重力场：地球重力作用的空间。在该空间中，每一点都有惟一的一个重力矢量与之相对应。
各种网络游戏，不管是3D的还是第一视角的，或者横版游戏（如冒险岛），模拟一个重力场是必须的。
先回顾一下谷歌在牛顿诞辰，logo换成了自由落体的苹果。
<html>
<script language="javascript">
var h = 0, v = 1;
window.setTimeout(aa, 2000);
function aa() {
var i = self.setInterval("bb()", 25);
}
function bb() {
var f = document.getElementById('fall');
var r = parseInt(f.style.right) + h;
var b = parseInt(f.style.bottom) - v;
f.style.right = r + 'px';
f.style.bottom = b + 'px';
if (b > -210) {
v += 2;
} else {
h = (v > 9) ? v * 0.1 : 0;
v *= (v > 9) ? -0.3 : 0;
}
}
</script>
<body>
<div id="fall" style="position: relative; right: -300px; bottom: -46px">
apple
</div>
</body>
</html>
<script language="javascript">
var h = 0, v = 1;
window.setTimeout(aa, 2000);
function aa() {
var i = self.setInterval("bb()", 25);
}
function bb() {
var f = document.getElementById('fall');
var r = parseInt(f.style.right) + h;
var b = parseInt(f.style.bottom) - v;
f.style.right = r + 'px';
f.style.bottom = b + 'px';
if (b > -210) {
v += 2;
} else {
h = (v > 9) ? v * 0.1 : 0;
v *= (v > 9) ? -0.3 : 0;
}
}
</script>
<body>
<div id="fall" style="position: relative; right: -300px; bottom: -46px">
apple
</div>
</body>
</html>
可以看到setTimeout和setInterval！不去仔细琢磨逻辑，光从代码语意上，是非常令人费解的。
在没有口语编程之前，我非常想把代码写成这样：
<html>
<script language="javascript">
function drop() {
//自由落体
code here
//撞击地面之后
code here
//苹果摔烂
code here
}
</script>
<body>
<div id="fall" style="position: relative; right: -300px; bottom: -46px">
apple
</div>
<script language="javascript">
<script language="javascript">
function drop() {
//自由落体
code here
//撞击地面之后
code here
//苹果摔烂
code here
}
</script>
<body>
<div id="fall" style="position: relative; right: -300px; bottom: -46px">
apple
</div>
<script language="javascript">
drop();
</script>
</body>
</html>
</script>
</body>
</html>
也只有这样的代码才能调用以后的口语编程接口！那么怎么才能写出这样漂亮的代码？
这个时候【jxcex】 闪亮登场！
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>Jscex Animation</title>
<script language="javascript" type="text/javascript" src="lib/uglifyjs-parser.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.builderBase.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.async.js"></script>
<!--[if IE]>
<script language="javascript" type="text/javascript" src="http://www.cnblogs.com/lib/json2.js"></script>
<script language="javascript">
Jscex.config.codeGenerator = function (code) { return "false || " + code; }
</script>
<![endif]-->
<script type="text/javascript">
var dropAsync = eval(Jscex.compile("async", function (e, startPos, speedY, duration) {
$await(Jscex.Async.sleep(2000));
//e.style.left = startPos.x;
//重力加速度
var g = 50;
var time = 0;
var tag = 0;
while (time < duration) {
$await(Jscex.Async.sleep(25));
if (time < 800) {
//自由落体
time = time + 50;
speedY = speedY + g;
startPos.y += speedY * 0.05;
e.style.top = startPos.y;
}
else {
//撞击地面
if (speedY > 0 && tag == 0) {
tag = 1;
speedY = -speedY;
speedY = speedY / 3;
}
time = time + 50;
speedY = speedY + g;
startPos.y += speedY * 0.05;
e.style.top = startPos.y;
}
}
}));
var changeImageAsync = eval(Jscex.compile("async", function () {
document.getElementById("heart").src = "grieve.gif";
}));
var executeAsync = eval(Jscex.compile("async", function () {
//自由落体并撞击地面
$await(dropAsync(document.getElementById("dropBox"), { x: 0, y: 20 }, 0, 1350));
//❤碎
$await(changeImageAsync());
}));
</script>
</head>
<body>
<div id="dropBox" style="position: absolute; top: 20;">
<img id="heart" src="heart.gif" alt="" />
</div>
<script type="text/javascript">
executeAsync().start();
</script>
</body>
</html>
<html>
<head>
<title>Jscex Animation</title>
<script language="javascript" type="text/javascript" src="lib/uglifyjs-parser.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.builderBase.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.async.js"></script>
<!--[if IE]>
<script language="javascript" type="text/javascript" src="http://www.cnblogs.com/lib/json2.js"></script>
<script language="javascript">
Jscex.config.codeGenerator = function (code) { return "false || " + code; }
</script>
<![endif]-->
<script type="text/javascript">
var dropAsync = eval(Jscex.compile("async", function (e, startPos, speedY, duration) {
$await(Jscex.Async.sleep(2000));
//e.style.left = startPos.x;
//重力加速度
var g = 50;
var time = 0;
var tag = 0;
while (time < duration) {
$await(Jscex.Async.sleep(25));
if (time < 800) {
//自由落体
time = time + 50;
speedY = speedY + g;
startPos.y += speedY * 0.05;
e.style.top = startPos.y;
}
else {
//撞击地面
if (speedY > 0 && tag == 0) {
tag = 1;
speedY = -speedY;
speedY = speedY / 3;
}
time = time + 50;
speedY = speedY + g;
startPos.y += speedY * 0.05;
e.style.top = startPos.y;
}
}
}));
var changeImageAsync = eval(Jscex.compile("async", function () {
document.getElementById("heart").src = "grieve.gif";
}));
var executeAsync = eval(Jscex.compile("async", function () {
//自由落体并撞击地面
$await(dropAsync(document.getElementById("dropBox"), { x: 0, y: 20 }, 0, 1350));
//❤碎
$await(changeImageAsync());
}));
</script>
</head>
<body>
<div id="dropBox" style="position: absolute; top: 20;">
<img id="heart" src="heart.gif" alt="" />
</div>
<script type="text/javascript">
executeAsync().start();
</script>
</body>
</html>
Jquery的animate可以用来制作一些动画效果，但仅限于匀速的直线运动，或者匀速的渐变，当然你可以用下面这种费解的方式去实现变速运动，而且要通过大量的计算才能减少与真实运动的差别。
var i =0 ;
var time = 0;
var z = 100;
function drop() {
if (time <7000) {
i += 5;
z -=1;
$(".block").animate({ top: i }, z);
time += 50;
drop();
}
}
var time = 0;
var z = 100;
function drop() {
if (time <7000) {
i += 5;
z -=1;
$(".block").animate({ top: i }, z);
time += 50;
drop();
}
}
如果是抛物线呢？对于这种变速运动Jquery的animate真是力不从心啊！
如果不用【jxcex】 ,你会陷入一大堆回调循环当中，痛不欲生！当然如果你觉得很爽，你能想明白，又不想让别人看明白，那又是另外一回事了。
不过话说----代码是写给别人看的。
【代码示例下载】：
最新的【jxcex】 库，请上https://github.com/JeffreyZhao/jscex或者http://www.sndacode.com/projects/jscex/wiki下载吧····