<html>
<head>
<style>
* {
padding: 0;
margin: 0;
}
canvas {
display: block;
margin: 80px auto;
border: 1px solid #ddd;
}
</style>
</head>
<body>
<canvas id="canvas" width="800" height="600"></canvas>
</body>
<script>
var canvas = document.querySelector('#canvas')
var ctx = canvas.getContext('2d')
var timer
ctx.font="30px Arial";
function Ball (x,y,r,t,color) {
this.x = x
this.y =y
this.r = r
this.t = t
this.color = color
}
Ball.prototype.render = function () {
ctx.beginPath();
ctx.fillText('平抛运动', 100,100)
ctx.arc(this.x,this.y ,this.r,0,2*Math.PI);
ctx.fill()
}
Ball.prototype.horizontal = function (vx) {
this.x += vx
}
Ball.prototype.vertical = function (g) {
if (this.y< 500 ) {
var t = this.t
this.t++
this.y = g*t*t + this.y
} else {
clearInterval(timer)
}
}
var ball = new Ball(30, 30, 24, 0.5, '#f90')
console.dir(ctx)
timer = setInterval(function () {
ctx.clearRect(0,0,800,600)
ball.render()
ball.horizontal(36)
ball.vertical(0.2)
}, 30)
</script>
</html>
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