Add VK_KHR_timeline_semaphore extension support

[zedrian]

Introduced ash::extensions::khr::TimelineSemaphore structure written by analogy with khr::Swapchain (except the fact that it does not hold any special functions besides those ones that are needed for extension loading).

Enabling timeline semaphore support in the application now:

let device_extension_names = [
    ash::extensions::khr::TimelineSemaphore::name().as_ptr(),
    // other device extensions
];

let mut timeline_semaphore_features = vk::PhysicalDeviceTimelineSemaphoreFeatures::builder()
    .timeline_semaphore(true);

let device_create_info = vk::DeviceCreateInfo::builder()
    .enabled_extension_names(&device_extension_names)
    .push_next(&mut timeline_semaphore_features)
    // other settings
    .build();
let device = unsafe { instance.create_device(physical_device, &device_create_info, None)? };

[zedrian]

@farnoy I guess this PR may be interesting for you because you already requested this extension in #178 ☺

[farnoy]

Is this useful? KhrTimelineSemaphoreFn does not have any interesting functions itself.

The things that are of particular interest are (right now at least) defined on DeviceFnV1_2, like get_semaphore_counter_value. I believe these should be provided by your ash::extensions::TimelineSemaphore to be useful.

Either way, thank you for the effort, I just used the 1.2 versions myself.

[zedrian]

@farnoy I tested on my side, functions related to timeline semaphores defined in DeviceFnV1_2 become available just using ash::device::Device, e.g.

unsafe { device.wait_semaphores(device.handle(), &semaphore_wait_info, std::u64::MAX).unwrap(); }

so you don't have to grab function pointers by yourself anymore.

[farnoy]

Have you tested on a 1.0/1.1 application with this? I don't think that would work since the functions have a KHR suffix there. So using a DeviceFnV1_2.get_semaphore_counter_value would not work because it would try to load a vkGetSemaphoreCounterValue, whereas this extension should load vkGetSemaphoreCounterValueKHR.

[zedrian]

@farnoy I tried this on API 1.1, and it doesn't work. As I understand, that happens because of VK_KHR_timeline_semaphore appeared in Vulkan 1.2.
Is this a problem?

[zedrian]

@farnoy I misread your comment at first, sorry. Yes, it will not work because of the KHR suffix in older versions of Vulkan.

[Ralith]

The point is, the extension should provide access to the KHR-suffixed versions, and therefore be usable on 1.1 impls.

[zedrian]

So expected implementation is that Vulkan 1.2 users call functions like

device.wait_semaphores(device.handle(), &semaphore_wait_info, timeout)?;

and Vulkan 1.1 users call functions like

timeline_semaphore_loader.wait_semaphores(&semaphore_wait_info, timeout)?;

right?

[farnoy]

I would summarize it as:

1.2 users don't use this and call device.wait_semaphores(device.handle(), &semaphore_wait_info, timeout)?;

1.0/1.1 users need to enable the device extension and call timeline_semaphore_loader.wait_semaphores_khr(device.handle(), &semaphore_wait_info, timeout)?;

I think the suffix is usually preserved in ash, and the interface should be the same (because it is the same in the spec between the extension and 1.2 core)

[zedrian]

BTW, VK_KHR_timeline_semaphore extension additionally requires VK_KHR_get_physical_device_properties2. But as I can see from my tests, it's enough to just add that extension name to the list of enabled extensions.

[zedrian]

I added the *_khr functions to the TimelineSemaphore as discussed, so the following code is available now for Vulkan 1.0/1.1 users:

timeline_semaphore_loader.get_semaphore_counter_value_khr(device.handle(), semaphore)?;

timeline_semaphore_loader.wait_semaphores_khr(device.handle(), &semaphore_wait_info, timeout)?;
timeline_semaphore_loader.signal_semaphore_khr(device.handle(), &semaphore_signal_info, timeout)?;

[farnoy]

LGTM

[MaikKlein]

Hey thanks for the PR. Sorry for not responding sooner. I made a PR to include function aliases in extensions #279

pub struct KhrTimelineSemaphoreFn {
    pub get_semaphore_counter_value:
        extern "system" fn(device: Device, semaphore: Semaphore, p_value: *mut u64) -> Result,
    pub wait_semaphores: extern "system" fn(
        device: Device,
        p_wait_info: *const SemaphoreWaitInfo,
        timeout: u64,
    ) -> Result,
    pub signal_semaphore:
        extern "system" fn(device: Device, p_signal_info: *const SemaphoreSignalInfo) -> Result,
}

No need to fetch those function pointers yourself and we should update this PR when this is merged in.

[zedrian]

That would be great! Waiting for #279.

[MaikKlein]

Looks good! LGTM