
end:{
x:pointX,
y:item[1]
}
}
insertLines(ctx,pointObj.start,pointObj.end,"#cc0000");
});
}
}
function insertLines(ctx,startPoint,endPoint,color){
//console.log(startPoint,endPoint,color,scale)
ctx.beginPath();
//ctx.scale(scale.x,scale.y)
ctx.moveTo(startPoint.x, startPoint.y);
ctx.lineTo(endPoint.x, endPoint.y);
ctx.strokeStyle = color;
ctx.lineWidth = 6;
ctx.lineCap="round";
ctx.stroke();
}
// let videoDom2=document.getElementById("video");
// let canvas2=document.getElementById("canvas");
// let ctx2=canvas.getContext("2d");
// let start = {x:351,y:385},end={x:503,y:520};
// videoDom2.onload = ()=>{
// let scaleX = videoDom2.width/originalVideo.width;
// let scaleY = videoDom2.height/originalVideo.height;
// canvas.width = videoDom2.width;
// canvas.height = videoDom2.height;
// drawLine(start,end,scaleX,scaleY)
// }
// window.onresize = ()=>{
// let scaleX = videoDom.width/originalVideo.width;
// let scaleY = videoDom.height/originalVideo.height;
// canvas.width = videoDom.width;
// canvas.height = videoDom.height;
// drawLine2(start,end,scaleX,scaleY)
// }
// function drawLine2(start,end,scaleX,scaleY){
// ctx.clearRect(0,0,1000,1000)
// ctx.beginPath();
// ctx.scale(scaleX,scaleY)
// ctx.moveTo(start.x,start.y);
// ctx.lineTo(end.x,end.y);
// ctx.closePath();
// ctx.lineWidth = 2;
// ctx.setLineDash([5,15]);
// ctx.strokeStyle = "red"
// ctx.stroke();
// }
</script>
</html>