ele_on = null;

function opacity(id, opacStart, opacEnd, millisec) {
     var speed = Math.round(millisec / 100);
    var timer = 0;

    if(opacStart > opacEnd) {
        for(i = opacStart; i >= opacEnd; i--) {
            setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed));
            timer++;
        }
    } else if(opacStart < opacEnd) {
        for(i = opacStart; i <= opacEnd; i++)
            {
            setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed));
            timer++;
        }
    }
}

function m1_on(){
    if(ele_on == 'm1'){
        location.href = 'Nav.aspx?pageid=3';
    }else{
        ele_on = 'm1';
        changeOpac(0, 'm1');
        document.getElementById('m2').style.display = 'none';
        document.getElementById('m3').style.display = 'none';
        document.getElementById('m4').style.display = 'none';
        document.getElementById('m1').style.display = 'block';
        opacity('m1', 0,100,500);
    }
}

function m1_off(){
    ele_on = null;
    opacity('m1', 100,0,500);
}

function m2_on(){
    if(ele_on == 'm2'){
        location.href = 'Nav.aspx?pageid=6';
    }else{
        ele_on = 'm2';
        changeOpac(0, 'm2');
        document.getElementById('m1').style.display = 'none';
        document.getElementById('m3').style.display = 'none';
        document.getElementById('m4').style.display = 'none';
        document.getElementById('m2').style.display = 'block';
        opacity('m2', 0,100,500);
    }
}

function m2_off(){
    ele_on = null;
    opacity('m2', 100,0,500);
}

function m3_on(){
    if(ele_on == 'm3'){
        location.href = 'Nav.aspx?pageid=7';
    }else{
        ele_on = 'm3';
        changeOpac(0, 'm3');
        document.getElementById('m1').style.display = 'none';
        document.getElementById('m2').style.display = 'none';
        document.getElementById('m4').style.display = 'none';
        document.getElementById('m3').style.display = 'block';
        opacity('m3', 0,100,500);
    }
}

function m3_off(){
    ele_on = null;
    opacity('m3', 100,0,500);
}


function m4_on(){
    if(ele_on == 'm4'){
        location.href = 'Nav.aspx?pageid=8';
    }else{
        ele_on = 'm4';
        changeOpac(0, 'm4');
        document.getElementById('m1').style.display = 'none';
        document.getElementById('m2').style.display = 'none';
        document.getElementById('m3').style.display = 'none';
        document.getElementById('m4').style.display = 'block';
        opacity('m4', 0,100,500);
    }
}

function m4_off(){
    ele_on = null;
    opacity('m4', 100,0,500);
}

function changeOpac(opacity, id) {
    var object = document.getElementById(id).style;
    object.opacity = (opacity / 100);
    object.MozOpacity = (opacity / 100);
    object.KhtmlOpacity = (opacity / 100);
    object.filter = "alpha(opacity=" + opacity + ")";
}