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From 2014.igem.org

$(window).load(function(){

// We are listening to the window.load event, so we can be sure // that the images in the slideshow are loaded properly.

// Testing wether the current browser supports the canvas element: var supportCanvas = 'getContext' in document.createElement('canvas');

// The canvas manipulations of the images are CPU intensive, // this is why we are using setTimeout to make them asynchronous // and improve the responsiveness of the page.

var slides = $('#slideshow li'), current = 0, slideshow = {width:0,height:0};

setTimeout(function(){

window.console && window.console.time && console.time('Generated In');

if(supportCanvas){ $('#slideshow img').each(function(){

if(!slideshow.width){ // Taking the dimensions of the first image: slideshow.width = this.width; slideshow.height = this.height; }

// Rendering the modified versions of the images: createCanvasOverlay(this); }); }

window.console && window.console.timeEnd && console.timeEnd('Generated In');

$('#slideshow .arrow').click(function(){ var li = slides.eq(current), canvas = li.find('canvas'), nextIndex = 0;

// Depending on whether this is the next or previous // arrow, calculate the index of the next slide accordingly.

if($(this).hasClass('next')){ nextIndex = current >= slides.length-1 ? 0 : current+1; } else { nextIndex = current <= 0 ? slides.length-1 : current-1; }

var next = slides.eq(nextIndex);

if(supportCanvas){

// This browser supports canvas, fade it into view:

canvas.fadeIn(function(){

// Show the next slide below the current one: next.show(); current = nextIndex;

// Fade the current slide out of view: li.fadeOut(function(){ li.removeClass('slideActive'); canvas.hide(); next.addClass('slideActive'); }); }); } else {

// This browser does not support canvas. // Use the plain version of the slideshow.

current=nextIndex; next.addClass('slideActive').show(); li.removeClass('slideActive').hide(); } });

},100);

// This function takes an image and renders // a version of it similar to the Overlay blending // mode in Photoshop.

function createCanvasOverlay(image){

var canvas = document.createElement('canvas'), canvasContext = canvas.getContext("2d");

// Make it the same size as the image canvas.width = slideshow.width; canvas.height = slideshow.height;

// Drawing the default version of the image on the canvas: canvasContext.drawImage(image,0,0);

// Taking the image data and storing it in the imageData array: var imageData = canvasContext.getImageData(0,0,canvas.width,canvas.height), data = imageData.data;

// Loop through all the pixels in the imageData array, and modify // the red, green, and blue color values.

for(var i = 0,z=data.length;i<z;i++){

// The values for red, green and blue are consecutive elements // in the imageData array. We modify the three of them at once:

data[i] = ((data[i] < 128) ? (2*data[i]*data[i] / 255) : (255 - 2 * (255 - data[i]) * (255 - data[i]) / 255)); data[++i] = ((data[i] < 128) ? (2*data[i]*data[i] / 255) : (255 - 2 * (255 - data[i]) * (255 - data[i]) / 255)); data[++i] = ((data[i] < 128) ? (2*data[i]*data[i] / 255) : (255 - 2 * (255 - data[i]) * (255 - data[i]) / 255));

// After the RGB elements is the alpha value, but we leave it the same. ++i; }

// Putting the modified imageData back to the canvas. canvasContext.putImageData(imageData,0,0);

// Inserting the canvas in the DOM, before the image: image.parentNode.insertBefore(canvas,image); }

});