function OpacityControl( overlay ) {
	this.overlay = overlay;
}

OpacityControl.prototype = new GControl();

//This function positions the slider to match the specified opacity
OpacityControl.prototype.setSlider = function(pos) {
	var left = Math.round((58*pos));
	this.slide.left = left;
	this.knob.style.left = left+"px";
	this.knob.style.top = "0px";
}

//This function reads the slider and sets the overlay opacity level
OpacityControl.prototype.setOpacity = function() {
	this.overlay.getTileLayer().opacity = this.slide.left/58;
	this.map.removeOverlay(this.overlay);
	this.map.addOverlay(this.overlay);
}

//This is called by the API when addControl(new OpacityControl())
OpacityControl.prototype.initialize = function(map) {
	var that=this;
	this.map = map;

	//If MSIE, need to use AlphaImageLoader
		var agent = navigator.userAgent.toLowerCase();
		if ((agent.indexOf("msie") > -1) && (agent.indexOf("opera") < 1)){this.ie = true} else {this.ie = false}

	//Create the background graphic as a <div> containing an image
		var container = document.createElement("div");
		container.style.width="70px";
		container.style.height="21px";

	//Handle transparent PNG files in MSIE
		if (this.ie) {
		var loader = "filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='images/opacity_slider.png', sizingMethod='crop');";
			container.innerHTML = '<div style="height:31px; width:70px; background-color:#666666; ' +loader+ '" ></div>';
		} else {
		container.innerHTML = '<div style="height:31px; width:70px; background-color:#666666; background-image: url(images/opacity_slider.png)" ></div>';
		}

	//Create the knob as a GDraggableObject
	//Handle transparent PNG files in MSIE
		if (this.ie) {
		var loader = "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='images/opacity_slider.png', sizingMethod='crop');";
		this.knob = document.createElement("div");
		this.knob.style.height="21px";
		this.knob.style.width="13px";
		this.knob.style.overflow="hidden";
		this.knob_img = document.createElement("div");
		this.knob_img.style.height="21px";
		this.knob_img.style.width="83px";
		this.knob_img.style.filter=loader;
		this.knob_img.style.position="relative";
		this.knob_img.style.left="-70px";
		this.knob.appendChild(this.knob_img);
		} else {
		this.knob = document.createElement("div");
		this.knob.style.height="21px";
		this.knob.style.width="13px";
		this.knob.style.backgroundImage="url(images/opacity_slider.png)";
		this.knob.style.backgroundPosition="-70px 0px";
		}
		container.appendChild(this.knob);
		this.slide=new GDraggableObject(this.knob, {container:container});
		this.slide.setDraggableCursor('pointer');
		this.slide.setDraggingCursor('pointer');
		this.container = container;

	//Attach the control to the map
	map.getContainer().appendChild(container);

	//Init slider
	this.setSlider(this.overlay.getTileLayer().opacity );

	//Listen for the slider being moved and set the opacity
	GEvent.addListener(this.slide, "dragend", function() {that.setOpacity()});
	//GEvent.addListener(this.container, "click", function( x, y ) { alert(x, y) });

return container;
}

//Set the default position for the control
OpacityControl.prototype.getDefaultPosition = function() {
return new GControlPosition(G_ANCHOR_TOP_RIGHT, new GSize(7, 47));
}