层的拖动 且 不超过边界

οnmοusedοwn="layerMousedown();" οnmοusemοve="layerMousemove();" οnmοuseup="layerMouseup();"var layerMoveFlag = false;
var x1= 0;
var y1= 0;
function layerMousedown(){
  layerMoveFlag=true;
  var layerMsg = document.getElementById("layerMsg");
  x1=window.event.clientX-layerMsg.offsetLeft;
  y1=window.event.clientY-layerMsg.offsetTop;
}

function layerMousemove(){
  if(layerMoveFlag){
    var mydiv = document.getElementById("layerMsg");
    mydiv.setCapture();
    var X=window.event.clientX;
    var Y=window.event.clientY;
    
    if(Y-y1<0){
      Y=y1
    }
    if(X-x1<0){
      X=x1;
    }
    if((X-x1)>(winWidth-419)){
      X=winWidth-(419-x1);
    }
    if((Y-y1)>(winHeight-205)){
      Y=winHeight-(205-y1);   
    }
        
    mydiv.style.left=X-x1+"px";
    mydiv.style.top =Y-y1+"px";   
  }
}

function layerMouseup(){
  layerMoveFlag=false;
  document.getElementById("layerMsg").releaseCapture();
}

jsp中层的调动：