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The WordPress 4.4 adds multiple image sizes with srcset when using the_post_thumbnail function. Is it possible to get only one image size without srcset ?

I understand that it is possible to add a filter to disable srcset from all images, but I want to disable the srcset only when calling a specific thumbnail size (for example only when calling full image size).

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I want to disable the srcset only when calling a specific thumbnail size (for example only when calling full image size).

Here are two ideas (if I understand you correctly):

Approach #1

Let's check the size from the post_thumbnail_size filter. If it matches a corresponding size (e.g. full) then we make sure the $image_meta is empty, with the wp_calculate_image_srcset_meta filter. That way we can bail out early from the wp_calculate_image_srcset() function (earlier than using the max_srcset_image_width or wp_calculate_image_srcset filters to disable it):

/**
 * Remove the srcset attribute from post thumbnails 
 * that are called with the 'full' size string: the_post_thumbnail( 'full' )
 *
 * @link http://wordpress.stackexchange.com/a/214071/26350
 */
 add_filter( 'post_thumbnail_size', function( $size )
 {
     if( is_string( $size ) && 'full' === $size )
         add_filter( 
             'wp_calculate_image_srcset_meta',  
              '__return_null_and_remove_current_filter' 
         );   
    return $size;
 } );

// Would be handy, in this example, to have this as a core function ;-)
function __return_null_and_remove_current_filter ( $var )
{
    remove_filter( current_filter(), __FUNCTION__ );
    return null;
}

If we have:

the_post_thumbnail( 'full' );

then the generated <img> tag will not contain the srcset attribute.

For the case:

the_post_thumbnail();

we could match the 'post-thumbnail' size string.

Approach #2

We could also add/remove the filter manually with:

// Add a filter to remove srcset attribute from generated <img> tag
add_filter( 'wp_calculate_image_srcset_meta', '__return_null' );

// Display post thumbnail
the_post_thumbnail();

// Remove that filter again
remove_filter( 'wp_calculate_image_srcset_meta', '__return_null' );
  • you probably need to also remove the wp_calculate_image_srcset_meta filter when the function ends – Mark Kaplun Jan 8 '16 at 14:43
  • I added the approach where we add/remove the filter callback manually. I use the instance counting in the other approach to run it only once for each the_post_thumbnail() call @MarkKaplun – birgire Jan 8 '16 at 15:02
  • I simplified the code snippet, thanks for letting me think about this again ;-) @MarkKaplun – birgire Jan 8 '16 at 15:48
  • 1
    :) I just found a productive way to show my dislike to anonymous functions in filters :) – Mark Kaplun Jan 8 '16 at 15:51
  • 1
    or there should be a "run one time" parameter to add_filter. This pattern is really common. – Mark Kaplun Jan 8 '16 at 16:09

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