iStartIndex = 0;

function swapImage(action) {
	
	var arrImages = new Array(	"anteprima-peschici-2.jpg", 
"anteprima-peschici-3.jpg", 
"anteprima-peschici-4.jpg", 
"anteprima-peschici-1.jpg", 
"anteprima-peschici-8.jpg", 
"anteprima-peschici-7.jpg", 
"anteprima-peschici-5.jpg", 
"anteprima-immagine-4.jpg", 
"anteprima-peschici-6.jpg", 
"anteprima-immagine-5.jpg", 
"anteprima-immagine-6.jpg", 
"anteprima-immagine2.jpg");

	
	
	imagePerBlock = 4; // mostra quattro immagini alla volta
	
		
	var iTotImages = arrImages.length;
		
	if (action == 'next') {
		iStartIndex = iStartIndex + imagePerBlock;
	}
	
	if (action == 'prev') {
		iStartIndex = iStartIndex - imagePerBlock;
	}

	
	// Visibilità tasti
	if (iStartIndex > (imagePerBlock - 1)) { // Nascondi tasto prev
		document.getElementById('divPrev').style.visibility = 'visible';
	} else {
		document.getElementById('divPrev').style.visibility = 'hidden';
	}
	
	
	if (iStartIndex >= (iTotImages - imagePerBlock)) { // Nascondi tasto next
		document.getElementById('divNext').style.visibility = 'hidden';
	} else {
		document.getElementById('divNext').style.visibility = 'visible';
	}
	

		
	// blocco immagini
	document.getElementById('img1').src = 'writable/tn_' + noImage(arrImages[iStartIndex], 'img1');
	document.getElementById('img2').src = 'writable/tn_' + noImage(arrImages[iStartIndex + 1], 'img2');
	document.getElementById('img3').src = 'writable/tn_' + noImage(arrImages[iStartIndex + 2], 'img3');
	document.getElementById('img4').src = 'writable/tn_' + noImage(arrImages[iStartIndex + 3], 'img4');
	
	// blocco link href
	document.getElementById('link1').href = 'writable/' + arrImages[iStartIndex];
	document.getElementById('link2').href = 'writable/' + arrImages[iStartIndex + 1];
	document.getElementById('link3').href = 'writable/' + arrImages[iStartIndex + 2];
	document.getElementById('link4').href = 'writable/' + arrImages[iStartIndex + 3];
	
	// blocco link title
	document.getElementById('link1').title = "";
	document.getElementById('link2').title = "";
	document.getElementById('link3').title = "";
	document.getElementById('link4').title = "";	
	

}


function noImage(arrValue, idImage) {
		
		if (arrValue == undefined) {
		
			document.getElementById(idImage).style.visibility = 'hidden';
		
		} else {
			
			document.getElementById(idImage).style.visibility = 'visible';
			return arrValue;
		}
	}

function galleryNext() {
	swapImage('next');
}

function galleryPrev() {
	swapImage('prev');
}