本文實例講述了js+html5實現的自由落體運動效果。分享給大家參考，具體如下：
運作效果截圖如下：
具體程式碼如下：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>canvas自由落体</title>
<script type="text/javascript" >
var canvasheight = 500;
var canvaswidth = 500;
var g = 9.8;
var plusV = 0.5;
function Block(vo, x, y, width, height, g, context) {
var _self = this;
_self.vo = vo || 0;
_self.x = x;
_self.y = y;
_self.prevX = x;
_self.prevY = y;
_self.g = g;
_self.height = height;
_self.width = width;
_self.prevTime = new Date().getTime();
context.fillStyle = "black";
_self.down = function () {
var time = (new Date().getTime() - _self.prevTime) / 200,
y = _self.vo * time + 1 / 2 * _self.g * time * time + _self.y;
//console.log("down:time=" + time + ":y=" + y + ":" + _self.vo);
if (y + _self.height >= canvasheight) {
_self.g--;
_self.vo = _self.g * time;
_self.prevTime = new Date().getTime();
_self.up();
} else {
context.clearRect(_self.prevX, _self.prevY - 1, _self.prevX + _self.height, _self.prevY + _self.width);
context.fillRect(_self.x, y, _self.width, _self.height);
_self.prevX = x;
_self.prevY = y;
setTimeout(function () {
_self.down();
}, 30);
}
}
_self.up = function () {
var time = (new Date().getTime() - _self.prevTime) / 200,
v = _self.vo - _self.g * time,
y = canvasheight - _self.height - _self.vo * time + 1 / 2 * _self.g * time * time;
//console.log("up:time=" + time + ":v=" + v);
if (v <= 0) {
_self.vo = 0;
_self.y = y;
_self.prevTime = new Date().getTime();
if (y + _self.height < canvasheight) {
_self.down();
} else {
return;
}
} else {
context.clearRect(_self.prevX, _self.prevY - 1, _self.prevX + _self.height , _self.prevY + _self.width);
context.fillRect(x, y, _self.width, _self.height);
_self.prevX = x;
_self.prevY = y;
setTimeout(function () {
_self.up();
}, 30);
}
}
}
window.onload = function () {
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
height = canvas.offsetHeight;
var block = new Block(0, 100, 0, 20, 20, g, context);
block.down();
}
</script>
</head>
<body>
<center>
<canvas id="canvas" width="500" height="500" style="background:#DDDDDD" ></canvas>
</center>
<input type="button" value="stop" onclick="stop()" />
<input type="button" value="start" onclick="start()" />
</body>
</html>
更多關於JavaScript運動相關內容有興趣的讀者可查看本站專題：《JavaScript運動效果與技巧匯總》
希望本文所述對大家JavaScript程式設計有所幫助。
