function text_bottom(id)
{
 var height_txt = document.getElementById('txt_' + id).clientHeight;
 var height_canv = document.getElementById('canv_' + id).clientHeight;
 var y_old = parseInt(document.getElementById('txt_' + id).style.top);
 var y_new = y_old + height_canv - 10;
 //alert ('txt_'+id);
 if(y_old < 0)
 //alert ('height_txt - height_canv = '+(height_txt - height_canv)+', y_new = '+y_new)
 document.getElementById('txt_' + id).style.top = ((y_new < 0) ? y_new : 0) + 'px';
}
function text_top(id)
{
 var height_txt = document.getElementById('txt_' + id).clientHeight;
 var height_canv = document.getElementById('canv_' + id).clientHeight;
 var y_old = parseInt(document.getElementById('txt_' + id).style.top);
 var y_new = y_old - height_canv + 10;
 //alert ('txt_'+id);
 //alert (' '+y_old+' '+(height_txt - height_canv));
 if(y_old > -(height_txt - height_canv))
 document.getElementById('txt_' + id).style.top = ((-(height_txt - height_canv) < y_new) ? y_new : (-(height_txt - height_canv))) + 'px';
}