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Comment by guyzero | Hacker News Reader

Yes, I do understand the issue with the aspect ratio, which is indeed good design, but parent comment's example is that "you can run two apps side by side" is the tautology. Well, at least since the invention of double-entry bookkeeping and getting rid of Archimedian phone design.

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No, you can't, unless the apps are designed for different aspect ratios.

If the outer screen has dimensions X by Y, then you unfold it to have the inner screen with dimensions 2X by Y, which cleanly permits side by side apps at the original dimensions of X by Y. This is true for any ratio between X and Y.

If the user isn't going to be multitasking, then the app needs to additionally support the widescreen dimensions of 2X by Y, and the portrait orientation of Y by 2X. Both of these are so drastically larger overall that aspect ratio is a barely-relevant part of the UI layout problem, because nobody wants every button and text label to be double the size (which would mostly defeat the benefits of having the larger screen for anything other than multitasking).

The inside screen, when divided in two vertically, along the fold line, is exactly the same dimensions as the outer screen. Pretty much by definition. Any folding phone, of any aspect ratio, can run two apps on the interior display side by side.

The issue of the internal screen being the same aspect ratio as the external when rotated is completely separate.

But, the iPhone Duo has a different aspect ratio from a regular iPhone. So your app needs to be designed for multiple aspect ratios anyway.

which they have to be anyway, to support normal iphones and maybe ipads and in many cases a cackle of Android phones too. (but I still think this is brilliant design)

in this thread many people have clearly never developed for iOS

Here's just the screen sizes, not even taking into account actual resolution:

    iPhone (2007)     3.5" 74.0 × 49.3    36 cm²
    iPhone 5          4.0" 88.6 × 49.8    44 cm²
    iPhone 12 mini    5.4" 124.5 × 57.5   72 cm²
    iPhone Duo, cover 5.4" 113.4 × 77.2   88 cm²
    iPhone 6 Plus     5.5" 121.8 × 68.5   83 cm²
    iPhone X          5.8" 133.7 × 61.8   83 cm²
    iPhone Air        6.5" 150.0 × 69.1  104 cm²
    iPhone 18 Pro Max 6.9" 159.2 × 73.3  117 cm²
    iPhone Duo, inner 7.6" 157.6 × 111.5 176 cm²

Now, you can leave out a few of those as hopelessly obsolete like the OG iphone, 5, 12 mini, arguably the x, but it's still a pretty wide selection.

Good list. And if you support both portrait and landscape, you need to support twice that, and you need to be able to switch on the fly.

But for the apps that don't currently support both orientations, it's possible they don't have support for switching aspect ratio on the fly. This design might help with those apps not completely breaking when folding/unfolding.

Yeah to be fair I'm all for the 1/sqrt(2) aspect ratio, I just think it's funny that it's treated as some kind of holy design constraint when they're all over the map on phone sizing :)

And the extra irony is I'm currently shipping an app that doesn't deal well with different size phones (just pads the edges), heh, so do as I say, not as I do.

12 mini and 13 mini remain supported in iOS 27.

The missing piece that makes it not a tautology is that two apps side by side have the same aspect ratio as one app full screen (but 90 degrees rotated)

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