Dispatch mechanism

Some API functions cannot be called directly from the Vulkan library. In particular, extension functions must be called through a pointer obtained via API commands. In addition, most functions can be made faster by calling directly into their function pointer, instead of going through the loader trampoline which resolves the function pointer every time.

To circumvent that, we provide a handy way for retrieving and calling into function pointers, as well as a thread-safe global dispatch table that can automate this work for you.

Retrieving function pointers

API Function pointers can be obtained with the function_pointer function, using the API function name.

using Vulkan

const instance = Instance([], [])
const pdevice = first(unwrap(enumerate_physical_devices(instance)))
const device = Device(pdevice, [DeviceQueueCreateInfo(0, [1.0])], [], [])
Device(Ptr{Nothing} @0x0000000003e7e318)
julia> function_pointer("vkCreateInstance")Ptr{Nothing} @0x00007f818fef61b0
julia> function_pointer(instance, "vkDestroyInstance")Ptr{Nothing} @0x00007f818fef8e10
julia> function_pointer(device, "vkCreateFence")Ptr{Nothing} @0x00007f81769143fb

It is essentially a wrapper around get_instance_proc_addr and get_device_proc_addr, leveraging multiple dispatch to make it more intuitive to use.

Providing function pointers

Every wrapper function or handle constructor has a signature which accepts the standard function arguments plus a function pointer to call into. For example, instead of doing

foreach(println, unwrap(enumerate_instance_layer_properties()))

you can do

fptr = function_pointer("vkEnumerateInstanceLayerProperties")
foreach(println, unwrap(enumerate_instance_layer_properties(fptr)))

In the case of a handle constructor which calls both a creation and a destruction function, there is an argument for each corresponding function pointer:

fptr_create = function_pointer(device, "vkCreateFence")
fptr_destroy = function_pointer(device, "vkDestroyFence")
Fence(device, fptr_create, fptr_destroy)
Fence(Ptr{Nothing} @0x0000000006fff598)

Automatic dispatch

Querying and retrieving function pointers every time results in a lot of boilerplate code. To remedy this, we provide a concurrent global dispatch table which loads all available function pointers for loader, instance and device commands. It has one dispatch table per instance and per device to support using multiple instances and devices at the same time.

This feature can be disabled by setting the preference USE_DISPATCH_TABLE to "false".

Warn

All instance and device creations must be externally synchronized if the dispatch table is enabled. This is because all function pointers are retrieved and stored right after the creation of an instance or device handle.


This page was generated using Literate.jl.