0Show enlarged image on hover in wordpress

As part of the recent improve­ments I’ve been mak­ing to vari­ous web­sites I wanted to make images in gal­ler­ies show enlarged ver­sions when hovered over. Doing this with basic CSS is fairly trivi­al, but I did­n’t just want to expand the ori­gin­al image, I wanted the browser to grab a new (lar­ger) image too…

All of the images are already provid­ing a full src-set so all I needed to do was to use a little jQuery (which is already loaded by word­press any­way) to change the tar­get dis­play size to make the browser pull a lar­ger image. The nice thing is that the CSS works instantly so you get a lar­ger image using the ori­gin­al file, and then the qual­ity improves a split second later as the high­er res file gets loaded.

The CSS

The CSS I used is as fol­lows. I simply added this to the style.css of my theme (or rather child-theme — always a good idea to use one)

dt.gallery-icon a img.size-thumbnail:hover
{
transform: scale(3.0);
}

Note (1) — the above CSS applies to gal­lery images only. It is unlikely any­one would want this func­tion­al­ity for all images dis­played any­where on the page, but you might want it for the main con­tent sec­tion. You would need to check how your theme struc­tures this, but in my case the main con­tent area is a “sec­tion” so the fol­low­ing code would do the job

section.entry-content p a img.size-thumbnail:hover
{
transform: scale(3.0);
}

Note (2) — This code applies only to thumb­nail images. For medi­um images you would replace “size-thumb­nail” with “size-medi­um”, and for large with “size-large”.

Note (3) — Because my thumb­nails are 120x80px I want to increase them to 3x their ori­gin­al size. I already have a cus­tom image size of 360×240 that word­press cre­ates for me that is included in the src-set. For hi-dpi screens there are also even lar­ger image sizes that I have (e.g. 720×480). Cre­at­ing addi­tion­al image sizes in word­press is easy — there are lots of good guides online if you need to do this.

If you wanted to scale to 1.5x or 2.0x simple change the 3.0 as desired

The jQuery

Add the fol­low­ing to your (child) theme’s script file (assum­ing it has one). If it does­n’t have one, cre­ate your own, and ‘enqueue’ it with a cus­tom func­tion in the (child) theme’s functions.php

jQuery(document).ready(function(){

  jQuery("dt.gallery-icon a img.size-thumbnail").hover(function(){
    jQuery(this).attr("sizes","(max-width: 360px) 100vw, 360px");
    }, function(){
    jQuery(this).attr("sizes","(max-width: 120px) 100vw, 120px");
  });

  //repeat the above 5 lines here for each different image size you want to modify

});

The above code is apply­ing to images with class thumb­nail that are found inside any dt with a gal­lery-icon class — so in oth­er­words — only to images inside the word­press built-in gal­lery struc­ture. On hov­er the max-width is increased from 120 to 360 (a 3x increase to match my CSS!), and then the second part of the func­tion restores the ori­gin­al 120 width when the hov­er stops.

As with the CSS above, you can adjust the num­bers to change how much the image enlarges, and you can change the dt.gallery-icon a img.size-thumbnail sec­tion to tar­get a dif­fer­ent ele­ment or class depend­ing on which images you want to target.

Enqueue your own script

If your theme did­n’t have a script file and you need to enqueue your own add the fol­low­ing to your (child) theme’s functions.php (assum­ing you called your script file image-zoom.js and saved it in the root folder of the theme)

wp_register_script( 'img-zoom', get_stylesheet_directory_uri() . '/image-zoom.js', array( 'jquery' ), '', true);
wp_enqueue_script( 'img-zoom' );

The above will register your script, in the foot­er, mak­ing sure it is placed after jquery (so jquery should already be avail­able when it executes)

Adding image sizes

For com­plete­ness here’s how to add cus­tom image sizes to word­press. Again, add this to your (child) theme’s functions.php

add_image_size( 'quarter-width', 192, 144, false );

Above I’ve added a new image-size called “quarter-width” with a max­im­um width of 192px and a max­im­um height of 144px. The image will not be cropped (hence the false at the end).

Word­Press will now cre­ate images of this size auto­mat­ic­ally when you upload images (you will need to use a thumb­nail rebuild plu­gin to recre­ate the thumb­nails for already-uploaded images).

This new image size will NOT show up for inser­tion in the edit­or though. To make it avail­able also add the fol­low­ing code to your functions.php

function my_custom_image_sizes( $sizes ) {
    return array_merge( $sizes, array(
        'quarter-width' => __('Quarter Width'),
    ) );
}

Respecting existing settings

One more thing that you might want to do (to ensure respons­ive images work well) is to cre­ate lar­ger (i.e. hi-dpi) thumb­nail sizes that respect the GUI of wheth­er to crop thumb­nails or not. To do that use the code below which as you will see is slightly mod­i­fied from the more basic one above

add_image_size( 'resp-thumb-2x', (get_option( 'thumbnail_size_w' ) == 0 ? 0 : '240'), 160, get_option( 'thumbnail_crop' ) );

The above code checks for 2 things — firstly it checks to see if the crop option is set, and if it is, it mir­rors it for our new respons­ive size. It also checks to see if the width is set to 0 (i.e. no max­im­um) in which case our new image will also have no max­im­um either. I called the new image size “resp-thumb-2x” as it is a ‘respons­ive’ copy of the thumb­nail that is twice as large (for hi-dpi screens with double the nor­mal pixel dens­ity). I have also cre­ated a num­ber of oth­er sizes to make a fairly com­plete set.

Note — Since my ori­gin­al thumb­nails were 120×80 I want my new ones to be 240×160 so those are the sizes I have spe­cified (hard-coded). It would be pos­sible to get both the height and width spe­cified for the ori­gin­al thumb­nail and mul­tiply both by 2 to make this func­tion fully gen­er­ic, but I did­n’t do so when I was devel­op­ing it so I will leave that to you to fig­ure out!

One final tip

If, like me, you cre­ate your own full set of new image sizes, you may not want word­press to cre­ate it’s own extra hid­den sizes. In addi­tion to the ori­gin­al image, and the thumb­nail, the medi­um, and the large image, word­press also cre­ate a “post-thumb­nail”, a “medi­um-large”, a 1536×1536 and a 2048×2048. These are dis­abled in 2 dif­fer­ent ways…

To remove the 1536 en 2048 images is straight-forward

remove_image_size( '1536x1536' ); //remove the 1536 we dont need it
remove_image_size( '2048x2048' ); //remove the 2048 we dont need it

The post-thumb and medi­um-large are slightly more complicated

//remove the built-in medium-large
add_filter('intermediate_image_sizes', function($sizes) {
    return array_diff($sizes, ['medium_large']);
});

//remove the built-in post-thumbnail
add_filter('intermediate_image_sizes', function($sizes) {
    return array_diff($sizes, ['post-thumbnail']);
});

Note that remov­ing the post-thumb­nail seems to some­times have strange effects on the image lib­rary in the editor.

One final final note

When decid­ing on image sizes (for lar­ger images, less so thumb­nails) you ideally want a size that com­mon aspect ratio images will always res­ize nicely to. For that reas­on I recom­mend the fol­low­ing sizes

Note how the widths spe­cified pro­duce whole num­ber heights for all 3 of the most com­mon aspect ratios. You won’t get that with widths like 150 or 200.

Also note the pat­tern in increases. Jump 2 rows in the table and the size doubles! The even rows (288,576,1152 en 1535) are also 1.5x the pre­vi­ous size so these work well on semi-hi-dpi screens using a 50% dpi increase. By using this set of 7 sizes you have a good range of usable options for most view­ports AND a good set of respons­ive images that word­press will auto­mat­ic­ally add to the src-set since they will have con­sist­ent aspect ratios with no frac­tions that would lead to qual­ity loss or cropping.

Cur­rently for thumb­nails I tend to either have unlim­ited width allowed OR I hard crop to a fixed 3:2 ratio so I use whole num­ber sizes for thumb­nails but I may even­tu­ally tweak my theme and extend the above sys­tem back­wards by hav­ing options 48px and 96px wide (note there is no value between these 2 that would work unfor­tu­nately — and since I use 60px wide mini thumb­nails I haven’t opted to extend back­wards). 72px would work for both 4:3 en 3:2 (and 64px would work with 4:3 en 16:9). Since a major­ity of my images are taken on my dSLR these are typ­ic­ally 3:2 (the same as the aspect ratio of tra­di­tion­al 35mm film) so I could use this size as well, which would then work with the large sizes all the way up, but the lar­ger sizes are not cropped where­as my thumb­nails are — I’m happy for lar­ger images to be both land­scape and por­trait, but I want thumb­nails to typ­ic­ally be land­scape only to fit with my design, so that’s why I haven’t exten­ded back­wards. Hope­fully as more and more logos are avail­able as SVG’s, and once JPEG-XL arrives in browser in the near future, a lot of this will be resolved.