function slidetimer() {
 if (document.getElementById("slide1").style.display=="block") {
 document.getElementById("slide1").style.display = "none";
 document.getElementById("slide2").style.display = "block"; 
 document.getElementById("slide3").style.display = "none";
 document.getElementById("slide4").style.display = "none";
 
 document.getElementById("slide_tekst1").style.display = "none";
 document.getElementById("slide_tekst2").style.display = "block"; 
 document.getElementById("slide_tekst3").style.display = "none";
 document.getElementById("slide_tekst4").style.display = "none";
 
 document.getElementById("driehoek1").style.visibility = "hidden";
 document.getElementById("driehoek2").style.visibility = "visible"; 
 document.getElementById("driehoek3").style.visibility = "hidden";
 document.getElementById("driehoek4").style.visibility = "hidden";
 } else
 if (document.getElementById("slide2").style.display=="block") {
 document.getElementById("slide1").style.display = "none";
 document.getElementById("slide2").style.display = "none";
 document.getElementById("slide3").style.display = "block"; 
 document.getElementById("slide4").style.display = "none";
 
 document.getElementById("slide_tekst1").style.display = "none";
 document.getElementById("slide_tekst2").style.display = "none";
 document.getElementById("slide_tekst3").style.display = "block"; 
 document.getElementById("slide_tekst4").style.display = "none";
 
 document.getElementById("driehoek1").style.visibility = "hidden";
 document.getElementById("driehoek2").style.visibility = "hidden"; 
 document.getElementById("driehoek3").style.visibility = "visible";
 document.getElementById("driehoek4").style.visibility = "hidden";
 } else
 if (document.getElementById("slide3").style.display=="block") {
 document.getElementById("slide1").style.display = "none";
 document.getElementById("slide2").style.display = "none";
 document.getElementById("slide3").style.display = "none";
 document.getElementById("slide4").style.display = "block";
 
 document.getElementById("slide_tekst1").style.display = "none";
 document.getElementById("slide_tekst2").style.display = "none";
 document.getElementById("slide_tekst3").style.display = "none";
 document.getElementById("slide_tekst4").style.display = "block"; 
 
 document.getElementById("driehoek1").style.visibility = "hidden";
 document.getElementById("driehoek2").style.visibility = "hidden"; 
 document.getElementById("driehoek3").style.visibility = "hidden";
 document.getElementById("driehoek4").style.visibility = "visible"; 
 } else
 if (document.getElementById("slide4").style.display=="block") {
 document.getElementById("slide1").style.display = "block";    
 document.getElementById("slide2").style.display = "none";
 document.getElementById("slide3").style.display = "none";
 document.getElementById("slide4").style.display = "none";
 
 document.getElementById("slide_tekst1").style.display = "block";    
 document.getElementById("slide_tekst2").style.display = "none";
 document.getElementById("slide_tekst3").style.display = "none";
 document.getElementById("slide_tekst4").style.display = "none";
 
 document.getElementById("driehoek1").style.visibility = "visible";
 document.getElementById("driehoek2").style.visibility = "hidden"; 
 document.getElementById("driehoek3").style.visibility = "hidden";
 document.getElementById("driehoek4").style.visibility = "hidden";
 }      
}

function timeroff() {
 clearInterval(interval);
}

function timeron() {
 interval = setInterval('slidetimer()', 7000);
}

function show(showid) {
 if (showid == 1) {
 clearInterval(interval);
 document.getElementById("slide1").style.display = "block";
 document.getElementById("slide2").style.display = "none";
 document.getElementById("slide3").style.display = "none";
 document.getElementById("slide4").style.display = "none";
 
 document.getElementById("slide_tekst1").style.display = "block";
 document.getElementById("slide_tekst2").style.display = "none";
 document.getElementById("slide_tekst3").style.display = "none";
 document.getElementById("slide_tekst4").style.display = "none"; 
 
 document.getElementById("driehoek1").style.visibility = "visible";
 document.getElementById("driehoek2").style.visibility = "hidden"; 
 document.getElementById("driehoek3").style.visibility = "hidden";
 document.getElementById("driehoek4").style.visibility = "hidden";
}
 if (showid == 2) {
 clearInterval(interval);
 document.getElementById("slide1").style.display = "none";
 document.getElementById("slide2").style.display = "block";
 document.getElementById("slide3").style.display = "none";
 document.getElementById("slide4").style.display = "none";
 
 document.getElementById("slide_tekst1").style.display = "none";
 document.getElementById("slide_tekst2").style.display = "block";
 document.getElementById("slide_tekst3").style.display = "none";
 document.getElementById("slide_tekst4").style.display = "none"; 
 
 document.getElementById("driehoek1").style.visibility = "hidden";
 document.getElementById("driehoek2").style.visibility = "visible"; 
 document.getElementById("driehoek3").style.visibility = "hidden";
 document.getElementById("driehoek4").style.visibility = "hidden";
}
 if (showid == 3) {
 clearInterval(interval);
 document.getElementById("slide1").style.display = "none";
 document.getElementById("slide2").style.display = "none";
 document.getElementById("slide3").style.display = "block";
 document.getElementById("slide4").style.display = "none";
 
 document.getElementById("slide_tekst1").style.display = "none";
 document.getElementById("slide_tekst2").style.display = "none";
 document.getElementById("slide_tekst3").style.display = "block";
 document.getElementById("slide_tekst4").style.display = "none"; 
 
 document.getElementById("driehoek1").style.visibility = "hidden";
 document.getElementById("driehoek2").style.visibility = "hidden"; 
 document.getElementById("driehoek3").style.visibility = "visible";
 document.getElementById("driehoek4").style.visibility = "hidden"; 
}
 if (showid == 4) {
 clearInterval(interval);
 document.getElementById("slide1").style.display = "none";
 document.getElementById("slide2").style.display = "none";
 document.getElementById("slide3").style.display = "none";
 document.getElementById("slide4").style.display = "block";
 
 document.getElementById("slide_tekst1").style.display = "none";
 document.getElementById("slide_tekst2").style.display = "none";
 document.getElementById("slide_tekst3").style.display = "none";
 document.getElementById("slide_tekst4").style.display = "block"; 
 
 document.getElementById("driehoek1").style.visibility = "hidden";
 document.getElementById("driehoek2").style.visibility = "hidden"; 
 document.getElementById("driehoek3").style.visibility = "hidden";
 document.getElementById("driehoek4").style.visibility = "visible";
}                
}

function start_slider() {
 interval = setInterval('slidetimer()', 7000);
 show(1);
 timeron();
}