function show_layer(name)
{
  var calque = document.getElementById(name);

  calque.style.display = "block";
}

function hide_layer(name)
{
  var calque = document.getElementById(name);

  calque.style.display = "none";
}

function rollover(name)
{
  var obj = document.getElementById(name);
  var nom;
  
  if (obj != null)
  {
    nom = obj.src.substring(0, obj.src.lastIndexOf('.') - 3);
    nom += "on.png";
    obj.src = nom;
  }
}

function rollout(name)
{
  var obj = document.getElementById(name);
  var nom;
  
  if (obj != null)
  {
    nom = obj.src.substring(0, obj.src.lastIndexOf('.') - 2);
    nom += "off.png";
    obj.src = nom;
  }
}