Support responsive images in WP_Customize_Media_Control

[melchoyce]

When you add a custom logo, the preview in the Customizer sidebar isn't retina, even if the image file you uploaded is big enough.

Discovered in https://core.trac.wordpress.org/ticket/35942#comment:13. Some additional comments there.

Related:

• #21455: HiDPI (retina) theme custom backgrounds
• #36442: Customizer: when setting header image and site logo, also create a 2x image if possible

This is a bug in the way WP_Customize_Media_Control displays images, we should address it there.

There seem to be a couple of challenges here.

The backbone view for the WP_Customize_Media_Control relies on data modeled from wp_prepare_attachment_for_js(), i.e., the raw attachment data, which isn't necessarily the best model for rendering img elements by itself. We probably need to create a general use model that can be used for img data—much like wp.media.model.PostImage—where we could include methods for setting up attributes like src, srcset, sizes, etc. based on the raw attachment data.

We might be able to fudge it in the mean time by using additional attachment sizes to create a srcset attribute in the WP_Customize_Media_Control::content_template() view, but the template starts to become logic-heavy at a certain point, and maybe not worth it. I also worry about sites that have overridden the default sizes and turned some into hard-crops, which would cause the image to look skewed.

Add srcset and sizes to WP_Customize_Media_Control::content_template()

36191.patch​ updates the template in WP_Customize_Media_Control::content_template() to add srcset and sizes attributes when the relevant sizes are available. See my previous comment for caveats.

I like the idea of building out some more robust functions for the media models here. Especially since this control handles other types of media, adding a lot of image-size logic to the template is a bit messy as noted above. That being said, it could definitely work for a shorter-term solution. It won't make 4.5 anyway though, so maybe worth going for the better solution for 4.6 early.

Would reeeaaaally love to see this get some love. :) Non-retina logos are embarrassing.

It looks like this ticket has been focusing on the customizer UI; we could probably spin something off for frontend display separately without the questions around doing srcset in JS. For the output, it gets a bit complex with the way cropping happens, but my thought would be to double the size of the resize that happens after cropping to get a 2x version, then also make the 1x version as it currently does.

Replying to celloexpressions:

It looks like this ticket has been focusing on the customizer UI; we could probably spin something off for frontend display separately without the questions around doing srcset in JS. For the output, it gets a bit complex with the way cropping happens, but my thought would be to double the size of the resize that happens after cropping to get a 2x version, then also make the 1x version as it currently does.

That sounds good!

Adding svg-support for images would solve this problem, also with higher dpi than 2x (think about the future).