有个要注意的点,就是canvas标签本身自带width与height属性,设置此属性可以直接更改canvas坐标系的宽与高,而在css里设置宽高,只是把canvas坐标系拉伸了,坐标值不变,显示出来的图像也都被拉伸了。
<html> <body> <canvas id = "canvas" width = "800px" height="600px"></canvas> <script type="text/javascript"> var canvas = document.getElementById("canvas"); var parti = []; function loop() { CreateParticles(); UpdateParticles(); KillParticles(); DrawParticles(); } function CreateParticles() { var partis = {x:Math.random()*canvas.clientWidth, y:0 , color:"white", radius:2 + Math.random()* 5 ,speed:2+Math.random()*5}; if(parti.length < 80) { parti.push(partis); } } function UpdateParticles() { for(var i in parti) { parti[i].y += parti[i].speed; } } function KillParticles() { for(var i in parti) { if(parti[i].y >= canvas.clientHeight) { parti[i].y = 0; } } } function DrawParticles() { var contex = canvas.getContext("2d"); contex.fillStyle = "black"; contex.fillRect(0,0,canvas.clientWidth,canvas.clientHeight); for(var i in parti) { contex.beginPath(); contex.arc(parti[i].x, parti[i].y,parti[i].radius,0,Math.PI * 2); contex.closePath(); contex.fillStyle = parti[i].color; contex.fill(); } } setInterval(loop,30); </script> </body> </html>