function opacity()
{
    this.opacity_1 = 100;
    this.opacity_2 = 100;
    this.opacity_3 = 100;
    this.opacity_4 = 100;
}

function obrazek(_id)
{
    this.on = setTimeout('',99999);
    this.off = setTimeout('',99999);
    this.img1 = document.getElementById('bg_1').style; 
    this.img2 = document.getElementById('bg_2').style; 
    this.img3 = document.getElementById('bg_3').style;  
    this.img4 = document.getElementById('bg_4').style;  
}

var oImages = new obrazek();
var oOpacity = new opacity();

function zmien_tlo(nr, flaga)
{
    aDiv = new Array();
    
    aDiv[1] = oImages.img1;
    aDiv[2] = oImages.img2;
    aDiv[3] = oImages.img3;
    aDiv[4] = oImages.img4;
    
    if (flaga == 'on')
    {
        clearTimeout(oImages.off);
    
        if (nr == 1)
        {
        if (oOpacity.opacity_1 >= 100 && oOpacity.opacity_2 <= 30 && oOpacity.opacity_3 <= 30 && oOpacity.opacity_4 <= 30)
            {
            clearTimeout(oImages.on);
            return (false);
            }
        if (oOpacity.opacity_1 < 100)
            oOpacity.opacity_1 = oOpacity.opacity_1 + 2;
        if (oOpacity.opacity_2 > 30)
            oOpacity.opacity_2 = oOpacity.opacity_2 - 2;
        if (oOpacity.opacity_3 > 30)
            oOpacity.opacity_3 = oOpacity.opacity_3 - 2;  
        if (oOpacity.opacity_4 > 30)
            oOpacity.opacity_4 = oOpacity.opacity_4 - 2;  
        }
        else if (nr == 2)
        {
        if (oOpacity.opacity_2 >= 100 && oOpacity.opacity_1 <= 30 && oOpacity.opacity_3 <= 30 && oOpacity.opacity_4 <= 30)
            {
            clearTimeout(oImages.on);
            return (false);
            }
        if (oOpacity.opacity_2 < 100)
            oOpacity.opacity_2 = oOpacity.opacity_2 + 2;
        if (oOpacity.opacity_1 > 30)
            oOpacity.opacity_1 = oOpacity.opacity_1 - 2;
        if (oOpacity.opacity_3 > 30)
            oOpacity.opacity_3 = oOpacity.opacity_3 - 2; 
        if (oOpacity.opacity_4 > 30)
            oOpacity.opacity_4 = oOpacity.opacity_4 - 2;       
        }
        else if (nr == 3)
        {
        if (oOpacity.opacity_3 >= 100 && oOpacity.opacity_2 <= 30 && oOpacity.opacity_1 <= 30 && oOpacity.opacity_4 <= 30)
            {
            clearTimeout(oImages.on);
            return (false);
            }
        if (oOpacity.opacity_3 < 100)
            oOpacity.opacity_3 = oOpacity.opacity_3 + 2;
        if (oOpacity.opacity_2 > 30)
            oOpacity.opacity_2 = oOpacity.opacity_2 - 2;
        if (oOpacity.opacity_1 > 30)
            oOpacity.opacity_1 = oOpacity.opacity_1 - 2;      
        if (oOpacity.opacity_4 > 30)
            oOpacity.opacity_4 = oOpacity.opacity_4 - 2;    
        }
        else if (nr == 4)
        {
        if (oOpacity.opacity_4 >= 100 && oOpacity.opacity_2 <= 30 && oOpacity.opacity_1 <= 30 && oOpacity.opacity_3 <= 30)
            {
            clearTimeout(oImages.on);
            return (false);
            }
        if (oOpacity.opacity_4 < 100)
            oOpacity.opacity_4 = oOpacity.opacity_4 + 2;
        if (oOpacity.opacity_2 > 30)
            oOpacity.opacity_2 = oOpacity.opacity_2 - 2;
        if (oOpacity.opacity_1 > 30)
            oOpacity.opacity_1 = oOpacity.opacity_1 - 2;      
        if (oOpacity.opacity_3 > 30)
            oOpacity.opacity_3 = oOpacity.opacity_3 - 2;    
        }
        
        for (var i = 1 ; i<5 ; i++)
        {
                if (i == 1)
                {
                    aDiv[i].opacity = (oOpacity.opacity_1 / 100);
                    aDiv[i].MozOpacity = (oOpacity.opacity_1 / 100);
                    aDiv[i].KhtmlOpacity = (oOpacity.opacity_1 / 100);
                    aDiv[i].filter = "alpha(opacity=" + oOpacity.opacity_1 + ")";        
                }
                else if (i == 2)
                {
                    aDiv[i].opacity = (oOpacity.opacity_2 / 100);
                    aDiv[i].MozOpacity = (oOpacity.opacity_2 / 100);
                    aDiv[i].KhtmlOpacity = (oOpacity.opacity_2 / 100);
                    aDiv[i].filter = "alpha(opacity=" + oOpacity.opacity_2 + ")";        
                }
                else if (i == 3)
                {
                    aDiv[i].opacity = (oOpacity.opacity_3 / 100);
                    aDiv[i].MozOpacity = (oOpacity.opacity_3 / 100);
                    aDiv[i].KhtmlOpacity = (oOpacity.opacity_3 / 100);
                    aDiv[i].filter = "alpha(opacity=" + oOpacity.opacity_3 + ")";        
                }
                else if (i == 4)
                {
                    aDiv[i].opacity = (oOpacity.opacity_4 / 100);
                    aDiv[i].MozOpacity = (oOpacity.opacity_4 / 100);
                    aDiv[i].KhtmlOpacity = (oOpacity.opacity_4 / 100);
                    aDiv[i].filter = "alpha(opacity=" + oOpacity.opacity_4 + ")";        
                }
        }

    oImages.on = setTimeout("zmien_tlo('"+nr+"', '"+flaga+"', ' ')",1); 
    } 
    else if (flaga == 'off')
    {
        clearTimeout(oImages.on);
    
        if (oOpacity.opacity_1 >= 100 && oOpacity.opacity_2 >= 100 && oOpacity.opacity_3 >= 100 && oOpacity.opacity_4 >= 100)
            {
            clearTimeout(oImages.off);
            return (false);
            }
        if (oOpacity.opacity_1 < 100)
            oOpacity.opacity_1 = oOpacity.opacity_1 + 2;
        if (oOpacity.opacity_2 < 100)
            oOpacity.opacity_2 = oOpacity.opacity_2 + 2;
        if (oOpacity.opacity_3 < 100)
            oOpacity.opacity_3 = oOpacity.opacity_3 + 2;
        if (oOpacity.opacity_4 < 100)
            oOpacity.opacity_4 = oOpacity.opacity_4 + 2;

        
        for (var i = 1 ; i<5 ; i++)
        {
                if (i == 1)
                {
                    aDiv[i].opacity = (oOpacity.opacity_1 / 100);
                    aDiv[i].MozOpacity = (oOpacity.opacity_1 / 100);
                    aDiv[i].KhtmlOpacity = (oOpacity.opacity_1 / 100);
                    aDiv[i].filter = "alpha(opacity=" + oOpacity.opacity_1 + ")";        
                }
                else if (i == 2)
                {
                    aDiv[i].opacity = (oOpacity.opacity_2 / 100);
                    aDiv[i].MozOpacity = (oOpacity.opacity_2 / 100);
                    aDiv[i].KhtmlOpacity = (oOpacity.opacity_2 / 100);
                    aDiv[i].filter = "alpha(opacity=" + oOpacity.opacity_2 + ")";        
                }
                else if (i == 3)
                {
                    aDiv[i].opacity = (oOpacity.opacity_3 / 100);
                    aDiv[i].MozOpacity = (oOpacity.opacity_3 / 100);
                    aDiv[i].KhtmlOpacity = (oOpacity.opacity_3 / 100);
                    aDiv[i].filter = "alpha(opacity=" + oOpacity.opacity_3 + ")";        
                }
                else if (i == 4)
                {
                    aDiv[i].opacity = (oOpacity.opacity_4 / 100);
                    aDiv[i].MozOpacity = (oOpacity.opacity_4 / 100);
                    aDiv[i].KhtmlOpacity = (oOpacity.opacity_4 / 100);
                    aDiv[i].filter = "alpha(opacity=" + oOpacity.opacity_4 + ")";        
                }
        }

    oImages.off = setTimeout("zmien_tlo('"+nr+"', '"+flaga+"', ' ')",1); 
    }  
}