知识点
canvas 的宽高设置
js的使用
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>鼠标滑动泡泡</title>
<meta name="keywords" content="鼠标滑动泡泡">
<meta name="description" content="5月8日，前端复习">
<style type="text/css">
body {margin:0;}
#canvas {
/* background-color:#fff; */
background-color:#222;
display:block;
}
</style>
</head>
<body>
<canvas id="canvas"></canvas>
<script>
var canvas = document.querySelector('#canvas');//选中目标元素
var ctx = canvas.getContext('2d');//生成绘制环境并返回
var ww,hh;
var balllist = [];
function init(){ //浏览器显示页面初始化
canvas.width = ww = window.innerWidth;
canvas.height = hh = window.innerHeight;
}
window.onresize = init; //添加浏览器调整监控事件
init();
function Ball(x,y){
this.x = x;
this.y = y;
this.r = 50;
this.vx = Math.random()*6-3;
this.vy = Math.random()*6-3;
this.c = '#'+Math.floor(Math.random()*1000000);
}
Ball.prototype={
draw:function(ctx){
ctx.beginPath();
ctx.arc(this.x,this.y,this.r,0,Math.PI*2,false); //画圆描述画法 X坐标 Y坐标 R半径 圆的起始点 绘制旋转半径,绘制方形
ctx.fillStyle = this.c;
// ctx.globalCompositeOperation = 'xor'; //使用异或操作对源图像与目标图像进行组合
ctx.globalCompositeOperation = 'lighter'; //显示源图像 + 目标图像
ctx.fill();
},
update:function(){
this.x+=this.vx;
this.y+=this.vy;
this.vy*=0.99;
this.vx*=0.99;
this.r-=0.3;
if(this.r < 0){
this.r = 0;
}
}
}
canvas.addEventListener('mousemove',function(e){
balllist.push(new Ball(e.clientX,e.clientY))//鼠标移动 绘制球的坐标
})
function render(){
ctx.clearRect(0,0,ww,hh);
balllist.forEach(function(ball){
ball.draw(ctx);
ball.update();
})
//判断半径小于0的时候，清除/回收
for(var i=0;i<balllist.length;i++){
if(balllist[i].r==0){
balllist.splice(i,1);
}
}
requestAnimationFrame(render);
}
render();
</script>
</body>
</html>点击 "运行实例" 按钮查看在线实例
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