wp_get_attachment_image with custom size not rendering possible 2x srcset image

Question

I'm noticing a difference (bug?) in how WP is rendering srcset images now.

If I register my image sizes with

add_image_size('single_featured_image', 1280, 9999, false);
add_image_size('single_featured_image_2X', 2560, 9999, false);

and confirm the files generated

test-image-1280x720.jpg test-image-2560x1440.jpg

and then attempt to render them with

          echo wp_get_attachment_image(
                get_post_thumbnail_id(),
                'single_featured_image',
                false,
                [
                  'class' => 'object-cover object-center w-full h-full'
                ]
              );

HTML rendered is

<img width="1280" height="720" src="http://wauble.lndo.site/wp-content/uploads/2023/07/test-image-2-1280x720.jpg" class="object-cover object-center w-full h-full" alt="" decoding="async" loading="lazy" srcset="http://wauble.lndo.site/wp-content/uploads/2023/07/test-image-2-1280x720.jpg 1280w, http://wauble.lndo.site/wp-content/uploads/2023/07/test-image-2-300x169.jpg 300w, http://wauble.lndo.site/wp-content/uploads/2023/07/test-image-2-1024x576.jpg 1024w, http://wauble.lndo.site/wp-content/uploads/2023/07/test-image-2-768x432.jpg 768w, http://wauble.lndo.site/wp-content/uploads/2023/07/test-image-2-1536x864.jpg 1536w, http://wauble.lndo.site/wp-content/uploads/2023/07/test-image-2-2048x1152.jpg 2048w, http://wauble.lndo.site/wp-content/uploads/2023/07/test-image-2-18x10.jpg 18w" sizes="(max-width: 1280px) 100vw, 1280px">

Notice 2560x is not included in the srcset values.

I'm assuming there is some proportion matching going on. What's strange is I used to use this technique all the time and always seemed to work.

I can get the 2x image included in srcset values if instead of using the image name handle I use the int[] for image size argument in my wp_get_attachment_image call.

       echo wp_get_attachment_image(
                get_post_thumbnail_id(),
                [1280, 9999],
                false,
                [
                  'class' => 'object-cover object-center w-full h-full'
                ]
              );

No real problem I guess, just seems a little silly that I have to name it in the first place. I apologize if I'm doing something dumb here....and I hope that's the case.

Any help appreciated!

Answer 1

It appears the problem was that image size variants were being capped by the max_srcset_image_width property that can be raised with the following:

add_filter( 'max_srcset_image_width', 'setSrcsetMaximumWidth', 10, 2 );

function setSrcsetMaximumWidth( $max_srcset_image_width, $sizes_array ) {
  return 3200;
}

I was never aware of this before and have no idea why I never ran into this.