[whatwg] Media queries, viewport dimensions, srcset and picture

[Mike Gossmann]

When all the picture vs srcset started showing up on twitter, I was initially behind picture. I'm sure you all know the arguments for it, and I liked those arguments. Today though, I was reading an article about the two, and there was a misunderstanding about how srcset was working in the comments, and it made me realize that something closer to srcset would be ideal.

The big thing I realized is that as a developer, I do not want to write more media queries - or anything that works at all like them - into image elements. It's redundant. There's a good chance there's already a bunch of CSS in place controlling the shape and size of the image element itself, why should I have to write a bunch more, somewhere else, to control the src of the image too?

Why can't it work so that in the html I say here's an image, there's a version of it at 150x150, and a version at 48x48, and then in the CSS I say that the image is 25% of the width of the article it's in, which works out to 100px wide, and then the browser can just decide that the 150x150 would be best, and scale it down. If I change the CSS, I don't have to change the html too, the images I provided are still only available at those sizes. With image/picture sources set by viewport dimensions, even something as simple as adding more padding around articles on a site could involve going through all the HTML and adjusting the breakpoints in the tags. This way layout, units, and screen dpi, don't matter when writing the HTML,

I've seen people get confused and think srcset work this way, instead of by viewport size (unless I'm the confused one), and if they were right then srcset would work well for this. It would be even nicer if there was something even more CMS friendly, like:

<img src="/img/people.jpg" sizes="100x200 300x250 900x300" pattern="/tools/resizer.php?img=people.jpg&width={w}&height={h}" alt="A picture of some people.">

So src would be the fallback, then sizes would say which dimensions are available, in a fairly common format, using spaces to separate options like class does. pattern (probably a bad name) would be a template for the URL the browser can request the image from, replacing {w} and {h} with the requested dimensions. There wouldn't need to be a token for the dpi/resoultion/whatever, the browser could just request an image twice or three times or whatever the size. There's no point in having sizes="100x100 at 1 100x100 at 2 200x200 at 1" when you can just have sizes="100x100 200x200"

This gives the designer/developer full control over the shape and size of the image element (through CSS), while still allowing the browser to make decisions based on bandwidth and whatnot.

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Mike Gossmann | mike at c572.ca | http://gossmati.ca