// The standard image of the page.
var standard_image_src="";

/* Preloads images such that there is no time delay when changing images.
 */
function on_load() {
  if ( document.getElementById('illustration') ) {
    var image1 = new Image();
    image1.src = 'images/nav_home.jpg';
    image1.src = 'images/nav_praxis.jpg';
    image1.src = 'images/nav_allgemeinmedizin.jpg';
    image1.src = 'images/nav_naturheilverfahren.jpg';
    image1.src = 'images/nav_lasertherapie.jpg';
    image1.src = 'images/nav_kontakt.jpg';
    image1.src = 'images/nav_impressum.jpg';
    image1.src = 'images/nav_links.jpg';
    if ( standard_image_src == "" ) {
      standard_image_src = document.getElementById('illustration').src;
    }
  }
}

/* Diplays the given image in the element with id 'illustration'.
*/
function display(new_illustration) {
  var illustration=document.getElementById('illustration');
  if ( illustration ) {
    if ( standard_image_src == "" ) {
      standard_image_src = illustration.src;
    }
    illustration.src="images/"+new_illustration;
  }
}

/* Displays the standard image of the page.
 */
function display_standard() {
  var illustration=document.getElementById('illustration');
  if ( illustration ) {
    if ( standard_image_src == "" ) {
      standard_image_src = illustration.src;
    }
    illustration.src = standard_image_src;
  }
}


var x_standard = 80;
var y_standard = 120;
var is_on_standard = true;

/* Butterfly changes its position.
 */
function chase_butterfly() {
  var butterfly = document.getElementById('Schmetterling');
  if ( is_on_standard ) {
    var dx=800;
    var dy=0;
    var xrand=Math.random()*dx;
    var yrand=Math.random()*dy;
    var left=parseInt(butterfly.style.left);
    var top=parseInt(butterfly.style.top);
    butterfly.style.left=String(left+xrand)+"px";
    butterfly.style.top=String(top+yrand)+"px";
    is_on_standard = false;
  } else {
    butterfly.style.left=String(x_standard)+"px";
    butterfly.style.top=String(y_standard)+"px";
    is_on_standard = true;
  }
}