// mousetrl.js
//###############################################################################
/*
 *Elastic Trail script (By Philip Winston @ pwinston@yahoo.com, URL:http://members.xoom.com/ebullets)
 *Script featured on Dynamicdrive.com
 *For this and 100's more DHTML scripts, visit http://dynamicdrive.com
*/


// Thanks to Troels Jakobsen <tjak@get2net.dk>
// for fix which makes it work when the page is scrolled
//###############################################################################

var nDots = 7;

if (document.all && window.print)
{
	document.body.style.cssText = "overflow-x:hidden;overflow-y:scroll";
}

var Xpos = 0;
var Ypos = 0;

  // FIXED TIME STEP, NO RELATION TO REAL TIME
var DELTAT = .01;
  // SIZE OF ONE SPRING IN PIXELS
var SEGLEN = 10;
  // SPRING CONSTANT, STIFFNESS OF SPRINGS
var SPRINGK = 10;
  // ALL THE PHYSICS IS BOGUS, JUST PICKED STUFF TO
  // MAKE IT LOOK OKAY
var MASS = 1;
var GRAVITY = 50;
var RESISTANCE = 10;
  // STOPPING CRITEREA TO PREVENT ENDLESS JITTERING
  // DOESN'T WORK WHEN SITTING ON BOTTOM SINCE FLOOR
  // DOESN'T PUSH BACK SO ACCELERATION ALWAYS AS BIG
  // AS GRAVITY
var STOPVEL = 0.1;
var STOPACC = 0.1;
var DOTSIZE = 11;
  // BOUNCE IS PERCENT OF VELOCITY RETAINED WHEN 
  // BOUNCING OFF A WALL
var BOUNCE = 0.75;

var isNetscape = (navigator.appName == "Netscape");


  // ALWAYS ON FOR NOW, COULD BE PLAYED WITH TO
  // LET DOTS FALL TO BOTTON, GET THROWN, ETC.
var followmouse = false;

var dots = new Array();

initFeet();

function SwitchFeet()
{
	if (followmouse == true)
	{
		document.frmAnimation.btnFeet.value = 'Foot Pursuit';
		followmouse = false;
	}
	else
	{
		document.frmAnimation.btnFeet.value = 'Stop Pursuit';
		followmouse = true;
	}
}

function initFeet()
{
    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)
    }
    
    // SET THEIR POSITIONS
    for (i = 0; i < nDots; i++) 
	{
        dots[i].obj.left = dots[i].X;
        dots[i].obj.top = dots[i].Y;
    }
    
    
    if (isNetscape) 
	{
        // START RIGHT AWAY SINCE THEY ARE POSITIONED
        // AT 0, 0
        StartAnimation();
    } 
	else 
	{
        // LET DOTS SIT THERE FOR A FEW SECONDS
        // SINCE THEY'RE HIDING ON THE REAL BULLETS
        setTimeout("StartAnimation()", 2000);
    }
}

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 StartAnimation() 
{	
    setInterval("Animate()", 20);
}


// THIS IS TO LINE UP THE BULLETS WITH ACTUAL <LI> TAGS ON THE PAGE
// HAD TO ADD -dotsize TO x AND 2*dotsize TO y FOR IE 5, NOT SURE WHY
// STILL DOESN'T WORK GREAT
function setInitPositions(dots)
{
    // INITIALIZE DOT POSITIONS TO BE ON TOP 
    // OF THE BULLETS IN THE <UL>
    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;
    }
    // PUT 0th DOT ABOVE 1ST (IT IS HIDDEN)
    dots[0].X = dots[1].X;
    dots[0].Y = dots[1].Y - SEGLEN;
}

// JUST SAVE MOUSE POSITION FOR Animate() TO USE
function MoveHandler(e)
{
    Xpos = e.pageX;
    Ypos = e.pageY;	  
    return true;
}

// JUST SAVE MOUSE POSITION FOR Animate() TO USE
function MoveHandlerIE() 
{
    Xpos = window.event.x + document.body.scrollLeft;
    Ypos = window.event.y + document.body.scrollTop;	  
}

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


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() 
{	
    // dots[0] FOLLOWS THE MOUSE,
    // THOUGH NO DOT IS DRAWN THERE
    var start = 0;

    if (followmouse == true) 
	{
        dots[0].X = Xpos;
        dots[0].Y = Ypos;	
        start = 1;
    }
	else
	{
		start = 0;
	}
    
    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);
        }
        
        // AIR RESISTANCE/FRICTION
        var resist = new vec(-dots[i].dx * RESISTANCE,
            -dots[i].dy * RESISTANCE);
        
        // COMPUTE NEW ACCEL, INCLUDING GRAVITY
        var accel = new vec((spring.X + resist.X)/ MASS,
            (spring.Y + resist.Y)/ MASS + GRAVITY);
        
        // COMPUTE NEW VELOCITY
        dots[i].dx += (DELTAT * accel.X);
        dots[i].dy += (DELTAT * accel.Y);
        
        // STOP DEAD SO IT DOESN'T JITTER WHEN NEARLY STILL
        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;
        }
        
        // MOVE TO NEW POSITION
        dots[i].X += dots[i].dx;
        dots[i].Y += dots[i].dy;
        
        // GET SIZE OF WINDOW
        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;
        }
        
        // BOUNCE OF 3 WALLS (LEAVE CEILING OPEN)
        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;
        }
        
        // MOVE IMG TO NEW POSITION
        dots[i].obj.left = dots[i].X;			
        dots[i].obj.top =  dots[i].Y;		
    }
}