var maxImages=0;
var imageHeight=0;
var maxFrameHeight=0;
var galleryFrameId;

function galleryInit(id,scrollHeight,maxImagesVisible){
    galleryFrame = document.getElementById(id);
    imageItems = galleryFrame.getElementsByTagName('img');
    
    maxImages=imageItems.length;
    imageHeight=scrollHeight;
    maxFrameHeight=imageHeight*(maxImages-maxImagesVisible);
    galleryFrameId=id;
    
    document.getElementById(galleryFrameId).style.position='relative';
    document.getElementById(galleryFrameId).style.top='0px';
}

function galleryScrollUp(){
    var sPos=document.getElementById(galleryFrameId).style.top;
    sPos=sPos.replace('px', '');
    
    var iPos=parseInt(sPos)
    if(iPos<0){
        iPos+=imageHeight;
        document.getElementById(galleryFrameId).style.top=iPos+'px';
    }
}

function galleryScrollDown(){
    var sPos=document.getElementById(galleryFrameId).style.top;
    sPos=sPos.replace('px', '');
    
    var iPos=parseInt(sPos)
    if(iPos>-maxFrameHeight){
        iPos-=imageHeight;
        document.getElementById(galleryFrameId).style.top=iPos+'px';
    }
}