//position values of a mouse event
//usage:   var pos = new MousePosition(mouse_event);
function MousePosition(evt)
{
	this.screen = {
		x: evt.screenX,
		y: evt.screenY
	};
	this.window = this.frame = {
		x: evt.clientX,
		y: evt.clientY
	};
 
	if(isNaN(evt.pageX) || isNaN(evt.pageY))
	{
		//scroll position of document
		var left, top;
		if(window.pageYOffset)	//all except IE
		{
			left = window.pageXOffset;
			top = window.pageYOffset;
		}
		else if(document.documentElement && !isNaN(document.documentElement.scrollTop))	//IE standards compliance mode
		{
			left = document.documentElement.scrollLeft;
			top = document.documentElement.scrollTop;
		}
		else	//IE quirks mode
		{
			left = document.body.scrollLeft;
			top = document.body.scrollTop;
		}
 
		this.document = {
			x: left + evt.clientX,
			y: top + evt.clientY
		};
	}
	else
	{
		this.document = {
			x: evt.pageX,
			y: evt.pageY
		};
	}
 
	this.layer = {
		x: evt.layerX || evt.x,
		y: evt.layerY || evt.y
	};
}
 
//returns event.button in both the W3C and Microsoft models
//in IE lte 8, a button combination (like 3==left+right) returns -1 for the W3C model
function mouseButton(evt)
{
	var ms, w3c;
 
	//in the W3C model, 0==left, 1==middle, 2==right
	//in the Microsoft model, 1==left, 4==middle, 2==right
 
	if(evt.which)
	{
		w3c = evt.which - 1;
		ms = evt.which == 1 ? 1 /*left*/ : evt.which == 2 ? 4 /*middle*/ : 2 /*right*/;
	}
	else	//IE lte 8
	{
		ms = evt.button;	//actually, this would need to be: evt.button & !previous_evt_button
							//otherwise, if evt.button == 3 (for example), it could be either the left or the right button
							//since we can't reliably keep track of the previous evt.button, we will use -1 for the w3c value
							// if ms is not 1, 4, or 2
		w3c = ms == 1 ? 0 /*left*/ : ms == 4 ? 1 /*middle*/ : ms == 2 ? 2 /*right*/ : -1 /*unknown*/;
	}
 
	return {w3c: w3c, ms: ms};
};