// resets currently highlighted image.
var currentImage = '';

// will be set to 'true' when all images are preloaded.
var preloadFlag = false;

// preload an image.
function newImage(arg) {
        if (document.images) {
                rslt = new Image();
                rslt.src = arg;
                return rslt;
        }
}

// change the currently highlighted image (e.g. changeCurrent('name1');).
function changeCurrent(arg) {
        currentImage = arg;
}

// exchange the source images of multiple image tags.
// (e.g. changeImages('name1', 'source1', 'name2', 'source2');)
function changeImages() {
        if (document.images && (preloadFlag == true)) {
                for (var i=0; i<changeImages.arguments.length; i+=2) {
                        if (changeImages.arguments[i] != currentImage) {
                                document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
                        }
                }
        }
}

// reset all image sources.
function resetImages() {
	changeCurrent('');
    changeImages(
			'btnHomepage',		'../softgames/gfx/de-nav-btn-homepage-n.gif',
			'btnPcgames',		'../softgames/gfx/de-nav-btn-pcgames-n.gif',
			'btnMobilegames',	'../softgames/gfx/de-nav-btn-mobilegames-n.gif',
			'btnContact',		'../softgames/gfx/de-nav-btn-contact-n.gif'
		);
}

// preload all images to be displayed.
function preloadImages() {
        if (document.images) {
                homepageN		= newImage('../softgames/gfx/de-nav-btn-homepage-n.gif');
                homepageO		= newImage('../softgames/gfx/de-nav-btn-homepage-o.gif');
                homepageP		= newImage('../softgames/gfx/de-nav-btn-homepage-p.gif');

                pcgamesN		= newImage('../softgames/gfx/de-nav-btn-pcgames-n.gif');
                pcgamesO		= newImage('../softgames/gfx/de-nav-btn-pcgames-o.gif');
                pcgamesP		= newImage('../softgames/gfx/de-nav-btn-pcgames-p.gif');

                mobilegamesN	= newImage('../softgames/gfx/de-nav-btn-mobilegames-n.gif');
                mobilegamesO	= newImage('../softgames/gfx/de-nav-btn-mobilegames-o.gif');
                mobilegamesP	= newImage('../softgames/gfx/de-nav-btn-mobilegames-p.gif');

                contactN		= newImage('../softgames/gfx/de-nav-btn-contact-n.gif');
                contactO		= newImage('../softgames/gfx/de-nav-btn-contact-o.gif');
                contactP		= newImage('../softgames/gfx/de-nav-btn-contact-p.gif');

                preloadFlag = true;
        }
}