function get_prefix(filename) {
    var posit=filename.lastIndexOf("_");
    var prefix=filename.substr(0, posit);
    return prefix;
}

function get_extension(filename) {
    var posit=filename.lastIndexOf(".");
    var ext=filename.substr(posit+1);
    return ext;
}

function get_filename(full_path) {
    var posit=full_path.lastIndexOf("/");
    var file=full_path.substr(posit+1);
    return file;
}

function option_over(id_image) {
    var imgOption=document.getElementById(id_image);
    var prefix=get_prefix(imgOption.src);
    var ext=get_extension(imgOption.src);
    imgOption.src=prefix+'_over'+'.'+ext;
}

function option_on(id_image) {
    var imgOption=document.getElementById(id_image);
    var prefix=get_prefix(imgOption.src);
    var ext=get_extension(imgOption.src);
    imgOption.src=prefix+'_on'+'.'+ext;
}

function swap_menu(id_image, id_menu) {
    var menu=document.getElementById(id_menu);
    var imgOption=document.getElementById(id_image);
    if(menu.style.display=='none') {
        menu.style.display='block';
        option_over(id_image);
        imgOption.onmouseover='';
        imgOption.onmouseout=''; 
    } else {
        menu.style.display='none';
        option_on(id_image);
        imgOption.onmouseover=function over(e) { option_over(id_image); };
        imgOption.onmouseout=function out(e) { option_on(id_image); }; 
    }
}

function swap_option(id_image) {
    var imgOption=document.getElementById(id_image);
    var prefix=get_prefix(imgOption.src);
    var ext=get_extension(imgOption.src);
    if(imgOption.src==prefix+'_on'+'.'+ext) {
        imgOption.src=prefix+'_over'+'.'+ext;
    } else {
        imgOption.src=prefix+'_on'+'.'+ext;
    }
}