Add support for Vulkan Events if available

[billhollings]

The latest version of Metal now supports some form of behaviour similar to Vulkan Events.

[iOS4all]

@billhollings please can we add vulkan to ppsspp to could select it as a backend?
Of course I mean iOS devices.
So if there’s any cydia source to could install MoltenVK it’ll be great

[billhollings]

@iOS4all

Is this related to Vulkan Events? It sounds like this should be posted as a separate enhancement topic.

We definitely encourage the PPSSPP team integrate MoltenVK into their Vulkan implementation for iOS and macOS...and we would be happy to provide assistance.

[mbarriault]

It looks like events might be able to implemented with a combination of MTLSharedEvent (for CPU triggering) and MTLEvent (for stage synchronization).

[kristofferR]

The lack of Vulkan Events support in MoltenVK is currently blocking DXVK support:
doitsujin/dxvk#1077 (comment)

[billhollings]

SIGGRAPH generated some good feedback regarding interest in this feature.

I'll start working on this feature this week. If anyone has started work on this already...or has design ideas...please let me know.

@cdavis5e

[cdavis5e]

I haven't started on this.

I have, however, looked at gfx-rs's implementation. They're just delaying command buffer submission, similar to what we do with VkSemaphore. We could probably have that as a fallback in case MTLSharedEvent isn't supported.

[billhollings]

Support added in PR #708.

[ovvldc]

So this can now be removed from the list of Known Limitations in https://github.com/KhronosGroup/MoltenVK/blob/master/Docs/MoltenVK_Runtime_UserGuide.md#limitations ?

That list its getting impressively short, by the way.

[billhollings]

So this can now be removed from the list of Known Limitations

Oops! Good catch! I'll update the doc.