Is it better to use a canvas for a more efficient animation when changing the background image on pagescroll?

Question

Is it better to use a canvas for a more efficient animation when changing the background image on pagescroll?

I'm currently working on a parallax website that consists of a sequence of around 400 images. The background images change dynamically as the user scrolls through the page, creating a smooth animation effect. While I have managed to implement the scrolling functionality, I am encountering issues with the transition between background images not being seamless. There is a brief moment where a blank space is visible, depending on the internet connection speed. Additionally, the images are not being cached, leading to a new image request every time. I'm seeking advice on how to optimize the code to ensure smooth animation transitions without requesting new images each time and utilizing cached images effectively. I also explored using canvas for the animation, but encountered similar issues with image requests upon scrolling. Here is my current code structure for standard background image changing based on page scroll:

HTML

<div class="container">
    <div id="background-images" class="background-images">
        <div class="test"></div>
    </div>
</div>

CSS

#background-images{
    height: 4000px;
}
.container{
    border: 1px solid red;
    height: 400px;
    overflow: auto;
}
.test{
    position: fixed;
    top: 0;
    left: 0;
    z-index: 999;
    width: 600px;
    height: 600px;
}

Javascript

var $container = $(".container");
var $bgImage = $(".test");

// Attaching the scroll event to the background image
$container.scroll(function(event) {
    var position = $container.scrollTop();
    setBgImage(position);
});

// Preload the specified number of images for caching
function preload(totalImages) {
    for (var i = 0; i < totalImages; i++) {
        $('<img/>')[0].src = getImgUrl(i);
    }
}
preload(36); // Preload 36 images to be cached

// Set the background image based on scroll position
function setBgImage(position){
    var imageNum;
    var lineCount = 0;

    imageNum = parseInt(position  / 100);

    console.log("IMG: " + imageNum + ", Position: " + position);
    $bgImage.css("background-image", "url('" + getImgUrl(imageNum) + "')");
}

// Get the URL for the placeholder background image
function getImgUrl(num){
    return "http://placehold.it/200x200/&text=" + num;  
}

JSFiddle: http://jsfiddle.net/4j9u8qtf/1/

javascript jquery css scroll background-image

Answer 1

Answer №1

To display only the correct image and hide the rest, consider adding all images to the DOM but showing only the desired one using an actual image element instead of a CSS background image. I have made changes to your jsfiddle to illustrate this technique:

function create(totalImages) {
    for (var i = 0; i < totalImages; i++) {
        var img = $('<img/>');
        img[0].src = getImgUrl(i);
        $bgImage.append(img);
    }
    setBgImage(0);
}

create(37);

function setBgImage(position){
    var imageNum;
    var lineCount = 0;

    imageNum = parseInt(position / 100);

    console.log("IMG: " + imageNum + ", Position: " + position);

    $bgImage.find("img").hide().eq(imageNum).show();
}

http://jsfiddle.net/y92g7vvL/1/

Answer 2

To display only the correct image and hide the rest, consider adding all images to the DOM but showing only the desired one using an actual image element instead of a CSS background image. I have made changes to your jsfiddle to illustrate this technique:

function create(totalImages) {
    for (var i = 0; i < totalImages; i++) {
        var img = $('<img/>');
        img[0].src = getImgUrl(i);
        $bgImage.append(img);
    }
    setBgImage(0);
}

create(37);

function setBgImage(position){
    var imageNum;
    var lineCount = 0;

    imageNum = parseInt(position / 100);

    console.log("IMG: " + imageNum + ", Position: " + position);

    $bgImage.find("img").hide().eq(imageNum).show();
}

http://jsfiddle.net/y92g7vvL/1/

Answer 3

Answer №2

If you want to efficiently preload images, the best method is to utilize the Image constructor as shown in the example below. By using the Image constructor, there is no need to worry about attaching the images to the document for them to load.

function preload(url) {
  var image = new Image();
  image.src = url;
}

I have made changes to your Fiddle to incorporate this preload technique and eliminate the use of jQuery for setting the background-image. The result is that all images are now preloaded and loaded only once with improved performance.

$(function () {
    var $container = $(".container");
    var $bgImage = $(".test");
    var bgImage = $bgImage.get(0);

    $container.scroll(function (event) {
        var position = $container.scrollTop();
        setBgImage(position);
    });

    // preload the specified total number of images
    function preload(totalImages) {
        function fetch(url) {
          var image = new Image();
          image.src = url;
        }

        for (var i = 0; i < totalImages; i++) {
            fetch(getImgUrl(i));
        }
    }

    preload(36);

    function setBgImage(position) {
        var imageNum;
        var lineCount = 0;

        imageNum = parseInt(position / 100);
        var url = getImgUrl(imageNum);

        bgImage.style.backgroundImage = "url('"+ url +"')";
    }


    function getImgUrl(num) {
        return "http://placehold.it/200x200/&text=" + num;
    }
})

Answer 4

If you want to efficiently preload images, the best method is to utilize the Image constructor as shown in the example below. By using the Image constructor, there is no need to worry about attaching the images to the document for them to load.

function preload(url) {
  var image = new Image();
  image.src = url;
}

I have made changes to your Fiddle to incorporate this preload technique and eliminate the use of jQuery for setting the background-image. The result is that all images are now preloaded and loaded only once with improved performance.

$(function () {
    var $container = $(".container");
    var $bgImage = $(".test");
    var bgImage = $bgImage.get(0);

    $container.scroll(function (event) {
        var position = $container.scrollTop();
        setBgImage(position);
    });

    // preload the specified total number of images
    function preload(totalImages) {
        function fetch(url) {
          var image = new Image();
          image.src = url;
        }

        for (var i = 0; i < totalImages; i++) {
            fetch(getImgUrl(i));
        }
    }

    preload(36);

    function setBgImage(position) {
        var imageNum;
        var lineCount = 0;

        imageNum = parseInt(position / 100);
        var url = getImgUrl(imageNum);

        bgImage.style.backgroundImage = "url('"+ url +"')";
    }


    function getImgUrl(num) {
        return "http://placehold.it/200x200/&text=" + num;
    }
})

Answer 5

Answer №3

Experiment

coding tutorials

<div class="container">
    <div id="background-images" class="background-images">
        <div class="test"></div>
    </div>
</div>
<!-- hidden container for `img` elements -->
<div id="imgs"></div>

styling

#imgs {
  display:none;
}

javascript

$(function () {
    var $container = $(".container");
    var $bgImage = $(".test");

    $container.scroll(function (event) {
        var position = $container.scrollTop();
        setBgImage(position);
    });

    // preload a total number of images for optimization
    function preload(totalImages) {
        for (var i = 0; i < totalImages; i++) {
            $('<img/>', {
                "src": getImgUrl(i)
            })
            // append `img` elements to `#imgs` container
            // for image caching, 
            // preventing unnecessary requests
            .appendTo("#imgs");

        }
    }

    preload(36);

    function setBgImage(position) {
        var imageNum;
        var lineCount = 0;

        imageNum = parseInt(position / 100);

        console.log("IMG: " + imageNum + "
                   , Position: " + position
                   , $("#imgs img[src$=" + imageNum + "]"));

        // use existing cached images in DOM  
        // set background-image of `$bgImage`
        // from hidden `#imgs` `div`
        // images are not re-requested
        // on background-image adjustments
        $bgImage.css("background-image"
        , "url('" + $("#imgs img[src$=" + imageNum + "]").attr("src") + "')");
    }


    function getImgUrl(num) {
        return "http://placehold.it/200x200/&text=" + num;
    }
});

play around with the code http://jsfiddle.net/guest271314/bh91g0tv/

Answer 6

Experiment

coding tutorials

<div class="container">
    <div id="background-images" class="background-images">
        <div class="test"></div>
    </div>
</div>
<!-- hidden container for `img` elements -->
<div id="imgs"></div>

styling

#imgs {
  display:none;
}

javascript

$(function () {
    var $container = $(".container");
    var $bgImage = $(".test");

    $container.scroll(function (event) {
        var position = $container.scrollTop();
        setBgImage(position);
    });

    // preload a total number of images for optimization
    function preload(totalImages) {
        for (var i = 0; i < totalImages; i++) {
            $('<img/>', {
                "src": getImgUrl(i)
            })
            // append `img` elements to `#imgs` container
            // for image caching, 
            // preventing unnecessary requests
            .appendTo("#imgs");

        }
    }

    preload(36);

    function setBgImage(position) {
        var imageNum;
        var lineCount = 0;

        imageNum = parseInt(position / 100);

        console.log("IMG: " + imageNum + "
                   , Position: " + position
                   , $("#imgs img[src$=" + imageNum + "]"));

        // use existing cached images in DOM  
        // set background-image of `$bgImage`
        // from hidden `#imgs` `div`
        // images are not re-requested
        // on background-image adjustments
        $bgImage.css("background-image"
        , "url('" + $("#imgs img[src$=" + imageNum + "]").attr("src") + "')");
    }


    function getImgUrl(num) {
        return "http://placehold.it/200x200/&text=" + num;
    }
});

play around with the code http://jsfiddle.net/guest271314/bh91g0tv/

Answer 7

Answer №4

The repeated requests are due to the use of jQuery for setting background images, causing them to reload each time.

It may seem unnecessary to rely on jQuery in this scenario, as it can lead to unintended side effects that exacerbate your issue.

Simplify by directly configuring the X position of the background instead.

function offset_to(id, posX, posY) {
    document.getElementById(id).style.backgroundPosition = posX.toString() + 'px ' + posY.toString() + 'px';
}

Answer 8

The repeated requests are due to the use of jQuery for setting background images, causing them to reload each time.

It may seem unnecessary to rely on jQuery in this scenario, as it can lead to unintended side effects that exacerbate your issue.

Simplify by directly configuring the X position of the background instead.

function offset_to(id, posX, posY) {
    document.getElementById(id).style.backgroundPosition = posX.toString() + 'px ' + posY.toString() + 'px';
}

Answer 9

Answer №5

To give your image transition a smooth appearance, apply the following CSS transition properties:

.test{
    -webkit-transition: all 0.5s ease;
    -moz-transition: position 10s;
    -ms-transition: position 10s;
    -o-transition: position 10s;
    transition: all 0.8s ease;
}

Answer 10

To give your image transition a smooth appearance, apply the following CSS transition properties:

.test{
    -webkit-transition: all 0.5s ease;
    -moz-transition: position 10s;
    -ms-transition: position 10s;
    -o-transition: position 10s;
    transition: all 0.8s ease;
}

Is it better to use a canvas for a more efficient animation when changing the background image on pagescroll?

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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