element that contains all of the
elements to be shown as a slide show.
buttonID: "slideShowButton", // The ID of the
element that toggles the slide show on and off.
buttonStartText: "Start Slides", // Text used in the slide show toggle button.
buttonStopText: "Stop Slides", // Text used in the slide show toggle button.
wrapperObject: null, // Will contain a reference to the element that contains all of the
elements to be shown as a slide show.
buttonObject: null, // If present, will contain a reference to the
element that toggles the slide show on and off. The initial assumption is that there is no such button element (hence the false value).
slideImages: [], // Will contain all of the slide image objects.
slideShowID: null, // A setInterval() ID value used to stop the slide show.
slideShowRunning: true, // Used to record when the slide show is running and when it's not. The slide show is always initially running.
slideIndex: 0 // The index of the current slide image.
}
/* MAIN *************************************************************************************************/
initializeGlobals();
if ( insufficientSlideShowMarkup() ) {
return; // Insufficient slide show markup - exit now.
}
// Assert: there's at least one slide image.
if (globals.slideImages.length == 1) {
return; // The solo slide image is already being displayed - exit now.
}
// Assert: there's at least two slide images.
initializeSlideShowMarkup();
globals.wrapperObject.addEventListener('click', toggleSlideShow, false); // If the user clicks a slide show image, it toggles the slide show on and off.
if (globals.buttonObject) {
globals.buttonObject.addEventListener('click', toggleSlideShow, false); // This callback is used to toggle the slide show on and off.
}
startSlideShow();
/* FUNCTIONS ********************************************************************************************/
function initializeGlobals() {
globals.wrapperObject = (document.getElementById(globals.wrapperID) ? document.getElementById(globals.wrapperID) : null);
globals.buttonObject = (document.getElementById(globals.buttonID) ? document.getElementById(globals.buttonID) : null);
if (globals.wrapperObject) {
globals.slideImages = (globals.wrapperObject.querySelectorAll('img') ? globals.wrapperObject.querySelectorAll('img') : []);
}
} // initializeGlobals
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
function insufficientSlideShowMarkup() {
if (!globals.wrapperObject) { // There is no wrapper element whose ID is globals.wrapperID - fatal error.
if (globals.buttonObject) {
globals.buttonObject.style.display = "none"; // Hide the not needed slide show button element when present.
}
return true;
}
if (!globals.slideImages.length) { // There needs to be at least one slide wrapper element.
}
if (globals.buttonObject) {
globals.buttonObject.style.display = "none"; // Hide the not needed slide show button element.
}
return true;
}
return false; // The markup expected by this library seems to be present.
} // insufficientSlideShowMarkup
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
function initializeSlideShowMarkup() {
var slideWidthMax = maxSlideWidth(); // Returns a value that is always in pixel units.
var slideHeightMax = maxSlideHeight(); // Returns a value that is always in pixel units.
globals.wrapperObject.style.position = "relative";
globals.wrapperObject.style.overflow = "hidden"; // This is just a safety thing.
globals.wrapperObject.style.width = slideWidthMax + "px";
globals.wrapperObject.style.height = slideHeightMax + "px";
var slideCount = globals.slideImages.length;
for (var i = 0; i < slideCount; i++) {
globals.slideImages[i].style.opacity = 0;
globals.slideImages[i].style.position = "absolute";
globals.slideImages[i].style.top = (slideHeightMax - globals.slideImages[i].getBoundingClientRect().height) / 2 + "px";
globals.slideImages[i].style.left = (slideWidthMax - globals.slideImages[i].getBoundingClientRect().width) / 2 + "px";
}
globals.slideImages[0].style.opacity = 1; // Make the first slide visible.
if (globals.buttonObject) {
globals.buttonObject.textContent = globals.buttonStopText;
}
} // initializeSlideShowMarkup
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
function maxSlideWidth() {
var maxWidth = 0;
var maxSlideIndex = 0;
var slideCount = globals.slideImages.length;
for (var i = 0; i < slideCount; i++) {
if (globals.slideImages[i].width > maxWidth) {
maxWidth = globals.slideImages[i].width; // The width of the widest slide so far.
maxSlideIndex = i; // The slide with the widest width so far.
}
}
return globals.slideImages[maxSlideIndex].getBoundingClientRect().width; // Account for the image's border, padding, and margin values. Note that getBoundingClientRect() is always in units of pixels.
} // maxSlideWidth
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
function maxSlideHeight() {
var maxHeight = 0;
var maxSlideIndex = 0;
var slideCount = globals.slideImages.length;
for (var i = 0; i < slideCount; i++) {
if (globals.slideImages[i].height > maxHeight) {
maxHeight = globals.slideImages[i].height; // The height of the tallest slide so far.
maxSlideIndex = i; // The slide with the tallest height so far.
}
}
return globals.slideImages[maxSlideIndex].getBoundingClientRect().height; // Account for the image's border, padding, and margin values. Note that getBoundingClientRect() is always in units of pixels.
} // maxSlideHeight
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
function startSlideShow() {
globals.slideShowID = setInterval(transitionSlides, globals.slideDelay);
} // startSlideShow
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
function haltSlideShow() {
clearInterval(globals.slideShowID);
} // haltSlideShow
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
function toggleSlideShow() {
if (globals.slideShowRunning) {
haltSlideShow();
if (globals.buttonObject) {
globals.buttonObject.textContent = globals.buttonStartText;
}
}
else {
startSlideShow();
if (globals.buttonObject) {
globals.buttonObject.textContent = globals.buttonStopText;
}
}
globals.slideShowRunning = !(globals.slideShowRunning);
} // toggleSlideShow
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
function transitionSlides() {
var currentSlide = globals.slideImages[globals.slideIndex];
++(globals.slideIndex);
if (globals.slideIndex >= globals.slideImages.length) {
globals.slideIndex = 0;
}
var nextSlide = globals.slideImages[globals.slideIndex];
var currentSlideOpacity = 1; // Fade the current slide out.
var nextSlideOpacity = 0; // Fade the next slide in.
var opacityLevelIncrement = 1 / globals.fadeDelay;
var fadeActiveSlidesID = setInterval(fadeActiveSlides, globals.fadeDelay);
function fadeActiveSlides() {
currentSlideOpacity -= opacityLevelIncrement;
nextSlideOpacity += opacityLevelIncrement;
// console.log(currentSlideOpacity + nextSlideOpacity); // This should always be very close to 1.
if (currentSlideOpacity >= 0 && nextSlideOpacity <= 1) {
currentSlide.style.opacity = currentSlideOpacity;
nextSlide.style.opacity = nextSlideOpacity;
}
else {
currentSlide.style.opacity = 0;
nextSlide.style.opacity = 1;
clearInterval(fadeActiveSlidesID);
}
} // fadeActiveSlides
} // transitionSlides
} // slideShow