Vulkan® 1.3.252 - A Specification

4. Initialization

Before using Vulkan, an application must initialize it by loading the Vulkan commands, and creating a VkInstance object.

4.1. Command Function Pointers

Vulkan commands are not necessarily exposed by static linking on a platform. Commands to query function pointers for Vulkan commands are described below.

Note

When extensions are promoted or otherwise incorporated into another extension or Vulkan core version, command aliases may be included. Whilst the behavior of each command alias is identical, the behavior of retrieving each alias’s function pointer is not. A function pointer for a given alias can only be retrieved if the extension or version that introduced that alias is supported and enabled, irrespective of whether any other alias is available.

Function pointers for all Vulkan commands can be obtained with the command:

// Provided by VK_VERSION_1_0
PFN_vkVoidFunction vkGetInstanceProcAddr(
    VkInstance                                  instance,
    const char*                                 pName);

instance is the instance that the function pointer will be compatible with, or NULL for commands not dependent on any instance.
pName is the name of the command to obtain.

vkGetInstanceProcAddr itself is obtained in a platform- and loader- specific manner. Typically, the loader library will export this command as a function symbol, so applications can link against the loader library, or load it dynamically and look up the symbol using platform-specific APIs.

The table below defines the various use cases for vkGetInstanceProcAddr and expected return value (“fp” is “function pointer”) for each case. A valid returned function pointer (“fp”) must not be NULL.

The returned function pointer is of type PFN_vkVoidFunction, and must be cast to the type of the command being queried before use.

Table 1. `vkGetInstanceProcAddr` behavior
`instance`	`pName`	return value
*¹	`NULL`	undefined
invalid non-`NULL` instance	*¹	undefined
`NULL`	global command²	fp
`NULL`	vkGetInstanceProcAddr	fp⁵
instance	vkGetInstanceProcAddr	fp
instance	core dispatchable command	fp³
instance	enabled instance extension dispatchable command for `instance`	fp³
instance	available device extension⁴ dispatchable command for `instance`	fp³
any other case, not covered above		`NULL`

1: "*" means any representable value for the parameter (including valid values, invalid values, and NULL).
2: The global commands are: vkEnumerateInstanceVersion, vkEnumerateInstanceExtensionProperties, vkEnumerateInstanceLayerProperties, and vkCreateInstance. Dispatchable commands are all other commands which are not global.
3: The returned function pointer must only be called with a dispatchable object (the first parameter) that is instance or a child of instance, e.g. VkInstance, VkPhysicalDevice, VkDevice, VkQueue, or VkCommandBuffer.
4: An “available device extension” is a device extension supported by any physical device enumerated by instance.
5: Starting with Vulkan 1.2, vkGetInstanceProcAddr can resolve itself with a NULL instance pointer.

Valid Usage (Implicit)

VUID-vkGetInstanceProcAddr-instance-parameter
If instance is not NULL, instance must be a valid VkInstance handle
VUID-vkGetInstanceProcAddr-pName-parameter
pName must be a null-terminated UTF-8 string

In order to support systems with multiple Vulkan implementations, the function pointers returned by vkGetInstanceProcAddr may point to dispatch code that calls a different real implementation for different VkDevice objects or their child objects. The overhead of the internal dispatch for VkDevice objects can be avoided by obtaining device-specific function pointers for any commands that use a device or device-child object as their dispatchable object. Such function pointers can be obtained with the command:

// Provided by VK_VERSION_1_0
PFN_vkVoidFunction vkGetDeviceProcAddr(
    VkDevice                                    device,
    const char*                                 pName);

The table below defines the various use cases for vkGetDeviceProcAddr and expected return value (“fp” is “function pointer”) for each case. A valid returned function pointer (“fp”) must not be NULL.

The returned function pointer is of type PFN_vkVoidFunction, and must be cast to the type of the command being queried before use. The function pointer must only be called with a dispatchable object (the first parameter) that is device or a child of device.

Table 2. `vkGetDeviceProcAddr` behavior
`device`	`pName`	return value
`NULL`	*¹	undefined
invalid device	*¹	undefined
device	`NULL`	undefined
device	requested core version² device-level dispatchable command³	fp⁴
device	enabled extension device-level dispatchable command³	fp⁴
any other case, not covered above		`NULL`

1: "*" means any representable value for the parameter (including valid values, invalid values, and NULL).
2: Device-level commands which are part of the core version specified by VkApplicationInfo::apiVersion when creating the instance will always return a valid function pointer. Core commands beyond that version which are supported by the implementation may either return NULL or a function pointer, though the function pointer must not be called.
3: In this function, device-level excludes all physical-device-level commands.
4: The returned function pointer must only be called with a dispatchable object (the first parameter) that is device or a child of device e.g. VkDevice, VkQueue, or VkCommandBuffer.

Valid Usage (Implicit)

VUID-vkGetDeviceProcAddr-device-parameter
device must be a valid VkDevice handle
VUID-vkGetDeviceProcAddr-pName-parameter
pName must be a null-terminated UTF-8 string

The definition of PFN_vkVoidFunction is:

// Provided by VK_VERSION_1_0
typedef void (VKAPI_PTR *PFN_vkVoidFunction)(void);

This type is returned from command function pointer queries, and must be cast to an actual command function pointer before use.

4.1.1. Extending Physical Device Core Functionality

New core physical-device-level functionality can be used when the physical-device version is greater than or equal to the version of Vulkan that added the new functionality. The Vulkan version supported by a physical device can be obtained by calling vkGetPhysicalDeviceProperties.

4.1.2. Extending Physical Device From Device Extensions

When the VK_KHR_get_physical_device_properties2 extension is enabled, or when both the instance and the physical-device versions are at least 1.1, physical-device-level functionality of a device extension can be used with a physical device if the corresponding extension is enumerated by vkEnumerateDeviceExtensionProperties for that physical device, even before a logical device has been created.

To obtain a function pointer for a physical-device-level command from a device extension, an application can use vkGetInstanceProcAddr. This function pointer may point to dispatch code, which calls a different real implementation for different VkPhysicalDevice objects. Applications must not use a VkPhysicalDevice in any command added by an extension or core version that is not supported by that physical device.

Device extensions may define structures that can be added to the pNext chain of physical-device-level commands.

4.2. Instances

There is no global state in Vulkan and all per-application state is stored in a VkInstance object. Creating a VkInstance object initializes the Vulkan library and allows the application to pass information about itself to the implementation.

Instances are represented by VkInstance handles:

// Provided by VK_VERSION_1_0
VK_DEFINE_HANDLE(VkInstance)

To query the version of instance-level functionality supported by the implementation, call:

// Provided by VK_VERSION_1_1
VkResult vkEnumerateInstanceVersion(
    uint32_t*                                   pApiVersion);

pApiVersion is a pointer to a uint32_t, which is the version of Vulkan supported by instance-level functionality, encoded as described in Version Numbers.

Note

The intended behaviour of vkEnumerateInstanceVersion is that an implementation should not need to perform memory allocations and should unconditionally return VK_SUCCESS. The loader, and any enabled layers, may return VK_ERROR_OUT_OF_HOST_MEMORY in the case of a failed memory allocation.

Valid Usage (Implicit)

VUID-vkEnumerateInstanceVersion-pApiVersion-parameter
pApiVersion must be a valid pointer to a uint32_t value

Return Codes

Success

VK_SUCCESS

Failure

VK_ERROR_OUT_OF_HOST_MEMORY

To create an instance object, call:

// Provided by VK_VERSION_1_0
VkResult vkCreateInstance(
    const VkInstanceCreateInfo*                 pCreateInfo,
    const VkAllocationCallbacks*                pAllocator,
    VkInstance*                                 pInstance);

pCreateInfo is a pointer to a VkInstanceCreateInfo structure controlling creation of the instance.
pAllocator controls host memory allocation as described in the Memory Allocation chapter.
pInstance points a VkInstance handle in which the resulting instance is returned.

vkCreateInstance verifies that the requested layers exist. If not, vkCreateInstance will return VK_ERROR_LAYER_NOT_PRESENT. Next vkCreateInstance verifies that the requested extensions are supported (e.g. in the implementation or in any enabled instance layer) and if any requested extension is not supported, vkCreateInstance must return VK_ERROR_EXTENSION_NOT_PRESENT. After verifying and enabling the instance layers and extensions the VkInstance object is created and returned to the application. If a requested extension is only supported by a layer, both the layer and the extension need to be specified at vkCreateInstance time for the creation to succeed.

Valid Usage

VUID-vkCreateInstance-ppEnabledExtensionNames-01388
All required extensions for each extension in the VkInstanceCreateInfo::ppEnabledExtensionNames list must also be present in that list

Valid Usage (Implicit)

VUID-vkCreateInstance-pCreateInfo-parameter
pCreateInfo must be a valid pointer to a valid VkInstanceCreateInfo structure
VUID-vkCreateInstance-pAllocator-parameter
If pAllocator is not NULL, pAllocator must be a valid pointer to a valid VkAllocationCallbacks structure
VUID-vkCreateInstance-pInstance-parameter
pInstance must be a valid pointer to a VkInstance handle

Return Codes

Success

VK_SUCCESS

Failure

VK_ERROR_OUT_OF_HOST_MEMORY
VK_ERROR_OUT_OF_DEVICE_MEMORY
VK_ERROR_INITIALIZATION_FAILED
VK_ERROR_LAYER_NOT_PRESENT
VK_ERROR_EXTENSION_NOT_PRESENT
VK_ERROR_INCOMPATIBLE_DRIVER

The VkInstanceCreateInfo structure is defined as:

// Provided by VK_VERSION_1_0
typedef struct VkInstanceCreateInfo {
    VkStructureType             sType;
    const void*                 pNext;
    VkInstanceCreateFlags       flags;
    const VkApplicationInfo*    pApplicationInfo;
    uint32_t                    enabledLayerCount;
    const char* const*          ppEnabledLayerNames;
    uint32_t                    enabledExtensionCount;
    const char* const*          ppEnabledExtensionNames;
} VkInstanceCreateInfo;

sType is the type of this structure.
pNext is NULL or a pointer to a structure extending this structure.
flags is a bitmask of VkInstanceCreateFlagBits indicating the behavior of the instance.
pApplicationInfo is NULL or a pointer to a VkApplicationInfo structure. If not NULL, this information helps implementations recognize behavior inherent to classes of applications. VkApplicationInfo is defined in detail below.
enabledLayerCount is the number of global layers to enable.
ppEnabledLayerNames is a pointer to an array of enabledLayerCount null-terminated UTF-8 strings containing the names of layers to enable for the created instance. The layers are loaded in the order they are listed in this array, with the first array element being the closest to the application, and the last array element being the closest to the driver. See the Layers section for further details.
enabledExtensionCount is the number of global extensions to enable.
ppEnabledExtensionNames is a pointer to an array of enabledExtensionCount null-terminated UTF-8 strings containing the names of extensions to enable.

Valid Usage (Implicit)

VUID-VkInstanceCreateInfo-sType-sType
sType must be VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO
VUID-VkInstanceCreateInfo-pNext-pNext
pNext must be NULL
VUID-VkInstanceCreateInfo-flags-zerobitmask
flags must be 0
VUID-VkInstanceCreateInfo-pApplicationInfo-parameter
If pApplicationInfo is not NULL, pApplicationInfo must be a valid pointer to a valid VkApplicationInfo structure
VUID-VkInstanceCreateInfo-ppEnabledLayerNames-parameter
If enabledLayerCount is not 0, ppEnabledLayerNames must be a valid pointer to an array of enabledLayerCount null-terminated UTF-8 strings
VUID-VkInstanceCreateInfo-ppEnabledExtensionNames-parameter
If enabledExtensionCount is not 0, ppEnabledExtensionNames must be a valid pointer to an array of enabledExtensionCount null-terminated UTF-8 strings

// Provided by VK_VERSION_1_0
typedef enum VkInstanceCreateFlagBits {
} VkInstanceCreateFlagBits;

Note

All bits for this type are defined by extensions, and none of those extensions are enabled in this build of the specification.

// Provided by VK_VERSION_1_0
typedef VkFlags VkInstanceCreateFlags;

VkInstanceCreateFlags is a bitmask type for setting a mask, but is currently reserved for future use.

The VkApplicationInfo structure is defined as:

// Provided by VK_VERSION_1_0
typedef struct VkApplicationInfo {
    VkStructureType    sType;
    const void*        pNext;
    const char*        pApplicationName;
    uint32_t           applicationVersion;
    const char*        pEngineName;
    uint32_t           engineVersion;
    uint32_t           apiVersion;
} VkApplicationInfo;

sType is the type of this structure.
pNext is NULL or a pointer to a structure extending this structure.
pApplicationName is NULL or is a pointer to a null-terminated UTF-8 string containing the name of the application.
applicationVersion is an unsigned integer variable containing the developer-supplied version number of the application.
pEngineName is NULL or is a pointer to a null-terminated UTF-8 string containing the name of the engine (if any) used to create the application.
engineVersion is an unsigned integer variable containing the developer-supplied version number of the engine used to create the application.
apiVersion must be the highest version of Vulkan that the application is designed to use, encoded as described in Version Numbers. The patch version number specified in apiVersion is ignored when creating an instance object. The variant version of the instance must match that requested in apiVersion.

Vulkan 1.0 implementations were required to return VK_ERROR_INCOMPATIBLE_DRIVER if apiVersion was larger than 1.0. Implementations that support Vulkan 1.1 or later must not return VK_ERROR_INCOMPATIBLE_DRIVER for any value of apiVersion .

Note

Because Vulkan 1.0 implementations may fail with VK_ERROR_INCOMPATIBLE_DRIVER, applications should determine the version of Vulkan available before calling vkCreateInstance. If the vkGetInstanceProcAddr returns NULL for vkEnumerateInstanceVersion, it is a Vulkan 1.0 implementation. Otherwise, the application can call vkEnumerateInstanceVersion to determine the version of Vulkan.

As long as the instance supports at least Vulkan 1.1, an application can use different versions of Vulkan with an instance than it does with a device or physical device.

Note

The Khronos validation layers will treat apiVersion as the highest API version the application targets, and will validate API usage against the minimum of that version and the implementation version (instance or device, depending on context). If an application tries to use functionality from a greater version than this, a validation error will be triggered.

For example, if the instance supports Vulkan 1.1 and three physical devices support Vulkan 1.0, Vulkan 1.1, and Vulkan 1.2, respectively, and if the application sets apiVersion to 1.2, the application can use the following versions of Vulkan:

Vulkan 1.0 can be used with the instance and with all physical devices.
Vulkan 1.1 can be used with the instance and with the physical devices that support Vulkan 1.1 and Vulkan 1.2.
Vulkan 1.2 can be used with the physical device that supports Vulkan 1.2.

If we modify the above example so that the application sets apiVersion to 1.1, then the application must not use Vulkan 1.2 functionality on the physical device that supports Vulkan 1.2.

Note

Providing a NULL VkInstanceCreateInfo::pApplicationInfo or providing an apiVersion of 0 is equivalent to providing an apiVersion of VK_MAKE_API_VERSION(0,1,0,0).

Valid Usage

VUID-VkApplicationInfo-apiVersion-04010
If apiVersion is not 0, then it must be greater than or equal to VK_API_VERSION_1_0

Valid Usage (Implicit)

VUID-VkApplicationInfo-sType-sType
sType must be VK_STRUCTURE_TYPE_APPLICATION_INFO
VUID-VkApplicationInfo-pNext-pNext
pNext must be NULL
VUID-VkApplicationInfo-pApplicationName-parameter
If pApplicationName is not NULL, pApplicationName must be a null-terminated UTF-8 string
VUID-VkApplicationInfo-pEngineName-parameter
If pEngineName is not NULL, pEngineName must be a null-terminated UTF-8 string

To destroy an instance, call:

// Provided by VK_VERSION_1_0
void vkDestroyInstance(
    VkInstance                                  instance,
    const VkAllocationCallbacks*                pAllocator);

instance is the handle of the instance to destroy.
pAllocator controls host memory allocation as described in the Memory Allocation chapter.

Valid Usage

VUID-vkDestroyInstance-instance-00629
All child objects created using instance must have been destroyed prior to destroying instance
VUID-vkDestroyInstance-instance-00630
If VkAllocationCallbacks were provided when instance was created, a compatible set of callbacks must be provided here
VUID-vkDestroyInstance-instance-00631
If no VkAllocationCallbacks were provided when instance was created, pAllocator must be NULL

Valid Usage (Implicit)

VUID-vkDestroyInstance-instance-parameter
If instance is not NULL, instance must be a valid VkInstance handle
VUID-vkDestroyInstance-pAllocator-parameter
If pAllocator is not NULL, pAllocator must be a valid pointer to a valid VkAllocationCallbacks structure

Host Synchronization

Host access to instance must be externally synchronized
Host access to all VkPhysicalDevice objects enumerated from instance must be externally synchronized