Supporting Catalyst's Optimize for Mac with Manual Layout

May 16 2021

"Optimize Interface for Mac checkbox"

A key part of supporting Catalyst's new Mac Idiom (Optimize Interface for Mac) is having a way to ensure that every hardcoded number you use for layout has a value both for iOS, and for macOS, which no longer uses an automatic 0.77 scale and now lets you address every pixel on the display.

There are plenty of strategies to come at this problem, but the one I've settled on (and which I find very easy to use) is an extension to CGFloat called 'UIFloat'.

Now, whenever I'm defining a value that's going to be used on screen, either for layout frames, margins, or text sizes, I make sure to wrap it in a UIFloat() and then just continue to design my layout using the same metrics I'm using for iOS, using UIFloat anywhere that accepts a CGFloat. This can be used in UIKit or SwiftUI code.

let margin = UIFloat(20)

As a result, your Mac Catalyst app won't require you to completely redo your layouts with alternate metrics, and you can continue to design just one interface that works great on both iOS and macOS.

This also makes back-deploying to macOS Catalina a breeze, as you can ship a dual-mode Catalyst app that uses both the original Scaled mode for macOS 10.15 and the Optimized mode for macOS 11 using this little non-obvious Xcode settings trick.

This has become the first piece of code I add to all new projects over the past year, and I find it invaluable. I kinda wish it were built in to the SDK, so that we always define our UIs in terms of UI points and not CGFloats. Hopefully you might find it useful too.

import UIKit

public let supportsMacIdiom = !(UIDevice.current.userInterfaceIdiom == .pad)

@inlinable func UIFloat(_ value: CGFloat) -> CGFloat
    #if targetEnvironment(macCatalyst)
    return round((value == 0.5) ? 0.5 : value * (supportsMacIdiom ? 0.77 : 1.0))
    return value