JavaScript拖拽、碰撞、重力及弹性运动实例分析

window.onload=function (){ var oDiv=document.getElementById('div1'); var lastX=0; var lastY=0; oDiv.onmousedown=function (ev) { var oEvent=ev||event; var disX=oEvent.clientX-oDiv.offsetLeft; var disY=oEvent.clientY-oDiv.offsetTop; document.onmousemove=function (ev) {  var oEvent=ev||event;  var l=oEvent.clientX-disX;  var t=oEvent.clientY-disY;  oDiv.style.left=l+'px';  oDiv.style.top=t+'px';  iSpeedX=l-lastX;  iSpeedY=t-lastY;  lastX=l;  lastY=t;  document.title='x:'+iSpeedX+', y:'+iSpeedY; }; document.onmouseup=function () {  document.onmousemove=null;  document.onmouseup=null;  startMove(); }; clearInterval(timer); };};var timer=null;var iSpeedX=0;var iSpeedY=0;function startMove(){ clearInterval(timer); timer=setInterval(function (){ var oDiv=document.getElementById('div1'); iSpeedY+=3; var l=oDiv.offsetLeft+iSpeedX; var t=oDiv.offsetTop+iSpeedY; if(t>=document.documentElement.clientHeight-oDiv.offsetHeight) {  iSpeedY*=-0.8;  iSpeedX*=0.8;  t=document.documentElement.clientHeight-oDiv.offsetHeight; } else if(t<=0) {  iSpeedY*=-1;  iSpeedX*=0.8;  t=0; } if(l>=document.documentElement.clientWidth-oDiv.offsetWidth) {  iSpeedX*=-0.8;  l=document.documentElement.clientWidth-oDiv.offsetWidth; } else if(l<=0) {  iSpeedX*=-0.8;  l=0; } if(Math.abs(iSpeedX)<1) {  iSpeedX=0; } if(Math.abs(iSpeedY)<1) {  iSpeedY=0; } if(iSpeedX==0 && iSpeedY==0 && t==document.documentElement.clientHeight-oDiv.offsetHeight) {  clearInterval(timer);  alert('停止'); } else {  oDiv.style.left=l+'px';  oDiv.style.top=t+'px'; } document.title=iSpeedX; }, 30);}

var left=0; //用left变量存储赋给obj.style.left的值，以防每次系统都省略小数，所导致最后结果的细微差异var iSpeed=0;function startMove(obj,iTarget){ clearInterval(obj.timer); obj.timer=setInterval(function(){  iSpeed+=(iTarget-obj.offsetLeft)/5; //速度  iSpeed*=0.7; //考虑阻力  left+=iSpeed;  if(Math.abs(iSpeed)<1&&Math.abs(iTarget-obj.offsetLeft)<1) //停止条件 速度和距离绝对值小于1  {   clearInterval(obj.timer);   obj.style.left=iTarget+"px"; //清楚后，顺便把目标值赋给obj.style.left  }   else  {   obj.style.left=left+"px";  } },30);}