Help adapting code for one slideshow so it supports two (multiple) on same page.

Help adapting code for one slideshow so it supports two (multiple) on same page.

This code I found works great for one slideshow, but I need to have two side-by-side and I'm a novice, so I can't see a good way to do this:


There are two slideshows (#dk-ad and #lt-ad) and they need to function independently of one another. There is probably an easy way to do this but since I'm a total hack I'll probably end up duplicating a lot of code and having it still not work anyway. I got roped into this by a friend who thinks I'm a genius even though I'm not.

Do I need to have 2 sets of variables for each slideshow? Then how do I pass this into the  createCanvasOverlay() function? Clueless. 

$(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 = $('#dk-ad li'),
current = 0,
slideshow = {width:0,height:0};

setTimeout(function(){

if(supportCanvas){
$('#dk-ad li img').each(function(){

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

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

$('#dk-ad .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 channels comes the alpha value, which we leave the same.
++i;
}

// Putting the modified imageData back on the canvas.
canvasContext.putImageData(imageData,0,0,0,0,imageData.width,imageData.height);

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

});