Responsive image with srcset and preloading images

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19 Sep, 2016 01:36 PM

Hi Dmitry!

I'm trying to figure this out, but I'm stuck.

I have a page with a full screen size slider ( which is working well.

For responsive reasons, I'm using the srcset attribute with multiple image sizes so the browser can choose which image to load which fits best. My code:

<img srcset="480x319.jpg 320w, 640x426.jpg 480w, 960x639.jpg 640w, 1280x852.jpg 960w, 1920x1277.jpg 1280w, 3200x2129.jpg 1920w" src="1280x852.jpg" class="rsImg" />

But, the preloade function only preloads the default sizes, the 1280x852.jpg images... and all the other images are loaded.

Any idea how to change this? Specially on big screens where the big images are used it would be great of not all the images are loading, but only one by one... :)

thanx in advance!

  1. Support Staff 1 Posted by Dmitry Semenov on 19 Sep, 2016 04:14 PM

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    You can not use IMG element if you want images to lazy-load, as browser will start loading them even before JS is executed.

    You need to create IMG elements with srcset dynamically as slides change, here is an example


  2. 2 Posted by info on 20 Sep, 2016 09:33 AM

    info's Avatar

    Briljant, just what I needed, it works like a charm. Thanx Dmitry!

  3. 3 Posted by info on 20 Sep, 2016 12:15 PM

    info's Avatar

    I was a little bit to fast. The script is working but I can't get the slider to load the images in imageScaleMode: "fill". Instead of centering them nicely horizontal en vertical they don't.
    See the develop version:

    I want the images to load like in this version:
    both centered horizontal and vertical. In this version I used the setting imageScaleMode: "fill"

    Ay idea how to get the same result with the dynamically added slides? In some way they don't get the inline style like

    <code>style="width: 1563px; height: 1040px; margin-left: -207px; margin-top: 0px;"</code>

  4. Support Staff 4 Posted by Dmitry Semenov on 20 Sep, 2016 03:07 PM

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    As you're modifying content of a slide dynamically and not with rsImg element, there is no option to apply built-in scaling. There are a few solutions:

    var hRatio = sliderWidth / imageWidth;
    var vRatio = sliderHeight / imageHeight;
    var fillRatio = hRatio > vRatio ? hRatio : vRatio;
      width: imageWidth * fillRatio,
      height: imageHeight * fillRatio,
      marginTop: ( sliderHeight - imageHeight * fillRatio) / 2,
      marginLeft: ( sliderWidth - imageWidth * fillRatio) / 2

    (example - )

    but you'll need to predefine image dimensions in markup (from backend, e.g. via attribute), as preloading image with srcset is unreliable - you'll often get incorrect image naturalWidth/naturalHeight.

  5. 5 Posted by info on 23 Sep, 2016 07:59 AM

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    Thanx for the tip, I’ve got it working with the JS algorithm!

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  6. 6 Posted by plantsbook on 27 Aug, 2017 09:08 AM

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    Hello, Dmitry.
    Your example ( works
    but only for one slideshow on the page.
    If there are two slideshows on one page
    only first works and second loads just first images.
    Is there a solution for multiple slideshows?

  7. Support Staff 7 Posted by Dmitry Semenov on 27 Aug, 2017 12:48 PM

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    @plantsbook, create an each loop, e.g. like so

  8. 8 Posted by plantsbook on 27 Aug, 2017 02:06 PM

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    Thank you.
    Works perfect.

  9. 9 Posted by plantsbook on 24 Oct, 2017 01:05 PM

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    Again, if there are two slideshows on one page, second slideshow don't have height (only height of bottom margin from css). You can see it only for the first time page loads, or if you clear cache and open page again. Maybe you know the solution for that problem? example

  10. Support Staff 10 Posted by Dmitry Semenov on 24 Oct, 2017 04:13 PM

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