var nDots = 12;
var Xpos = 0;
var Ypos = 0;

var DELTAT = .01;
var SEGLEN = 10;
var SPRINGK = 10;
var MASS = 1;
var GRAVITY = 40;
var RESISTANCE = 12;
var STOPVEL = 0.1;
var STOPACC = 0.1;
var DOTSIZE = 20;
var BOUNCE = 0.75;
var isNetscape = navigator.appName=="Netscape";
var followmouse = true;
var dots = new Array();

function mvsnake() {
   init();
   if (isNetscape) {
      document.captureEvents(Event.MOUSEMOVE);
      document.onMouseMove = MoveHandler;
   } else {
      document.onmousemove = MoveHandlerIE;
   }
}

function init() {
   var i = 0;
   for (i = 0; i < nDots; i++) {
      dots[i] = new dot(i);
   }
   if (!isNetscape) {
// I only know how to read the locations of the 
// <LI> items in IE
// skip this for now
// setInitPositions(dots)
   }
   for (i = 0; i < nDots; i++) {
      dots[i].obj.left = dots[i].X;
      dots[i].obj.top = dots[i].Y;
   }
   if (isNetscape) {
      startanimate();
   } else {
      // let dots sit there for a few seconds since they're hiding on the real bullets
//      setTimeout("startanimate()", 3000);       // 3秒で startanimate() を実行
      setTimeout("startanimate()", 30);       // 3秒で startanimate() を実行
   }
}

function dot(i) {
   this.X = Xpos;
   this.Y = Ypos;
   this.dx = 0;
   this.dy = 0;
   if (isNetscape) {
      this.obj = eval("document.dot" + i);
   } else {
      this.obj = eval("dot" + i + ".style");
   }
}

function startanimate() {	
   setInterval("animate()", 20);      // 0.02秒で animate() を実行
}

function setInitPositions(dots) {
   var startloc = document.all.tags("LI");
   var i = 0;
   for (i = 0; i < startloc.length && i < (nDots - 1); i++) {
      dots[i+1].X = startloc[i].offsetLeft
      startloc[i].offsetParent.offsetLeft - DOTSIZE;
      dots[i+1].Y = startloc[i].offsetTop +
      startloc[i].offsetParent.offsetTop + 2*DOTSIZE;
   }
   dots[0].X = dots[1].X;
   dots[0].Y = dots[1].Y - SEGLEN;
}

function MoveHandler(e) {
   Xpos = e.pageX;
   Ypos = e.pageY;	  
   return true;
}

function MoveHandlerIE() {
   Xpos = window.event.x + document.body.scrollLeft;
   Ypos = window.event.y + document.body.scrollTop;	  
}

function vec(X, Y) {
   this.X = X;
   this.Y = Y;
}

// adds force in X and Y to spring for dot[i] on dot[j]
function springForce(i, j, spring) {
   var dx = (dots[i].X - dots[j].X);
   var dy = (dots[i].Y - dots[j].Y);
   var len = Math.sqrt(dx*dx + dy*dy);
   if (len > SEGLEN) {
      var springF = SPRINGK * (len - SEGLEN);
      spring.X += (dx / len) * springF;
      spring.Y += (dy / len) * springF;
   }
}

function animate() {	
   var start = 0;
   if (followmouse) {
      dots[0].X = Xpos;
      dots[0].Y = Ypos;
      start = 1;
   }
   for (i = start ; i < nDots; i++ ) {
      var spring = new vec(0, 0);
      if (i > 0) {
         springForce(i-1, i, spring);
      }
      if (i < (nDots - 1)) {
         springForce(i+1, i, spring);
      }
      var resist = new vec(-dots[i].dx * RESISTANCE, -dots[i].dy * RESISTANCE);
      var accel = new vec((spring.X + resist.X)/ MASS, (spring.Y + resist.Y)/ MASS + GRAVITY);
      dots[i].dx += (DELTAT * accel.X);
      dots[i].dy += (DELTAT * accel.Y);
      if (Math.abs(dots[i].dx) < STOPVEL &&
         Math.abs(dots[i].dy) < STOPVEL &&
         Math.abs(accel.X) < STOPACC &&
         Math.abs(accel.Y) < STOPACC) {
            dots[i].dx = 0;
            dots[i].dy = 0;
         }
      dots[i].X += dots[i].dx;
      dots[i].Y += dots[i].dy;
      var height, width;
      if (isNetscape) {
         height = window.innerHeight + document.scrollTop;
         width = window.innerWidth + document.scrollLeft;
      } else {	
         height = document.body.clientHeight + document.body.scrollTop;
         width = document.body.clientWidth + document.body.scrollLeft;
      }
      if (dots[i].Y >=  height - DOTSIZE - 1) {
         if (dots[i].dy > 0) {
            dots[i].dy = BOUNCE * -dots[i].dy;
         }
         dots[i].Y = height - DOTSIZE - 1;
      }
      if (dots[i].X >= width - DOTSIZE) {
         if (dots[i].dx > 0) {
            dots[i].dx = BOUNCE * -dots[i].dx;
         }
         dots[i].X = width - DOTSIZE - 1;
      }
      if (dots[i].X < 0) {
         if (dots[i].dx < 0) {
            dots[i].dx = BOUNCE * -dots[i].dx;
         }
         dots[i].X = 0;
      }
      dots[i].obj.left = dots[i].X;
      dots[i].obj.top =  dots[i].Y;
   }
}
// End -->