Apple explains why new Project Catalyst is limited to iPadOS apps

At this year’s WWDC, Apple lifted the lid on Project Catalyst, a new tool that would allow developers to port their iPad apps over to the Mac with little development time or effort.

It’s the biggest step yet in enabling cross-platform apps, potentially unlocking millions of new apps on the Mac, and enabling developers to generate more income from their software.

Whilst the news went down well, some questioned why Apple had limited the new feature to iPad apps, rather than apps on iOS, too.

Ars Technica spoke with some of the team members working on Project Catalyst, who shared more information on their decisions.

Todd Benjamin, Apple’s senior director of marketing for macOS, said: “Design-wise, the difference between an iPad app and an iPhone app is that the iPad app has gone through a design iteration to take advantage of more screen space.

“And as you bring that app over to the Mac… you have something that’s designed around that space that you can work with and that you can start from.”

Ali Ozer, Apple’s engineering manager, added: “This is one way of making developers aware that an iPhone app in its current form might not be the right design.”

Apple has already confirmed that companies such as Twitter and TripIt have ported their iPad apps over to the Mac successfully.

It’s expected that these apps will be available on release of macOS Catalina, alongside Asphalt 9: Legends.

Project Catalyst “just works”

“We realized that we were unable to provide the same level of support to all of the Twitter clients, which ended up hurting some of them, including Twitter for Mac,” Twitter engineer Nolan O’Brien told ArsTechnia.

“What Project Catalyst specifically offers is the ability to use our existing codebase, meaning that we don’t have to maintain separate code or a separate team to support Twitter for Mac,” he added.

“The surprising thing that got us excited about Project Catalyst was how much of our existing iOS codebase was able to just work.”

“Multiple-window support isn’t simple, and it is different than windows with AppKit,” he added.

“Beyond that, multiple windows means each window is running simultaneously and can break expectations on being confined to one presented view controller at a time; they also need to deal with resizing which can run up against assumptions we’ve made when building for an iPad.”

“Not having any events for when the app is backgrounded or minimized” demanded some additional thought and work. “This affects things like database persistence, suspending active operations that don’t need to be running and generally maintaining good hygiene for the app’s lifetime,” O’Brien said.

“One of the challenges we faced was that we had many years of built-up infrastructure and features using OpenGL: blurs, photo filters, graphical touches and flair,” O’Brien said.

“Since OpenGL was deprecated at WWDC last June, we focused this past year on deprecating it on our end as well.”

Are you looking forward to seeing more iPadOS apps coming to the Mac this fall? Which, if any, are you ready to download from the Mac App Store on day one? Let us know on Twitter using @AppleMagazine and check back soon for the latest Apple news and rumors.

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