MacOS M1 machines can run iOS applications.
We have an iOS application that runs a fullscreen metal game. The game can also run across all desktop platforms via Steam. In additional to Steam, we would like to make it available through the AppStore on MacOS. We'd like to utilise our iOS builds for this so that the Apple payment (micro-transactions) and sign-in processes can be reused.
While the app runs on MacOS, it runs in a small iPad shaped window that cannot be resized. We do not want to add iPad multitasking support (portrait orientation is not viable), but would like the window on MacOS to be expandable to full screen. Currently there is an option to make it full screen, but the metal view (MTKView) delegate does not receive a drawableSizeWillChange event for this, meaning the new resolution of the window cannot be received.
Is there another method of retrieving a window size change event in this context? What is the recommended way of enabling window resizing on MacOS but not iPad for a single iOS app?
You are not being notified of a size change because there is no size change!
On Macs with M1, iPad apps that do not support iPad multitasking (as well as all iPhone apps) receive a single screen + scene size, which never changes after launch. This is done for compatibility reasons, because iPads and iPhones don't change their physical screen resolution on you, either.
When the window is resized, e.g. by using the Window->Zoom menu item, or by taking the window full screen, your fixed-size UIWindowScene is scaled up or down by macOS automatically, and your app does not find out about this.
And as you point out, iPad multitasking support would cause your window(s) to become resizable, but live-resizing of e.g. game framebuffers is often not feasible.
But I have good news for you!
We've added two new Mac-only Info.plist keys that may provide just what you need:
-
UISupportsTrueScreenSizeOnMacwill give you the true native resolution of the screen where your app was initially launched. This implies that you are prepared to deal with the wide variety of display configurations that you might encounter on a Mac, including 1x and 2x display resolutions, ultrawide and portrait displays, as well as very small or very large sizes. For example, if your content needs to use a specific aspect ratio, it would be up to you to add letterboxing or pillarboxing, as needed. -
UILaunchToFullScreenByDefaultOnMacwill tell the system that your app prefers to enter fullscreen mode as soon as it's launched. However, note that state restoration will override this default behavior.
When you combine both keys, this gives your iPad app a pixel-perfect, edge-to-edge, full screen experience on Macs with M1!
Older versions of macOS (before 12.1) will simply ignore these keys, so you get standard iPad resolutions instead. And they are also ignored on all other platforms.
For more details, you can also check out the WWDC 2022 session, titled "Bring your iOS app to the Mac".
