3. Initialization

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

3.1. 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.

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

vkGetInstanceProcAddr

fp4

NULL

vkEnumerateInstanceVersion

fp

NULL

vkEnumerateInstanceExtensionProperties

fp

NULL

vkEnumerateInstanceLayerProperties

fp

NULL

vkCreateInstance

fp

instance

core Vulkan command

fp2

instance

enabled instance extension commands for instance

fp2

instance

available device extension3 commands for instance

fp2

any other case, not covered above

NULL
1

"*" means any representable value for the parameter (including valid values, invalid values, and NULL).

2

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.

3

An “available device extension” is a device extension supported by any physical device enumerated by instance.

4

Starting with Vulkan 1.2, vkGetInstanceProcAddr can resolve itself with a NULL instance pointer.

Valid Usage (Implicit)

  • If instance is not NULL, instance must be a valid VkInstance handle

  • 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 for each case.

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

core device-level Vulkan command

fp2

device

enabled extension device-level commands

fp2

any other case, not covered above

NULL
1

"*" means any representable value for the parameter (including valid values, invalid values, and NULL).

2

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)

  • device must be a valid VkDevice handle

  • 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);

3.1.1. 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.

3.1.2. 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.

3.2. 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)

  • 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
Valid Usage (Implicit)
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 reserved for future use.

  • 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)

  • sType must be VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO

  • Each pNext member of any structure (including this one) in the pNext chain must be either NULL or a pointer to a valid instance of VkDebugReportCallbackCreateInfoEXT, VkDebugUtilsMessengerCreateInfoEXT, VkValidationFeaturesEXT, or VkValidationFlagsEXT

  • The sType value of each struct in the pNext chain must be unique

  • flags must be 0

  • If pApplicationInfo is not NULL, pApplicationInfo must be a valid pointer to a valid VkApplicationInfo structure

  • If enabledLayerCount is not 0, ppEnabledLayerNames must be a valid pointer to an array of enabledLayerCount null-terminated UTF-8 strings

  • 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 VkFlags VkInstanceCreateFlags;

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

When creating a Vulkan instance for which you wish to disable validation checks, add a VkValidationFlagsEXT structure to the pNext chain of the VkInstanceCreateInfo structure, specifying the checks to be disabled.

// Provided by VK_EXT_validation_flags
typedef struct VkValidationFlagsEXT {
    VkStructureType                sType;
    const void*                    pNext;
    uint32_t                       disabledValidationCheckCount;
    const VkValidationCheckEXT*    pDisabledValidationChecks;
} VkValidationFlagsEXT;

  • sType is the type of this structure.

  • pNext is NULL or a pointer to a structure extending this structure.

  • disabledValidationCheckCount is the number of checks to disable.

  • pDisabledValidationChecks is a pointer to an array of VkValidationCheckEXT values specifying the validation checks to be disabled.

Valid Usage (Implicit)

  • sType must be VK_STRUCTURE_TYPE_VALIDATION_FLAGS_EXT

  • pDisabledValidationChecks must be a valid pointer to an array of disabledValidationCheckCount valid VkValidationCheckEXT values

  • disabledValidationCheckCount must be greater than 0

Possible values of elements of the VkValidationFlagsEXT::pDisabledValidationChecks array, specifying validation checks to be disabled, are:

// Provided by VK_EXT_validation_flags
typedef enum VkValidationCheckEXT {
    VK_VALIDATION_CHECK_ALL_EXT = 0,
    VK_VALIDATION_CHECK_SHADERS_EXT = 1,
} VkValidationCheckEXT;

  • VK_VALIDATION_CHECK_ALL_EXT specifies that all validation checks are disabled.

  • VK_VALIDATION_CHECK_SHADERS_EXT specifies that shader validation is disabled.

When creating a Vulkan instance for which you wish to enable or disable specific validation features, add a VkValidationFeaturesEXT structure to the pNext chain of the VkInstanceCreateInfo structure, specifying the features to be enabled or disabled.

// Provided by VK_EXT_validation_features
typedef struct VkValidationFeaturesEXT {
    VkStructureType                         sType;
    const void*                             pNext;
    uint32_t                                enabledValidationFeatureCount;
    const VkValidationFeatureEnableEXT*     pEnabledValidationFeatures;
    uint32_t                                disabledValidationFeatureCount;
    const VkValidationFeatureDisableEXT*    pDisabledValidationFeatures;
} VkValidationFeaturesEXT;

  • sType is the type of this structure.

  • pNext is NULL or a pointer to a structure extending this structure.

  • enabledValidationFeatureCount is the number of features to enable.

  • pEnabledValidationFeatures is a pointer to an array of VkValidationFeatureEnableEXT values specifying the validation features to be enabled.

  • disabledValidationFeatureCount is the number of features to disable.

  • pDisabledValidationFeatures is a pointer to an array of VkValidationFeatureDisableEXT values specifying the validation features to be disabled.

Valid Usage

  • If the pEnabledValidationFeatures array contains VK_VALIDATION_FEATURE_ENABLE_GPU_ASSISTED_RESERVE_BINDING_SLOT_EXT, then it must also contain VK_VALIDATION_FEATURE_ENABLE_GPU_ASSISTED_EXT

  • If the pEnabledValidationFeatures array contains VK_VALIDATION_FEATURE_ENABLE_DEBUG_PRINTF_EXT, then it must not contain VK_VALIDATION_FEATURE_ENABLE_GPU_ASSISTED_EXT

Valid Usage (Implicit)

  • sType must be VK_STRUCTURE_TYPE_VALIDATION_FEATURES_EXT

  • If enabledValidationFeatureCount is not 0, pEnabledValidationFeatures must be a valid pointer to an array of enabledValidationFeatureCount valid VkValidationFeatureEnableEXT values

  • If disabledValidationFeatureCount is not 0, pDisabledValidationFeatures must be a valid pointer to an array of disabledValidationFeatureCount valid VkValidationFeatureDisableEXT values

Possible values of elements of the VkValidationFeaturesEXT::pEnabledValidationFeatures array, specifying validation features to be enabled, are:

// Provided by VK_EXT_validation_features
typedef enum VkValidationFeatureEnableEXT {
    VK_VALIDATION_FEATURE_ENABLE_GPU_ASSISTED_EXT = 0,
    VK_VALIDATION_FEATURE_ENABLE_GPU_ASSISTED_RESERVE_BINDING_SLOT_EXT = 1,
    VK_VALIDATION_FEATURE_ENABLE_BEST_PRACTICES_EXT = 2,
    VK_VALIDATION_FEATURE_ENABLE_DEBUG_PRINTF_EXT = 3,
} VkValidationFeatureEnableEXT;

  • VK_VALIDATION_FEATURE_ENABLE_GPU_ASSISTED_EXT specifies that GPU-assisted validation is enabled. Activating this feature instruments shader programs to generate additional diagnostic data. This feature is disabled by default.

  • VK_VALIDATION_FEATURE_ENABLE_GPU_ASSISTED_RESERVE_BINDING_SLOT_EXT specifies that the validation layers reserve a descriptor set binding slot for their own use. The layer reports a value for VkPhysicalDeviceLimits::maxBoundDescriptorSets that is one less than the value reported by the device. If the device supports the binding of only one descriptor set, the validation layer does not perform GPU-assisted validation. This feature is disabled by default.

  • VK_VALIDATION_FEATURE_ENABLE_BEST_PRACTICES_EXT specifies that Vulkan best-practices validation is enabled. Activating this feature enables the output of warnings related to common misuse of the API, but which are not explicitly prohibited by the specification. This feature is disabled by default.

  • VK_VALIDATION_FEATURE_ENABLE_DEBUG_PRINTF_EXT specifies that the layers will process debugPrintfEXT operations in shaders and send the resulting output to the debug callback. This feature is disabled by default.

Possible values of elements of the VkValidationFeaturesEXT::pDisabledValidationFeatures array, specifying validation features to be disabled, are:

// Provided by VK_EXT_validation_features
typedef enum VkValidationFeatureDisableEXT {
    VK_VALIDATION_FEATURE_DISABLE_ALL_EXT = 0,
    VK_VALIDATION_FEATURE_DISABLE_SHADERS_EXT = 1,
    VK_VALIDATION_FEATURE_DISABLE_THREAD_SAFETY_EXT = 2,
    VK_VALIDATION_FEATURE_DISABLE_API_PARAMETERS_EXT = 3,
    VK_VALIDATION_FEATURE_DISABLE_OBJECT_LIFETIMES_EXT = 4,
    VK_VALIDATION_FEATURE_DISABLE_CORE_CHECKS_EXT = 5,
    VK_VALIDATION_FEATURE_DISABLE_UNIQUE_HANDLES_EXT = 6,
} VkValidationFeatureDisableEXT;

  • VK_VALIDATION_FEATURE_DISABLE_ALL_EXT specifies that all validation checks are disabled.

  • VK_VALIDATION_FEATURE_DISABLE_SHADERS_EXT specifies that shader validation is disabled. This feature is enabled by default.

  • VK_VALIDATION_FEATURE_DISABLE_THREAD_SAFETY_EXT specifies that thread safety validation is disabled. This feature is enabled by default.

  • VK_VALIDATION_FEATURE_DISABLE_API_PARAMETERS_EXT specifies that stateless parameter validation is disabled. This feature is enabled by default.

  • VK_VALIDATION_FEATURE_DISABLE_OBJECT_LIFETIMES_EXT specifies that object lifetime validation is disabled. This feature is enabled by default.

  • VK_VALIDATION_FEATURE_DISABLE_CORE_CHECKS_EXT specifies that core validation checks are disabled. This feature is enabled by default. If this feature is disabled, the shader validation and GPU-assisted validation features are also disabled.

  • VK_VALIDATION_FEATURE_DISABLE_UNIQUE_HANDLES_EXT specifies that protection against duplicate non-dispatchable object handles is disabled. This feature is enabled by default.

Note

Disabling checks such as parameter validation and object lifetime validation prevents the reporting of error conditions that can cause other validation checks to behave incorrectly or crash. Some validation checks assume that their inputs are already valid and do not always revalidate them.
Note

The VK_EXT_validation_features extension subsumes all the functionality provided in the VK_EXT_validation_flags extension.

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. Only the major and minor versions of the instance must match those 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.

Implicit layers must be disabled if they do not support a version at least as high as apiVersion. See the Vulkan Loader Specification and Architecture Overview document for additional information.

Note

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

  • sType must be VK_STRUCTURE_TYPE_APPLICATION_INFO

  • pNext must be NULL

  • If pApplicationName is not NULL, pApplicationName must be a null-terminated UTF-8 string

  • 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

  • All child objects created using instance must have been destroyed prior to destroying instance

  • If VkAllocationCallbacks were provided when instance was created, a compatible set of callbacks must be provided here

  • If no VkAllocationCallbacks were provided when instance was created, pAllocator must be NULL

Valid Usage (Implicit)

  • If instance is not NULL, instance must be a valid VkInstance handle

  • 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