var DDSPEED = 3;
var DDTIMER = 15;

// 处理鼠标动作的主函数 //
function ddMenu(id,d)
{
	var h = document.getElementById('ddheader' + id);
	var c = document.getElementById('ddcontent' + id);
	if (!c) return;
	clearInterval(c.timer);
	if(d == 1)
	{
		clearTimeout(h.timer);
		if(c.maxh && c.maxh <= c.offsetHeight) return;
		else if(!c.maxh)
		{
			c.style.display = 'block';
			c.style.height = 'auto';
			c.maxh = c.offsetHeight;
			c.style.height = '0px';
		}
		c.timer = setInterval(function(){ddSlide(c,1)},DDTIMER);
	}
	else
	{
		h.timer = setTimeout(function(){ddCollapse(c)},50);
	}
}

// 回缩菜单 //
function ddCollapse(c){
  c.timer = setInterval(function(){ddSlide(c,-1)},DDTIMER);
}

// 如果有用户将鼠标放置在菜单上则取消回缩 //
function cancelHide(id)
{
	var h = document.getElementById('ddheader' + id);
	var c = document.getElementById('ddcontent' + id);
	clearTimeout(h.timer);
	clearInterval(c.timer);
	if(c.offsetHeight < c.maxh)
	{
		c.timer = setInterval(function(){ddSlide(c,1)},DDTIMER);
	}
}

// 展开/回缩菜单，并设置透明度 //
function ddSlide(c,d)
{
	var currh = c.offsetHeight;
	var dist;
	if(d == 1)
	{
		dist = (Math.round((c.maxh - currh) / DDSPEED));
	}
	else
	{
		dist = (Math.round(currh / DDSPEED));
	}
	if(dist <= 1 && d == 1)
	{
		dist = 1;
	}
	c.style.height = currh + (dist * d) + 'px';
	c.style.opacity = currh / c.maxh;
	c.style.filter = 'alpha(opacity=' + (currh * 100 / c.maxh) + ')';
	if((currh < 2 && d != 1) || (currh > (c.maxh - 2) && d == 1))
	{
		clearInterval(c.timer);
	}
}