var SPEED = 0.01;
var TIMER =30;

function make_transparent(element)
{
	var id = element.id;	//bl_x_y
	decrease_opacity(id, 0);
}

function make_darked(element)
{
	var id = element.id;	//bl_x_y
	increase_opacity(id, 0.2);
}


function decrease_opacity(id, target_opacity)
{
	element = document.getElementById(id);
	if (element)
	{
		clearInterval(element.timer);
		element.timer = setInterval("shrink_opacity('"+id+"',"+target_opacity+")", TIMER);
	}
}
function increase_opacity(id, target_opacity)
{
	element = document.getElementById(id);
	if (element)
	{
		clearInterval(element.timer);
		//element.style.opacity = 0.15;
		element.timer = setInterval("grow_opacity('"+id+"',"+target_opacity+")", TIMER);
	}
}

function grow_opacity(id,target_opacity)
{
	try
	{
		element = document.getElementById(id);
		if (element.style.opacity < target_opacity)	
			element.style.opacity = element.style.opacity - (-SPEED);
		else
			clearInterval(element.timer);
	}
	catch (e) {}
}
function shrink_opacity(id,target_opacity)
{
	try
	{
		element = document.getElementById(id);
		if (element.style.opacity > target_opacity)	
			element.style.opacity = element.style.opacity - SPEED;
		else
		{
			clearInterval(element.timer);
		}
	}
	catch (e) {}
}