qt: add Vulkan/molten-vk support

[loganmc10]

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Hi, I'm hoping to resurrect #50038, I'm not sure why it wasn't merged. See also https://www.qt.io/blog/2018/05/30/vulkan-for-qt-on-macos

I am the developer of simple64 (https://simple64.github.io), an N64 emulator. I'd like to add Mac OS support, and this is blocking me

[loganmc10]

@carlocab I see that you've been handling recent Qt commits

[SMillerDev]

Please don't tag individual maintainers, no pull request is not important enough to demand volunteer time like that.

[carlocab]

I don't have the time to review this properly, but a few comments:

1. Commit message needs fixing. (See guide in PR template or summary below.)
2. This dependency needs to be macOS-only, since MoltenVK is not available on Linux.
3. MoltenVK is a pretty heavy dependency to add for something that appears pretty niche.

Re commit style:

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[loganmc10]

Commit message needs fixing. (See guide in PR template or summary below.)

Done

This dependency needs to be macOS-only, since MoltenVK is not available on Linux.

Done

MoltenVK is a pretty heavy dependency to add for something that appears pretty niche.

Qt is primarily used for GUI applications, and with OpenGL deprecated on Mac OS, it's really the only good option for GPU accelerated applications. If you install Qt on a Linux distro, or Windows, it's going to come with Vulkan support, so excluding it on brew causes a significant difference in features vs Linux or Windows.

[carlocab]

Thoughts here, @paperchalice, @jonaski?

[carlocab]

excluding it on brew causes a significant difference in features vs Linux or Windows.

This doesn't really bother me -- having fewer features than on Linux is pretty typical for macOS. To me, it's really a matter of whether there will be a significant fraction of users of this formula who would find this useful.

[paperchalice]

qt with vulkan support in fact doesn't contain the molten-vk linkage, so mark it as build dependency and introduce build dependency vulkan-headers is enough, and the extra cmake flags are unnecessary here. For test, we need vulkan-loader, vulkan-headers and a vulkan implementation. BTW there is an upstream issue about it on macOS.

[carlocab]

qt with vulkan support in fact doesn't contain the molten-vk linkage, so mark it as build dependency and introduce build dependency vulkan-headers is enough, and the extra cmake flags are unnecessary here. For test, we need vulkan-loader, vulkan-headers and a vulkan implementation. BTW there is an upstream issue about it on macOS.

If it's a build-only dependency then I'm fine with this. We do need a test, though; thanks for laying out a starting point.

[loganmc10]

Full disclosure: I don't have a Mac or any way to test this, so I'm fine with whatever solution as long as Vulkan support is added to Qt, I'd like to be able to provide a Mac build of the emulator

[loganmc10]

ok PR has been updated per @paperchalice suggestions

[carlocab]

Full disclosure: I don't have a Mac or any way to test this, so I'm fine with whatever solution as long as Vulkan support is added to Qt, I'd like to be able to provide a Mac build of the emulator

Does this mean you haven't been able to test whether changing our Qt build in this way works for your changes at simple64/simple64#316?

If we add a test for Vulkan support I can cherry-pick this onto #110816 and get a build going.

[loganmc10]

Does this mean you haven't been able to test whether changing our Qt build in this way works for your changes at simple64/simple64#316?

Correct, simple64 used to support Mac, another developer worked on the support, but it stopped working when we migrated from OpenGL to Vulkan. I'm trying to get a DMG again so that someone can test it and get it working if anything needs to be done.

[carlocab]

Ok, given that we don't even know if this change works for anybody, I'm going to insist that we have a test for this functionality. You may need to find a Mac to build and test on -- GitHub runners will not suffice (the time to build Qt exceeds their 6 hour time limit).

Or, perhaps @paperchalice might be interested in picking this up.

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[carlocab]

I don't think there's going to be any progress here, so I'm closing this.

If you'd still like to pursue this change, please feel free to open a new pull request. However, if you choose to do so: please test that your changes produce the intended result, and update the formula's test to include a minimal check for the usability of the new features.