碰撞运动

 1     window.onload = startMove;
 2     
 3     var iSpeedX = 100;
 4     var iSpeedY = 8;
 5 
 6     function startMove() {
 7         setInterval(function() {
 8             var oDiv = document.getElementById("div1");
 9 
10             //加重力
11             iSpeedY += 5;
12 
13             var l = oDiv.offsetLeft + iSpeedX;
14             var t = oDiv.offsetTop + iSpeedY;
15 
16             //防止出界
17             if (l >= document.documentElement.clientWidth - oDiv.offsetWidth) {
18                 iSpeedX *= -0.8;
19                 l = document.documentElement.clientWidth - oDiv.offsetWidth;
20             } else if (l <= 0) {
21                 iSpeedX *= -0.8;
22                 l = 0;
23             }
24 
25             if (t >= document.documentElement.clientHeight - oDiv.offsetHeight) {
26                 iSpeedY *= -0.8;
27                 iSpeedX *= 0.8;
28                 t = document.documentElement.clientHeight - oDiv.offsetHeight;
29             } else if (t <= 0) {
30                 iSpeedY *= -0.8;
31                 iSpeedX *= 0.8;
32                 t = 0;
33             }
34 
35             //解决小数为负数不停止滑动的问题
36             if (Math.abs(iSpeedX) < 1) {
37                 iSpeedX = 0;
38             }
39 
40             if (Math.abs(iSpeedY) < 1) {
41                 iSpeedY = 0;
42             }
43 
44             oDiv.style.left = l + "px";
45             oDiv.style.top = t + "px";
46         }, 30);
47     }

 1     window.onload = function() {
 2         var oDiv = document.getElementById("div1");
 3         var lastX = 0;
 4         var lastY = 0;
 5 
 6         oDiv.onmousedown = function(ev) {
 7             clearInterval(timer);
 8 
 9             var oEvent = ev || event;
10             var disX = oEvent.clientX - oDiv.offsetLeft;
11             var disY = oEvent.clientY - oDiv.offsetTop;
12 
13             document.onmousemove = function(ev) {
14                 var oEvent = ev || event;
15 
16                 var l = oEvent.clientX - disX;
17                 var t = oEvent.clientY - disY;
18 
19                 oDiv.style.left = l + "px";
20                 oDiv.style.top = t + "px";
21 
22                 //计算时刻位移来获取速度
23                 iSpeedX = l - lastX;
24                 iSpeedY = t - lastY;
25 
26                 lastX = l;
27                 lastY = t;
28             };
29 
30             document.onmouseup = function() {
31                 document.onmousemove = null;
32                 document.onmouseup = null;
33                 startMove();
34             };
35         };
36     };
37     var timer = null;
38     var iSpeedX = 0;
39     var iSpeedY = 0;
40 
41     function startMove() {
42         clearInterval(timer);
43         timer = setInterval(function() {
44             var oDiv = document.getElementById("div1");
45 
46             //加重力
47             iSpeedY += 5;
48 
49             var l = oDiv.offsetLeft + iSpeedX;
50             var t = oDiv.offsetTop + iSpeedY;
51 
52             //防止出界
53             if (l >= document.documentElement.clientWidth - oDiv.offsetWidth) {
54                 iSpeedX *= -0.8;
55                 l = document.documentElement.clientWidth - oDiv.offsetWidth;
56             } else if (l <= 0) {
57                 iSpeedX *= -0.8;
58                 l = 0;
59             }
60 
61             if (t >= document.documentElement.clientHeight - oDiv.offsetHeight) {
62                 iSpeedY *= -0.8;
63                 iSpeedX *= 0.8;
64                 t = document.documentElement.clientHeight - oDiv.offsetHeight;
65             } else if (t <= 0) {
66                 iSpeedY *= -0.8;
67                 iSpeedX *= 0.8;
68                 t = 0;
69             }
70 
71             //解决小数为负数不停止滑动的问题
72             if (Math.abs(iSpeedX) < 1) {
73                 iSpeedX = 0;
74             }
75 
76             if (Math.abs(iSpeedY) < 1) {
77                 iSpeedY = 0;
78             }
79 
80             //运动终止条件
81             if (iSpeedX == 0 && iSpeedY == 0 
82                 && t == document.documentElement.clientHeight - oDiv.offsetHeight) {
83                 clearInterval(timer);
84             } else {
85                 oDiv.style.left = l + "px";
86                 oDiv.style.top = t + "px";
87             }
88         }, 30);
89     }