function project_next(stripnr) {
  project_page[stripnr]++;
  project_render(stripnr);
}

function project_prev(stripnr) {
  project_page[stripnr]--;
  project_render(stripnr);
}

function project_render(stripnr) {
  var display = '';
  for(var i=1; i<=project_count[stripnr]; i++) {
    if (i>=(project_page[stripnr]-1)*4+1 && i<=(project_page[stripnr]*4))
      display = 'inline';
    else
      display = 'none';
    document.getElementById('project_'+stripnr+'_'+i).style.display = display;
  }
  
  if (project_page[stripnr] > 1)
    set_project_prev(true, stripnr);
  else
    set_project_prev(false,stripnr);
  if ((project_page[stripnr])*4+1 <= project_count[stripnr])
    set_project_next(true, stripnr);
  else
    set_project_next(false, stripnr);  
}

function set_project_prev(tf, stripnr) {
  var display = '';
  if (tf) display = 'inline';
  else display = 'none';
  document.getElementById('project_prev'+stripnr).style.display = display;
}
function set_project_next(tf, stripnr) {
  var display = '';
  if (tf) display = 'inline';
  else display = 'none';
  document.getElementById('project_next'+stripnr).style.display = display;
}