vulkan

Slightly high level Haskell bindings to the Vulkan graphics API.

These bindings present an interface to Vulkan which looks like more idiomatic Haskell and which is much less verbose than the C API. Nevertheless, it retains access to all the functionality. If you find something you can do in the C bindings but not in these high level bindings please raise an issue.

Practically speaking this means:

• No fiddling with vkGetInstanceProcAddr or vkGetDeviceProcAddr to get function pointers, this is done automatically on instance and device creation¹.

• No setting the sType member, this is done automatically.

• No passing length/pointer pairs for arrays, Vector is used instead².

• No passing pointers for return values, this is done for you and multiple results are returned as elements of a tuple.

• No checking VkResult return values for failure, a VulkanException will be thrown if a Vulkan command returns an error VkResult.

• No manual memory management for command parameters or Vulkan structs. You'll still have to manage buffer and image memory yourself however.

Package structure

Types and functions are placed into modules according to the features and extensions portions of the specification. As these sections only mention functions, a best guess has to be made for types. Types and constants are drawn in transitively according to the dependencies of the functions.

It should be sufficient to import Vulkan.CoreXX along with Vulkan.Extensions.{whatever extensions you want}. You might want to import Vulkan.Zero too.

These bindings are intended to be imported qualified and do not feature the Vk prefixes on commands, structures, members or constants.

Things to know

• Documentation is included more or less verbatim from the Vulkan C API documentation. The parameters it references might not map one-to-one with what's in these bindings. It should be obvious in most cases what it's trying to say. If part of the documentation is misleading or unclear with respect to these Haskell bindings please open an issue and we can special case a fix.

  • The haddock documentation can be browsed on Hackage or here

• Parameters are named with the ::: operator where it would be useful; this operator simply ignores the string on the left.

• There exists a Zero type class defined in Vulkan.Zero. This is a class for initializing values with all zero contents and empty arrays. It's very handy when initializing structs to use something like zero { only = _, members = _, i = _, care = _, about = _ }.

• The library is compiled with -XStrict so expect all record members to be strict (and unboxed when they're small)

• Calls to Vulkan are marked as unsafe by default to reduce FFI overhead.

  • This can be changed by setting the safe-foreign-calls flag.
  • It means that Vulkan functions are unable to safely call Haskell code. See the Haskell wiki for more information. This is important to consider if you want to write allocation or debug callbacks in Haskell.
  • It's also means that the garbage collector will not run while these calls are in progress. For some blocking functions (those which can return VK_TIMEOUT and those with wait in the name) a safe version is also provided with the Safe suffix.

• As encouraged by the Vulkan user guide, commands are linked dynamically (with the sole exception of vkGetInstanceProcAddr).

  • The function pointers are attached to any dispatchable handle to save you the trouble of passing them around.
  • The function pointers are retrieved by calling vkGetInstanceProcAddr and vkGetDeviceProcAddr. These are stored in two records InstanceCmds and DeviceCmds which store instance level and device level commands respectively. These tables can be initialized with the initInstanceCmds and initDeviceCmds found in Vulkan.Dynamic.

• There are nice Read and Show instances for the enums and bitmasks. These will, where possible, print and parse the pattern synonyms. For example one can do the following:

  > read @COMPARE_OP "COMPARE_OP_LESS"
  COMPARE_OP_LESS
  

• Make sure that all the functions you're going to use are not nullPtr in InstanceCmds or DeviceCmds before calling them or the command will throw an IOException. The *Cmds records can be found inside any dispatchable handle.

Minor things

• To prevent a name clash between the constructors of VkClearColorValue and VkPerformanceCounterResultKHR the latter have had Counter suffixed.

• To prevent a name clash between the constructors of DeviceOrHostAddressKHR and DeviceOrHostAddressConstKHR the latter have had Const suffixed.

How the C types relate to Haskell types

These bindings take advantage of the meta information present in the specification detailing the validity of structures and arguments.

• Vector is used in place of pointers to arrays with associated length members/parameters. When interfacing with Vulkan these bindings automatically set the length member/parameter properly. If the vector is optional but the length is not then the length member/parameter is preserved, but will be inferred if the vector is present and the length is 0.

• If a struct member or command parameters in the specification is a optional pointer (it may be null) this is replaced with a Maybe value.

• If a struct has a member which can only have one possible value (the most common example is the sType member, then this member is elided.

• C strings become ByteString. This is also the case for fixed length C strings, the library will truncate overly long strings in this case.

• Pointers to void accompanied by a length in bytes become ByteString

• Shader code is represented as ByteString

• VkBool32 becomes Bool

• Some Vulkan commands or structs take several arrays which must be the same length. These are currently exposed as several Vector arguments which must be the same length. If they are not the same length an exception is thrown.

If anything is unclear please raise an issue. The marshaling to and from Haskell and C is automatically generated and I've not checked every single function. It's possible that there are some commands or structs which could be represented better in Haskell, if so please also raise an issue.

Vulkan errors

If a Vulkan command has the VkResult type as a return value, this is checked and a VulkanException is thrown if it is not a success code. If the only success code a command can return is VK_SUCCESS then this is elided from the return type. If a command can return other success codes, for instance VK_EVENT_SET then the success code is exposed.

Bracketing commands

There are certain sets commands which must be called in pairs, for instance the create and destroy commands for using resources. In order to facilitate safe use of these commands, (i.e. ensure that the corresponding destroy command is always called) these bindings expose similarly named commands prefixed with with (for Create/Destroy and Allocate/Free pairs) or use for (Begin/End pairs). If the command is used in command buffer building then it is additionally prefixed with cmd.

These are higher order functions which take as their last argument a consumer for a pair of create and destroy commands. Values which fit this hole include Control.Exception.bracket, Control.Monad.Trans.Resource.allocate and (,).

An example is withInstance which calls createInstance and destroyInstance. Notice how the AllocationCallbacks parameter is automatically passed to the createInstance and destroyInstance command.

createInstance
  :: forall a m
   . (PokeChain a, MonadIO m)
  => InstanceCreateInfo a
  -> Maybe AllocationCallbacks
  -> m Instance

destroyInstance
  :: forall m
   . MonadIO m
  => Instance
  -> Maybe AllocationCallbacks
  -> m ()

withInstance
  :: forall a m r
   . (PokeChain a, MonadIO m)
  => InstanceCreateInfo a
  -> Maybe AllocationCallbacks
  -> (m Instance -> (Instance -> m ()) -> r)
  -> r

Example usage:

import Control.Monad.Trans.Resource (runResourceT, allocate)
-- Create an instance and print its value
main = runResourceT $ do
  (instanceReleaseKey, inst) <- withInstance zero Nothing allocate
  liftIO $ print inst

-- Begin a render pass, draw something and end the render pass
drawTriangle =
  cmdUseRenderPass buffer renderPassBeginInfo SUBPASS_CONTENTS_INLINE bracket_
    $ do
        cmdBindPipeline buffer PIPELINE_BIND_POINT_GRAPHICS graphicsPipeline
        cmdDraw buffer 3 1 0 0

These pairs of commands aren't explicit in the specification, so a list of them is maintained in the generation code, if you see something missing please open an issue (these pairs are generated in VK/Bracket.hs).

Dual use commands

Certain commands, such as vkEnumerateDeviceLayerProperties or vkGetDisplayModePropertiesKHR, have a dual use. If they are not given a pointer to return an array of results then they instead return the total number of possible results, otherwise they return a number of results. There is an idiom in Vulkan which involves calling this function once with a null pointer to get the total number of queryable values, allocating space for querying that many values and they calling the function again to get the values. These bindings expose commands which automatically return all the results. As an example enumeratePhysicalDevices has the type MonadIO m => Instance -> m (Result, Vector PhysicalDevice).

Structure chains

Most structures in Vulkan have a member called pNext which can be a pointer to another Vulkan structure containing additional information. In these high level bindings the head of any struct chain is parameterized over the rest of the items in the chain. This allows for using type inference for getting struct chain return values out of Vulkan, for example: getPhysicalDeviceFeatures2 :: (PokeChain a, PeekChain a) => PhysicalDevice -> IO (PysicalDeviceFeatures2 a); here the variable a :: [Type] represents the structures present in the chain returned from vkGetPhysicalDeviceFeatures2.

There exists a GADT SomeStruct which captures the case of an unknown tail in the struct chain. This is also used for nested chains inside structs.

Struct chains inside records are represented as nested tuples: next :: (Something, (SomethingElse, (AThirdThing, ())))

There are two pattern synonyms exposed in Vulkan.CStruct.Extends which help in constructing and deconstructing struct chains.

• h ::& t which appends the tail t to the struct h
• t :& ts which constructs a struct extending tail comprising struct t and structs ts. Note that you must terminate the list with ().

For example, to create an instance with a debugUtilsMessenger and the validation layer's best practices output enabled:

makeInst = do
  let debugCreateInfo = _ :: DebugUtilsMessengerCreateInfoEXT
      validationFeatures = ValidationFeaturesEXT [VALIDATION_FEATURE_ENABLE_BEST_PRACTICES_EXT] []
      instanceCreateInfo = zero ::& debugCreateInfo :& validationFeatures :& ()
  createInstance instanceCreateInfo Nothing

And to deconstruct a return value with a struct tail, for example to find out if a physical device supports Timeline Semaphores:

hasTimelineSemaphores phys = do
  _ ::& PhysicalDeviceTimelineSemaphoreFeatures hasTimelineSemaphores :& () <-
    getPhysicalDeviceFeatures2 phys
  pure hasTimelineSemaphores

Building

This package requires GHC 8.6 or higher due to the use of the QuantifiedConstraints language extension.

Make sure you have initialized the VulkanMemoryAllocator submodule if you intend to build the VulkanMemoryAllocator package.

If you provision libvulkan.so (the Vulkan loader) with nix and you're not on NixOS, you'll have to use NixGL to run your programs. For this reason it's recommended to use the system-provided libvulkan.so.

For instructions on how to regenerate the bindings see the readme in ./generate-new.

To build the example programs. You'll need to supply the following system packages:

• vulkan-loader (for libvulkan.so)
• vulkan-headers (for vulkan.h)
• pkg-config and SDL2 to build the Haskell sdl2 package.
• glslang (for the glslangValidator binary, to build the shaders)

Examples

There exists a package to build some example programs in the examples directory.

Current Status

All the core Vulkan 1.0, 1.1, and 1.2 functionality is here as well as all the extensions.

This is currently a 64 bit only library.

See also

The VulkanMemoryAllocator package (source in the VulkanMemoryAllocator directory) has similarly styled bindings to the Vulkan Memory Allocator library.

The vulkan-utils package (not currently on Hackage) includes a few utilities for writing programs using these bindings.

For an alternative take on Haskell bindings to Vulkan see the vulkan-api package. vulkan-api stores Vulkan structs in their C representation as ByteArray# whereas this library allocates structs on the stack and keeps them alive for just the lifetime of any Vulkan command call.

---

1: Note that you'll still have to request any required extensions for the function pointers belonging to that extension to be populated. An exception will be thrown if you try to call a function pointer which is null.

2: The exception is where the spec allows the application to pass NULL for the vector with a non-zero count. In these cases it was deemed clearer to preserve the "count" member and allow the Haskell application to pass a zero-length vector to indicate NULL.