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Comment by martin_a | Hacker News Reader

How/Why would I do this with responsive/fluid layouts and dynamically changing image sizes?

How/Why would I do this with responsive/fluid layouts and dynamically changing image sizes?

You don't.

You're not required to use it on every image. It's a completely optional parameter that you add to individual images that might benefit from it.

You can use it on navigation icons that don't change size. Maybe in some of your boilerplate in the footer. Or in some sidebar content or a testimonial that you control. But if you have images of unknown size populating the middle of the page, don't use it on those.

But isn't that exactly the use case of lazy loading and also the source of all those problems?

The 1.2 kB icon in the footer is not really a problem, but the xxx kB article image some author uploaded with unknown sizes.

Those things will make my page jump around and will need to be lazy-loaded.

It should be possible in most backends to get size information from the image at the time of uploading. A pair of integers shouldn't be a lot of data to store as metadata for your HTML rendering process.

Use media conditions and source sets. https://developer.mozilla.org/en-US/docs/Learn/HTML/Multimed...

You would attempt to set some constraints on the image dimensions at the different breakpoints. For example, you can use percentages if you want a fluid amount. It's really to tell the browser how much space to allocate to the image before it's loaded. This is an old problem and pages that jump around would happen on slower connections.

Oh, constraints! These cute little math things that always work and are fundamental to the definition of layout geometry.

I doubt we’ll ever see them built into a browser, because all nice generalized things never get there.

Ok, my image has 100% width for screens up to 800 px width, what height value do I have to set? You simply don't know this information at the time when the DOM is built.

The idea to set fixed dimensions feels like it comes from a time where we did designs with tables and "optimized" sites for 1024 x 768 pixel screen size.

That was the time when you could tell that this image should be displayed 200 x 200 px in size and nothing else. And it fit. One way or another.

I would approach this thinking in terms of a known aspect ratio of the images and use a technique like this:

https://www.w3schools.com/howto/tryit.asp?filename=tryhow_cs...

Make no mistake, this is a silly problem to need to hack a solution for. So I would welcome lazy loaded images with space allocation before it's rendered with a responsive sizing.

Use the browser's onresize event to work out what changed and modify the width and height attributes accordingly. Alternatively, design with lazy loading in mind and use screen relative units (eg vw, vh, vmin and vmax).

Screen relative units are not possible to be used here - you have no idea how big the image will be on the screen, since you don't know how big the screen is.

Using js onresize event is a no-go, if JS is still needed the spec is worthless. Lazy loading images with JS worked before just fine, this has to be about not needing special JS for this feature.

No, parent is right: It's impossible to satisfy that recommendation, usually.

Screen relative units are not possible to be used here - you have no idea how big the image will be on the screen, since you don't know how big the screen is.

Screen relative units represent a percentage of the screen size (technically speaking it's the viewport really). You don't need to know how big the screen is; you're tell the browser to use, for example, 25% of the viewport height when you set something to be 25vh. If you want 4 images vertically that's really useful. That way the browser knows it needs to put a box 25% of the screen height in the DOM where the image will be loaded later so there's no layout thrashing.

Using js onresize event is a no-go, if JS is still needed the spec is worthless.

The parent suggested they would want to change the width and height attributes of the image when the user resizes their browser. That's exactly what the resize event is for. If you want to display a fixed size image you can use fixed width and height attributes. If you want the image to scale with the viewport size you can either use units that represent a relative size or you need to use JS to modify the attributes. Heck, you can even use media queries to mix and match and have fixed size in some devices and relative in others.

Lazy loading images with JS worked before just fine..

Except you needed JS to do it. With the new HTML spec you get the benefits of basic lazy loading without needing the additional weight of some JS code. That's good.

But you never know that an image should cover 25vh! That depends on the size of the viewport in total, the resolution and the specifics of the layout situation, things like text size. And almost always the width of the viewport decides image width and thus the height of the image.

And that's before resizing anything.

This totally misses the point. I can't run all those calculations while rendering a website. The browser needs to be intelligent enough to not dynamically jump around in the viewport when an element finished loading. Just fix the viewport and attach at the top and bottom.

And relative units don't fix this either as that information still misses the ratio of my image. If it's 100 vw, how high is it? I don't know this information without fetching the image, doing calculations and dynamically updating the DOM with that information.

That sounds like a problem that should be fixed in CSS. Ideally, it should be possible to specify that an image should have a width and/or max-width of 100vw, 100% of its parent, or whatever, taking box-sizing and paddings into account... and then specify that its height should be a certain percentage of its own width. The server already knows the aspect ratio, so it can deliver this information in a 'style' attribute.

I haven't been following the latest developments in CSS for a while, so maybe it's already possible to do this?

I do this in production a few places by setting a div with no content or only absolutely position content to have padding-bottom of the aspect ratio in %. That gets calculated from the width, so if the image is 4:3 my ratio is 75%; 200px wide becomes 150px tall as well. Then, I set the image as a background to the div or absolutely position it inside to fill the space, and it's responsive to the layout while also reserving space for itself.

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