[wp-trac] [WordPress Trac] #40469: How to remove full size image path from srcset and more intelligent choices in srcset candidate list

[WordPress Trac]

#40469: How to remove full size image path from srcset and more intelligent choices
in srcset candidate list
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 Reporter:  lisota           |      Owner:
     Type:  enhancement      |     Status:  new
 Priority:  normal           |  Milestone:  Awaiting Review
Component:  Post Thumbnails  |    Version:  4.7.3
 Severity:  normal           |   Keywords:
  Focuses:                   |
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 On our site, we have a number of image sizes registered in WP, in addition
 to the default ones, for a variety of purposes. A large one to fill the
 width of our column, smaller ones for some custom image output, etc.

 The result of this is a sloppy srcset candidate list filled with URLs that
 may make no logical sense in a particular location in the markup. WP does
 have an upper size limit to prevent giant images from being in srcset, and
 also matches aspect ratio, but nothing else.

 I have been able to hack together a filter using
 `wp_calculate_image_srcset_meta` to unset various sizes in the `sizes`
 array. But if the full size of the image is smaller than the
 `max_srcset_width` parameter, it still gets included, and there should be
 some way to remove it. The full size of the image is not part of the
 `sizes` array in image_meta.

 It actually points to a larger issue with WP srcset implementation, which
 is that is mindlessly fills the HTML with srcset candidates that in many
 instances would never be used, adding lots of excess markup that a
 developer wouldn't add.

 For example, we have a 300px wide sidebar where we output an image. The
 sidebar is never larger than 300px, and even is that size in our
 responsive site on mobile. The srcset outputs a 150px, 200px, 300px,
 600px, 768px and 1240px, based on the sizes registered in our installation
 and the built-in ones. Logisitically, all that is really needed for this
 layout is 300px and probably the 600px version. We have all sorts of
 examples like this where the srcset includes either smaller or larger
 sizes than are physically possible in a given layout.

 Obviously WordPress cannot know how a site is styled, but it feels like
 there needs to be a more robust way of dealing with this. It is not a
 great feature to load up on unneeded markup.

 As a theme developer, I would like the ability to constrain the srcset
 candidate list in an intelligent way each time I output img tags into the
 markup. It is easy for me to say "at this location, this image will never
 be smaller than 300px, so don't give me anything smaller, and will also
 never be bigger than 300px, so only go up to a 2x version and skip
 anything larger.

 I'm guessing this is exacerbated by a variety of themes and pluging that
 may load up on extra registered image sizes as well.

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Ticket URL: <https://core.trac.wordpress.org/ticket/40469>
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