一、思路
- 有一个不停画球的方法
- 鼠标移入的时候球开始画,这个时候速度不断变化,当去了边界的时候速度变反
- 鼠标移走停止画图
二、代码
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>ball</title> </head> <body> <canvas id="canvas" width="600" height="300"></canvas> <script> var canvas = document.getElementById('canvas'); var ctx = canvas.getContext('2d'); var raf; var ball = { x: 100, y: 100, vx: 5, vy: 2, radius: 25, color: 'blue', draw: function() { ctx.beginPath(); ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true); ctx.closePath(); ctx.fillStyle = this.color; ctx.fill(); } }; function draw() { // 清楚画布上图形 // ctx.clearRect(0,0, canvas.width, canvas.height); // 不清楚 半透明 ctx.fillStyle = 'rgba(255,255,255,0.3)'; ctx.fillRect(0,0,canvas.width,canvas.height); if (ball.y + ball.vy > canvas.height || ball.y + ball.vy < 0) { ball.vy = -ball.vy; } if (ball.x + ball.vx > canvas.width || ball.x + ball.vx < 0) { ball.vx = -ball.vx; } ball.draw(); ball.x += ball.vx; ball.y += ball.vy; ball.vy *= .99; ball.vy += .25; raf = window.requestAnimationFrame(draw); } canvas.addEventListener('mouseover', function(e){ raf = window.requestAnimationFrame(draw); }); canvas.addEventListener('mouseout', function(e){ window.cancelAnimationFrame(raf); }); ball.draw(); </script> </body> </html>