Can Game Mode be activated when a child (Java) process's window is fullscreened?

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Created 6d

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Imagine a native macOS app that acts as a "launcher" for a Java game.** For example, the "launcher" app might use the Swift Process API or a similar method to run the java command line tool (lets assume the user has installed Java themselves) to run the game.

I have seen How to Enable Game Mode. If the native launcher app's Info.plist has the following keys set:

LSApplicationCategoryType set to public.app-category.games
LSSupportsGameMode set to true (for macOS 26+)
GCSupportsGameMode set to true

The launcher itself can cause Game Mode to activate if the launcher is fullscreened. However, if the launcher opens a Java process that opens a window, then the Java window is fullscreened, Game Mode doesn't seem to activate. In this case activating Game Mode for the launcher itself is unnecessary, but you'd expect Game Mode to activate when the actual game in the Java window is fullscreened.

Is there a way to get Game Mode to activate in the latter case?

** The concrete case I'm thinking of is a third-party Minecraft Java Edition launcher, but the issue can also be demonstrated in a sample project (FB13786152). It seems like the official Minecraft launcher is able to do this, though it's not clear how. (Is its bundle identifier hardcoded in the OS to allow for this? Changing a sample app's bundle identifier to be the same as the official Minecraft launcher gets the behavior I want, but obviously this is not a practical solution.)

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Answer 1

DTS Engineer OP

Apple

6d

Hello,

I'm uncertain how to speak to CLI tools and Java games launched from a macOS app. These sound like security and sandboxing questions which we recommend you ask about in those sections of the forums.

For games, I've heard of architectures where a parent app launches mini-games built with a 3rd-party game engine. So that at least is possible.

In this case it sounds like the launcher app creates a new window via Java and this seems unlikely to work i.e. Game Mode won't migrate to the new window.

Game Mode is fully supported for conventional full-screen games such as those you'd build with Metal or RealityKit.

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Answer 2

kthchew OP

5d

Thanks for that. I asked over in the privacy/security section of the forums and the verdict seems to be that these types of properties don't get inherited because that's not how it works. However I was given the suggestion to possibly change the Java executable's Info.plist instead, although trying this didn't seem to successfully get Game Mode to activate (tested on macOS 15.5 (24F74)), unfortunately. (Is that expected behavior?)

So looks like this won't work, as you thought.

Though it is strange that Game Mode does work with apps like the Minecraft official launcher which use this architecture, which seems to imply there is some way this is done. I can't find a code-level way to implement this, but I do see that:

If the "launcher" app is opened from Steam and then the launcher app opens the Java game, then fullscreening the Java game does activate Game Mode. So seems like children of Steam have some kind of special handling, though I'm not sure if that's the doing of Steam or the OS.
If you change an app's bundle ID to that of the Minecraft launcher (com.mojang.minecraftlauncher) it also causes Game Mode to enable when the Java window is fullscreened. Since the code in a sample app I'm using to test this doesn't change, only the bundle identifier, it seems like this is done at the OS level. Although obviously pretending to be the official Minecraft launcher is not a possible solution in the real app.

It seems like the system has special handling for at least the second case somehow since the behavior only changes based on the bundle identifier of the app. Is this type of behavior (inheriting the Game Mode support for the child process) accessible to other developers?

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