Request (more) correctly sized imgops preview image in Firefox

[paperboyo]

Because, unlike Chrome, Firefox differs screen.width with zoom, we need to treat it differently to correctly request screen-sized preview image.

Thanks @mbarton and @RichieAHB (who actually wrote all this).

• test on TEST

[RichieAHB]

Worth noting we wrote this in the GitHub editor so would be keen to make sure this was tested on CODE to make sure I didn't make any booboos.

Edit: I just saw @paperboyo 's checkbox 🙄

[RichieAHB]

Additionally I think this will serve large images on retina displays in Firefox (devicePixelRatio is 2 on retina displays) - this might not be a problem but Chrome won't get this special treatment.

[akash1810]

once tested on TEST 👍

[paperboyo]

@RichieAHB

this will serve large images on retina displays in Firefox

Shit! You’re right! I just checked on 27in Retina iMac and both browsers report 2560px screen.width but devicePixelRatio of 2 at 100% zoom and up it when zooming in. screen.width stays put in Chrome and differs on zoom in Firefox.

This is ridiculous! Forgetting performance considerations where we should maybe restrict image dimensions over certain limit and just wanting to serve 1:1 pixels to displays on different browsers – not sure what can we do apart from introducing even more absurd logic whereby if it’s ≥2 we would strip 2 and just take the rest?!

Thoughts?

[paperboyo]

OK. Tested on TEST, on Retinas too. This improves behaviour in Firefox on all dprs. Doesn’t change behaviour in Chrome on all dprs. Makes the browsers behave the same on non-HiDPI displays. Makes browsers widely different on HiDPI displays (Firefox gets Retina-ready images, Chrome gets half the physical resolution).
Above is true on a Mac, PC may deal with HiDPI differently (and OS has a much more granular scaling controls).

Until browsers vendors/spec writers agree, not much we can do, unless I’m wrong ¯_(ツ)_/¯