$(document).ready(function(){
    var i1, i2, $v = $('#viewport'), l = document.getElementById('left'), r = document.getElementById('right');
    
    var doButtons = function(){
        var inn = [], out = [], sl = $v.scrollLeft();
        if(sl > 0) { inn.push(l); } else { out.push(l); }
        if(sl < $('ul.columnSet', $v).width() - 890) { inn.push(r); } else { out.push(r); }
            
        $(inn).fadeIn(300);
        $(out).fadeOut(300);
    }
    
    $('#viewport-wrapper').hover(doButtons, function(){ 
        $('#left, #right').fadeOut(300); 
    });
    
    $('#left').mousedown(function(){
        var go = function() { $v.scrollTo('-=40'); }
        go();
        i2 = setInterval(go, 100);
    }).mouseup(function(){ clearInterval(i2); doButtons(); });
    
    $('#right').mousedown(function(){
        var go = function() { $v.scrollTo('+=40'); }
        go();
        i2 = setInterval(go, 100);
    }).mouseup(function(){ clearInterval(i2); doButtons(); });
});