Contao: Set width and height attributes as an aspect ratio for images

[ausi]

Browsers now seem to change the behavior of how width and height attributes are handled in combination with responsive CSS, see https://github.com/whatwg/html/pull/4952

The new behavior seems to be the way that @fritzmg already suggested five years ago in https://github.com/contao/core/issues/7500#issuecomment-65933582 which means you can use width and height now to define an aspect ratio for the image.

To improve our usage of this feature in Contao we should now always use width and height attributes as long as all <source>s have the same aspect ratio.

This is a bugfix IMO because the behavior of browsers has changed.

For more details about the changes see https://bugzilla.mozilla.org/show_bug.cgi?id=1547231, https://bugs.chromium.org/p/chromium/issues/detail?id=979891, https://bugs.webkit.org/show_bug.cgi?id=201641, https://twitter.com/tomayac/status/1165902659083280384, https://www.youtube.com/watch?v=4-d_SoCHeWE.

There are also plans to add width and height support for <source> tags in the future, see https://github.com/whatwg/html/issues/4968

[leofeyer]

What exactly needs to be changed on our end?

[ausi]

To improve our usage of this feature in Contao we should now always use width and height attributes as long as all <source>s have the same aspect ratio.

I will provide a pull request once we agreed on bugfix vs. feature 🙃

[leofeyer]

I guess this is a bugfix.

[Toflar]

Bugfix

[ausi]

Pull requests: #940 (4.8) #939 (4.8)

We should probably wait until one of the browsers released a stable version with this feature activated. Firefox 71 will be released in december AFAIK.

[leofeyer]

Would it break something if we released it now?

[ausi]

It shouldn’t break something in general IMO. There might be some edge cases with using the sizes attribute, but they should be easy to fix with CSS I think.

I’d still wait for the first released browser version to be more certain that this new behavior stays, and so that we can test our implementation.

[fritzmg]

I did find a problem. Consider the following setup:

Before, the output of this image size was

<img src="…" srcset="… 400w, … 800w" sizes="(max-width: 780px) 400px, 800px" alt="" itemprop="image">

Now, the output is

<img src="…" srcset="… 400w, … 800w" sizes="(max-width: 780px) 400px, 800px" alt="" itemprop="image" width="400" height="267">

This causes the image to be shown like this:

Instead of this:

And there seems to be no correct solution for this, because if you turn the values around like this:

The Browser will blow up the 400px image to 800px (or less, within its parent) if the viewport is 780px or lower.

[contaoacademy]

I also noticed the same behavior yesterday after the update to 4.8.7.

At the moment I have helped myself as follows:

[fritzmg]

@contaoacademy in your case there should be no problem, regardless of what you actually put into the density/scaling.

[contaoacademy]

My old setting was "Breite" 320.

[fritzmg]

My old setting was "Breite" 320.

Yes, that causes the problem in conjunction with your sizes attribute. The density/scaling is irrelevant.

[ausi]

@fritzmg If you set the width to 400 isn’t it correct if it is shown with that width in the front end? I think you have to set width: 100%; height: auto; for your image in that case.

Can you please also try if width: auto; height: auto; would fix your issue?

[fritzmg]

@fritzmg If you set the width to 400 isn’t it correct if it is shown with that width in the front end

Not if the sizes attribute says otherwise, at least that is what I would expect. The width and height attribute are supposed to give the browser the correct aspect ratio information of the image, but the actual size should be determined by a multitude of factors.

What does the specification say about an image with the following markup:

<img src="…" srcset="…" sizes="(max-width: 780px) 400px, 800px" width="400" height="200">

https://jsfiddle.net/v5xj9krz/

Should it be displayed with a width of 800px or 400px, inside a viewport that is 781px or more? I expected it to be displayed with a width of 800px as defined in the sizes attribute. But it is actually displayed with a width of 400px.

Can you please also try if width: auto; height: auto; would fix your issue?

Seems to have no effect: https://jsfiddle.net/3g4evour/

[ausi]

Can you please also try if width: auto; height: auto; would fix your issue?

Seems to have no effect: jsfiddle.net/3g4evour

It should work with the correct srcset: https://jsfiddle.net/jmvq1sc8/

So I think adding img { width: auto; height: auto; } to your CSS would be the correct solution for your use case. I’m not sure if we can or should inject this CSS automatically.

[fritzmg]

Yeah, you are right 😃

Imho this change should be reverted and added to 4.9 instead. Plus a mention in the UPGRADE.md.

[ausi]

I’m not sure if we should revert it. IMO using sizes to set the width of an image is not recommended and probably doesn’t affect too much installations.

As the fix is very simple by adding img { width: auto; height: auto; } I think the improvement in performance outweighs the small behavior change, don’t you think?

[fritzmg]

I’m not sure if we should revert it. IMO using sizes to set the width of an image is not recommended and probably doesn’t affect too much installations.

I use it all the time and I was unaware that this is not recommended. To be fair, it won't affect any of our installations, as our CSS base includes img { width: auto; height: auto; } anyway but still.

[fritzmg]

As the fix is very simple by adding img { width: auto; height: auto; } I think the improvement in performance outweighs the small behavior change, don’t you think?

Imho this change causes too many problems for a bugfix release and seems unnecessary with 4.9 right around the corner. At least with 4.9 we can properly advertise the change.

[leofeyer]

@contao/developers What are your opinions on this one?

[ausi]

I’m OK with both (keeping as is or revert the change) with a slight tendency to keeping it as is.

[leofeyer]

I’m not sure if we should revert it. IMO using sizes to set the width of an image is not recommended and probably doesn’t affect too much installations.

I am with @ausi on this one.

[aschempp]

I’m not sure if we should revert it. IMO using sizes to set the width of an image is not recommended and probably doesn’t affect too much installations.

What are sizes recommended for then?

[ausi]

What are sizes recommended for then?

To tell the browser which resource to load.

[aschempp]

ah, well that was a synonym for "with of the image" to me. 👍

[fritzmg]

IMO using sizes to set the width of an image is not recommended and probably doesn’t affect too much installations.

Can you elaborate on this? To me it seems like a perfectly valid use-case, and it is supported by the HTML standard as well, is it not?

[ausi]

The spec writes “The <source-size-value> gives the intended layout width of the image.”

The examples in the spec state: “In this example, a banner image takes up the entire viewport width (using appropriate CSS).” and “These sizes do not necessarily have to match up exactly with the actual image width as specified in the CSS.”

I couldn’t find a specific statement that says something like “The sizes attribute shouldn’t be used for styling, use CSS instead.” but I think this can inferred from the examples in the specification.

it is supported by the HTML standard as well, is it not?

The HTML standard tells browsers to convert w descriptors to x descriptors by dividing it by the size from the sizes attribute. Technically this results in the density-corrected intrinsic width being the same as the size from sizes. But I don’t think this means setting the width using sizes is supported, also because it only works with px values and not with a responsive/fluid design.

If my interpretation of the spec is wrong here I would still favor the solution using img { width: auto; height: auto; } because of the performance benefits.

[ausi]

As discussed on Mubmle: We (I) should adapt the help text for the sizes attribute to point out that it should not be used for sizing the image, but only tell the browser which resource it should load.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[ausi]

This is on my todo list.

[ausi]

We (I) should adapt the help text for the sizes attribute to point out that it should not be used for sizing the image, but only tell the browser which resource it should load.

Done in #1807