In this tutorial we will build a photo gallery and enhance it with html5 canvas and css3 transitions. See the demo and try the hover effect. The grayscale “copies” of the images are created with canvas and we use pure css3 for the smooth changes.
Download the source files
Portfolio gallery with canvas
.zip 0.25MB
Step 1 : Html markup
Let’s start with a simple markup, each portfolio entry being an element of an unordered list.
<!DOCTYPE html> <html> <head> <meta charset="UTF-8" /> <title>Gallery :: Tutorial by PeHaa </title> <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script> </head> <body> <div id="wrap"> <h1>Gallery</h1> <ul id="gallery"> <li><a href=""><img src="images/flo1.jpg"><div>Spring flowers 1</div></a></li> <li><a href=""><img src="images/lights2.jpg"><div>City lights 1</div></a></li> <li><a href=""><img src="images/flo3.jpg"><div>Spring flowers 2</div></a></li> <li><a href=""><img src="images/lights1.jpg"><div>City lights 2</div></a></li> <li><a href=""><img src="images/flo2.jpg"><div>Spring flowers 3</div></a></li> <li><a href=""><img src="images/lights3.jpg"><div>City lights 3</div></a></li> </ul> <p>Photos by <a href="http://pinkonhead.com">Pinkonhead</a></p> </div> </body> </html>
Step 2: Basic styles
We start our stylesheet with a basic reset.
html, body, div, span, h1, h2, p, a, ul, li, img
{margin: 0; padding: 0;
border: 0; outline: 0;
font-size: 100%;background: transparent;}
ul {list-style: none;}
:focus {outline: 0;}
a {text-decoration:none;}
We will use 300px x 300px images. The main containing element #wrap is centered up (margin: 0 auto) and given the width of 1020px (=340 x 3).
The list items are given float : left and are positioned relatively. The image title is wrapped in a div element that slides up on hover. To achieve a smooth effect we apply a css3 transition.
(Note that for the simplicity of this tutorial I don’t use any vendor prefixes. Therefore, you’ll find them in the source file to download).
#wrap {
width: 1020px;
margin: 0 auto;
}
li {
float:left;
position:relative;
display:inline-block;
width:300px;
height:300px;
margin:10px;
padding:10px;
background:#fff;
box-shadow:0 0 5px rgba(0,0,0,.35);
}
li div {
position:absolute;
height:0;
width:280px;
background:rgba(0,0,0,.45);
overflow:hidden;
bottom:10px;
left:10px;
padding: 0 10px;
line-height:50px;
color:#fff;
transition:height 1s;
}
li:hover div {
height:50px;
}
Click on the image to below to see the result at the current stage.
Step 3: Canvas
Now, we will make use of the html5 canvas element to draw the grayscale versions of our images. Below you’ll find a createCanvas custom function that creates a canvas element, takes a copy of an image, performs the conversion and draws it to the canvas and finally inserts the canvas to the DOM where desired. With .each() method the createCanvas function is iterated across all images within the #gallery list.
$(window).load(function() {
$('#gallery img').each(function() {
createCanvas(this);
});
function createCanvas(image) {
var canvas = document.createElement('canvas');
if (canvas.getContext) {
var ctx = canvas.getContext("2d");
// specify canvas size
canvas.width = image.width;
canvas.height = image.height;
// Once we have a reference to the source image object we can use
// the drawImage(reference, x, y) method to render it to the canvas.
//x, y are the coordinates on the target canvas where the image should be placed.
ctx.drawImage(image, 0, 0);
// Taking the image data and storing it in the imageData array.
//You can read the pixel data on a canvas using the getImageData() method.
// Image data includes the colour of the pixel (decimal, rgb values) and alpha value.
// Each color component is represented by an integer between 0 and 255.
//imageData.data contains height x width x 4 bytes of data, with index values ranging from 0 to (height x width x 4)-1.
var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height),
pixelData = imageData.data;
// Loop through all the pixels in the imageData array, and modify
// the red, green, and blue color values.
for (var y = 0; y < canvas.height; y++) {
for (var x = 0; x < canvas.width; x++) {
// You can access the color values of the (x,y) pixel as follows :
var i = (y * 4 * canvas.width) + (x * 4);
// Get the RGB values.
var red = pixelData[i];
var green = pixelData[i + 1];
var blue = pixelData[i + 2];
// Convert to grayscale. One of the formulas of conversion (e.g. you could try a simple average (red+green+blue)/3)
var grayScale = (red * 0.3) + (green * 0.59) + (blue * .11);
pixelData[i] = grayScale;
pixelData[i + 1] = grayScale;
pixelData[i + 2] = grayScale;
}
}
// Putting the modified imageData back on the canvas.
ctx.putImageData(imageData, 0, 0, 0, 0, imageData.width, imageData.height);
// Inserting the canvas in the DOM, before the image:
image.parentNode.insertBefore(canvas, image);
}
}
});
Step 4: Styling the canvas
If you look into the generated code source you’ll find
<ul id="gallery"> <li><a href=""><canvas width="300" height="300"></canvas><img src="images/flo1.jpg"><div>Spring flowers 1</div></a></li> <li><a href=""><canvas width="300" height="300"></canvas><img src="images/lights2.jpg"><div>City lights 1</div></a></li> <li>...</li> ... </ul>
Let’s add some styling to define the canvas behavior in normal and hover state:
canvas {
opacity:1;
position:absolute;
top:10px;
left:10px;
transition:opacity 1s .2s;
}
li:hover canvas {
opacity:0;
}
And that’s it ! This example will not work in Internet Explorer versions below 9. You could provide an alternative solution using grayscale filter and adding some jQuery to recreate the transition effect on hover – but this part is not covered in this tutorial.
The beautiful photos featured here were taken by Pinkonhead, and are shared as freebies on her blog. Enjoy.
