Fundamentals

This chapter introduces fundamental concepts including the Vulkan architecture and execution model, API syntax, queues, pipeline configurations, numeric representation, state and state queries, and the different types of objects and shaders. It provides a framework for interpreting more specific descriptions of commands and behavior in the remainder of the Specification.

Host and Device Environment

The Vulkan Specification assumes and requires: the following properties of the host environment with respect to Vulkan implementations:

• The host must have runtime support for 8, 16, 32 and 64-bit signed and unsigned twos-complement integers, all addressable at the granularity of their size in bytes.
• The host must have runtime support for 32- and 64-bit floating-point types satisfying the range and precision constraints in the Floating-Point Computation section.
• The representation and endianness of these types on the host must match the representation and endianness of the same types on every physical device supported.

Execution Model

This section outlines the execution model of a Vulkan system.

Vulkan exposes one or more devices, each of which exposes one or more queues which may process work asynchronously to one another. The set of queues supported by a device is partitioned into families. Each family supports one or more types of functionality and may contain multiple queues with similar characteristics. Queues within a single family are considered compatible with one another, and work produced for a family of queues can be executed on any queue within that family. This specification defines the following types of functionality that queues may support: graphics, compute, video decode, video encode, sparse memory management, and transfer.

Device memory is explicitly managed by the application. Each device may advertise one or more heaps, representing different areas of memory. Memory heaps are either device-local or host-local, but are always visible to the device. Further detail about memory heaps is exposed via memory types available on that heap. Examples of memory areas that may be available on an implementation include:

• device-local is memory that is physically connected to the device.
• device-local, host visible is device-local memory that is visible to the host.
• host-local, host visible is memory that is local to the host and visible to the device and host.

On other architectures, there may only be a single heap that can be used for any purpose.

Queue Operation

Vulkan queues provide an interface to the execution engines of a device. Commands for these execution engines are recorded into command buffers ahead of execution time, and then submitted to a queue for execution. Once submitted to a queue, command buffers will begin and complete execution without further application intervention, though the order of this execution is dependent on a number of implicit and explicit ordering constraints.

Work is submitted to queues using queue submission commands that typically take the form vkQueue* (e.g. vkQueueSubmit , vkQueueBindSparse ), and can take a list of semaphores upon which to wait before work begins and a list of semaphores to signal once work has completed. The work itself, as well as signaling and waiting on the semaphores are all queue operations. Queue submission commands return control to the application once queue operations have been submitted - they do not wait for completion.

There are no implicit ordering constraints between queue operations on different queues, or between queues and the host, so these may operate in any order with respect to each other. Explicit ordering constraints between different queues or with the host can be expressed with semaphores and fences.

Command buffer submissions to a single queue respect submission order and other implicit ordering guarantees, but otherwise may overlap or execute out of order. Other types of batches and queue submissions against a single queue (e.g. sparse memory binding) have no implicit ordering constraints with any other queue submission or batch. Additional explicit ordering constraints between queue submissions and individual batches can be expressed with semaphores and fences.

Before a fence or semaphore is signaled, it is guaranteed that any previously submitted queue operations have completed execution, and that memory writes from those queue operations are available to future queue operations. Waiting on a signaled semaphore or fence guarantees that previous writes that are available are also visible to subsequent commands.

Command buffer boundaries, both between primary command buffers of the same or different batches or submissions as well as between primary and secondary command buffers, do not introduce any additional ordering constraints. In other words, submitting the set of command buffers (which can include executing secondary command buffers) between any semaphore or fence operations execute the recorded commands as if they had all been recorded into a single primary command buffer, except that the current state is reset on each boundary. Explicit ordering constraints can be expressed with explicit synchronization primitives.

There are a few implicit ordering guarantees between commands within a command buffer, but only covering a subset of execution. Additional explicit ordering constraints can be expressed with the various explicit synchronization primitives.

Commands recorded in command buffers can perform actions, set state that persists across commands, synchronize other commands, or indirectly launch other commands, with some commands fulfilling several of these roles. The Command Properties section for each such command lists which of these roles the command takes:

Action

Action commands perform operations that can update values in memory. E.g. draw commands, dispatch commands.

State

State setting commands update the current state of a command buffer, affecting the operation of future action commands.

Synchronization

Synchronization commands impose ordering constraints on action commands, by introducing explicit execution and memory dependencies.

Indirection

Indirection commands execute other commands which were not directly recorded in the same command buffer.

Object Model

The devices, queues, and other entities in Vulkan are represented by Vulkan objects. At the API level, all objects are referred to by handles. There are two classes of handles, dispatchable and non-dispatchable. Dispatchable handle types are a pointer to an opaque type. This pointer may be used by layers as part of intercepting API commands, and thus each API command takes a dispatchable type as its first parameter. Each object of a dispatchable type must have a unique handle value during its lifetime.

Non-dispatchable handle types are a 64-bit integer type whose meaning is implementation-dependent. If the privateData feature is enabled for a VkDevice, each object of a non-dispatchable type created on that device must have a handle value that is unique among objects created on that device, for the duration of the object’s lifetime. Otherwise, non-dispatchable handles may encode object information directly in the handle rather than acting as a reference to an underlying object, and thus may not have unique handle values. If handle values are not unique, then destroying one such handle must not cause identical handles of other types to become invalid, and must not cause identical handles of the same type to become invalid if that handle value has been created more times than it has been destroyed.

All objects created or allocated from a VkDevice (i.e. with a VkDevice as the first parameter) are private to that device, and must not be used on other devices.

Object Lifetime

Objects are created or allocated by vkCreate* and vkAllocate* commands, respectively. Once an object is created or allocated, its structure is considered to be immutable, though the contents of certain object types is still free to change. Objects are destroyed or freed by vkDestroy* and vkFree* commands, respectively.

Objects that are allocated (rather than created) take resources from an existing pool object or memory heap, and when freed return resources to that pool or heap. While object creation and destruction are generally expected to be low-frequency occurrences during runtime, allocating and freeing objects can occur at high frequency. Pool objects help accommodate improved performance of the allocations and frees.

It is an application’s responsibility to track the lifetime of Vulkan objects, and not to destroy them while they are still in use.

The ownership of application-owned memory is immediately acquired by any Vulkan command it is passed into. Ownership of such memory must be released back to the application at the end of the duration of the command, unless that command was deferred, so that the application can alter or free this memory as soon as all the commands that acquired it have returned. If the command was deferred, ownership of such memory is released back to the application when the deferred operation is complete.

The following object types are consumed when they are passed into a Vulkan command and not further accessed by the objects they are used to create. They must not be destroyed in the duration of any API command they are passed into:

• VkShaderModule
• VkPipelineCache
• VkValidationCacheEXT

A VkRenderPass or VkPipelineLayout object passed as a parameter to create another object is not further accessed by that object after the duration of the command it is passed into. A VkRenderPass used in a command buffer follows the rules described below.

VkDescriptorSetLayout objects may be accessed by commands that operate on descriptor sets allocated using that layout, and those descriptor sets must not be updated with vkUpdateDescriptorSets after the descriptor set layout has been destroyed. Otherwise, a VkDescriptorSetLayout object is no longer referenced by an API command it is passed into once host execution of that command completes.

The application must not destroy any other type of Vulkan object until all uses of that object by the device (such as via command buffer execution) have completed.

The following Vulkan objects must not be destroyed while any command buffers using the object are in the pending state:

• VkEvent
• VkQueryPool
• VkBuffer
• VkBufferView
• VkImage
• VkImageView
• VkPipeline
• VkSampler
• VkSamplerYcbcrConversion
• VkDescriptorPool
• VkFramebuffer
• VkRenderPass
• VkCommandBuffer
• VkCommandPool
• VkDeviceMemory
• VkDescriptorSet
• VkIndirectCommandsLayoutNV
• VkIndirectCommandsLayoutEXT
• VkIndirectExecutionSetEXT
• VkAccelerationStructureNV
• VkAccelerationStructureKHR
• VkVideoSessionKHR
• VkVideoSessionParametersKHR

Destroying these objects will move any command buffers that are in the recording or executable state, and are using those objects, to the invalid state.

The following Vulkan objects must not be destroyed while any queue is executing commands that use the object:

• VkFence
• VkSemaphore
• VkCommandBuffer
• VkCommandPool

In general, objects can be destroyed or freed in any order, even if the object being freed is involved in the use of another object (e.g. use of a resource in a view, use of a view in a descriptor set, use of a pipeline library in another pipeline, use of a referenced pipeline for additional graphics shader groups in another pipeline, use of a referenced object for additional shader-related states in a set, use of a bottom level acceleration structure in an instance referenced by a top level acceleration structure, use of an object in a command buffer, binding of a memory allocation to a resource), as long as any object that uses the freed object is not further used in any way except to be destroyed or to be reset in such a way that it no longer uses the other object (such as resetting a command buffer). If the object has been reset, then it can be used as if it never used the freed object. An exception to this is when there is a parent/child relationship between objects. In this case, the application must not destroy a parent object before its children, except when the parent is explicitly defined to free its children when it is destroyed (e.g. for pool objects, as defined below).

VkCommandPool objects are parents of VkCommandBuffer objects. VkDescriptorPool objects are parents of VkDescriptorSet objects. VkDevice objects are parents of many object types (all that take a VkDevice as a parameter to their creation).

The following Vulkan objects have specific restrictions for when they can be destroyed:

• VkQueue objects cannot be explicitly destroyed. Instead, they are implicitly destroyed when the VkDevice object they are retrieved from is destroyed.
• Destroying a pool object implicitly frees all objects allocated from that pool. Specifically, destroying VkCommandPool frees all VkCommandBuffer objects that were allocated from it, and destroying VkDescriptorPool frees all VkDescriptorSet objects that were allocated from it.
• VkDevice objects can be destroyed when all VkQueue objects retrieved from them are idle, and all objects created from them have been destroyed.
  • This includes the following objects:
    • VkFence
    • VkSemaphore
    • VkEvent
    • VkQueryPool
    • VkBuffer
    • VkBufferView
    • VkImage
    • VkImageView
    • VkShaderModule
    • VkPipelineCache
    • VkPipeline
    • VkPipelineLayout
    • VkSampler
    • VkSamplerYcbcrConversion
    • VkDescriptorSetLayout
    • VkDescriptorPool
    • VkFramebuffer
    • VkRenderPass
    • VkCommandPool
    • VkCommandBuffer
    • VkDeviceMemory
    • VkValidationCacheEXT
    • VkAccelerationStructureNV
    • VkAccelerationStructureKHR
    • VkVideoSessionKHR
    • VkVideoSessionParametersKHR
• VkPhysicalDevice objects cannot be explicitly destroyed. Instead, they are implicitly destroyed when the VkInstance object they are retrieved from is destroyed.
• VkInstance objects can be destroyed once all VkDevice objects created from any of its VkPhysicalDevice objects have been destroyed.

External Object Handles

As defined above, the scope of object handles created or allocated from a VkDevice is limited to that logical device. Objects which are not in scope are said to be external. To bring an external object into scope, an external handle must be exported from the object in the source scope and imported into the destination scope.

Application Binary Interface

The mechanism by which Vulkan is made available to applications is platform- or implementation- defined. On many platforms the C interface described in this Specification is provided by a shared library. Since shared libraries can be changed independently of the applications that use them, they present particular compatibility challenges, and this Specification places some requirements on them.

Shared library implementations must use the default Application Binary Interface (ABI) of the standard C compiler for the platform, or provide customized API headers that cause application code to use the implementation’s non-default ABI. An ABI in this context means the size, alignment, and layout of C data types; the procedure calling convention; and the naming convention for shared library symbols corresponding to C functions. Customizing the calling convention for a platform is usually accomplished by defining calling convention macros appropriately in vk_platform.h.

On platforms where Vulkan is provided as a shared library, library symbols beginning with vk and followed by a digit or uppercase letter are reserved for use by the implementation. Applications which use Vulkan must not provide definitions of these symbols. This allows the Vulkan shared library to be updated with additional symbols for new API versions or extensions without causing symbol conflicts with existing applications.

Shared library implementations should provide library symbols for commands in the highest version of this Specification they support, and for Window System Integration extensions relevant to the platform. They may also provide library symbols for commands defined by additional extensions.

Command Syntax and Duration

The Specification describes Vulkan commands as functions or procedures using C99 syntax. Language bindings for other languages such as C++ and JavaScript may allow for stricter parameter passing, or object-oriented interfaces.

Vulkan uses the standard C types for the base type of scalar parameters (e.g. types from <stdint.h>), with exceptions described below, or elsewhere in the text when appropriate:

Commands that create Vulkan objects are of the form vkCreate* and take Vk*CreateInfo structures with the parameters needed to create the object. These Vulkan objects are destroyed with commands of the form vkDestroy*.

The last in-parameter to each command that creates or destroys a Vulkan object is pAllocator. The pAllocator parameter can be a non-NULL value, in which case allocations for the given object are delegated to an application provided callback. Refer to the Memory Allocation chapter for further details.

Commands that allocate Vulkan objects owned by pool objects are of the form vkAllocate*, and take Vk*AllocateInfo structures. These Vulkan objects are freed with commands of the form vkFree*. These objects do not take allocators; if host memory is needed, they will use the allocator that was specified when their parent pool was created.

Commands are recorded into a command buffer by calling API commands of the form vkCmd*. Each such command may have different restrictions on where it can be used: in a primary and/or secondary command buffer, inside and/or outside a render pass, and in one or more of the supported queue types. These restrictions are documented together with the definition of each such command.

The duration of a Vulkan command refers to the interval between calling the command and its return to the caller.

Lifetime of Retrieved Results

Information is retrieved from the implementation with commands of the form vkGet* and vkEnumerate*.

Unless otherwise specified for an individual command, the results are invariant; that is, they will remain unchanged when retrieved again by calling the same command with the same parameters, so long as those parameters themselves all remain valid.

Array Results

Some query commands of the form vkGet* and vkEnumerate* enable retrieving multiple results in the form of a return array. Such commands typically have two pointer arguments as follows:

• An element count pointer pointing to an integer variable, conventionally named as p*Count where * is the capitalized singular form of the name of the retrieved values.
• A pointer to an array where the result array is retrieved, conventionally named as p* where * is the capitalized plural form of the name of the retrieved values.

If such commands are called with the array pointer set to NULL, then the number of retrievable elements is returned in the variable pointed to by the element count pointer. Otherwise, the element count pointer must point to a variable set by the application to the number of elements in the return array, and on return the variable is overwritten with the number of elements actually written to the return array. If the input element count is less than the number of retrievable array elements, the query will write only as many elements to the return array as specified by the element count variable set by the application, and the command will return VK_INCOMPLETE instead of VK_SUCCESS, to indicate that not all retrievable array elements were returned.

Query commands that return one or more structures, regardless of whether they return a single or an array of structures with or without a pNext chain, may also contain arrays within those structures. Such return arrays are typically defined in the form of two members as follows:

• An integer value specifying the element count, conventionally named as *Count where * is the singular form of the name of the retrieved values.
• A pointer to an array where the result array is retrieved, conventionally named as p* where * is the capitalized plural form of the name of the retrieved values.

Analogously to query commands that return multiple results, if the command is called with the array pointer member of the output structure in question set to NULL, then the number of retrievable elements is returned in the element count member of that output structure. Otherwise, the element count must specify the number of elements in the return array, and on return the element count member is overwritten with the number of elements actually written to the return array. If the input element count is less than the number of retrievable array elements, the query will write only as many elements to the return array as specified by the input element count, and the command will return VK_INCOMPLETE instead of VK_SUCCESS, if the query command has a VkResult return type, to indicate that not all retrievable array elements were returned.

Regardless of the type of query command, any array pointer member of an output structure must either be NULL, or point to an application-allocated array. Query commands must not return a pointer to implementation allocated storage in any output structure.

Threading Behavior

Vulkan is intended to provide scalable performance when used on multiple host threads. All commands support being called concurrently from multiple threads, but certain parameters, or components of parameters are defined to be externally synchronized. This means that the caller must guarantee that no more than one thread is using such a parameter at a given time.

More precisely, Vulkan commands use simple stores to update the state of Vulkan objects. A parameter declared as externally synchronized may have its contents updated at any time during the host execution of the command. If two commands operate on the same object and at least one of the commands declares the object to be externally synchronized, then the caller must guarantee not only that the commands do not execute simultaneously, but also that the two commands are separated by an appropriate memory barrier (if needed).

Similarly the application must avoid any potential data hazard of application-owned memory that has its ownership temporarily acquired by a Vulkan command. While the ownership of application-owned memory remains acquired by a command the implementation may read the memory at any point, and it may write non-const qualified memory at any point. Parameters referring to non-const qualified application-owned memory are not marked explicitly as externally synchronized in the Specification.

If an application is using deferred host operations in a command, and that operation is successfully deferred, object parameters and application-owned memory passed to that command may be accessed at any time until the deferred operation is complete.

Many object types are immutable, meaning the objects cannot change once they have been created. These types of objects never need external synchronization, except that they must not be destroyed while they are in use on another thread. In certain special cases mutable object parameters are internally synchronized, making external synchronization unnecessary. Any command parameters that are not labeled as externally synchronized are either not mutated by the command or are internally synchronized. Additionally, certain objects related to a command’s parameters (e.g. command pools and descriptor pools) may be affected by a command, and must also be externally synchronized. These implicit parameters are documented as described below.

Parameters of commands that are externally synchronized are listed below.

For VkPipelineCache objects created with flags containing VK_PIPELINE_CACHE_CREATE_EXTERNALLY_SYNCHRONIZED_BIT, the above table is extended with the pipelineCache parameter to vkCreate*Pipelines being externally synchronized.

There are also a few instances where a command can take in an application-allocated list whose contents are externally synchronized parameters. In these cases, the caller must guarantee that at most one thread is using a given element within the list at a given time. These parameters are listed below.

In addition, there are some implicit parameters that need to be externally synchronized. For example, when a commandBuffer parameter needs to be externally synchronized, it implies that the commandPool from which that command buffer was allocated also needs to be externally synchronized. The implicit parameters and their associated object are listed below.

Valid Usage

Valid usage defines a set of conditions which must be met in order to achieve well-defined runtime behavior in an application. These conditions depend only on Vulkan state, and the parameters or objects whose usage is constrained by the condition.

The core layer assumes applications are using the API correctly. Except as documented elsewhere in the Specification, the behavior of the core layer to an application using the API incorrectly is undefined:, and may include program termination. However, implementations must ensure that incorrect usage by an application does not affect the integrity of the operating system, the Vulkan implementation, or other applications in the system using Vulkan. In particular, any guarantees made by an operating system about whether memory from one process can be visible to another process or not must not be violated by a Vulkan implementation for any memory allocation. Vulkan implementations are not required to make additional security or integrity guarantees beyond those provided by the OS unless explicitly directed by the application’s use of a particular feature or extension.

Some valid usage conditions have dependencies on runtime limits or feature availability. It is possible to validate these conditions against Vulkan’s minimum supported values for these limits and features, or some subset of other known values.

Valid usage conditions do not cover conditions where well-defined behavior (including returning an error code) exists.

Valid usage conditions should apply to the command or structure where complete information about the condition would be known during execution of an application. This is such that a validation layer or linter can be written directly against these statements at the point they are specified.

Valid usage conditions are described in a block labeled Valid Usage following each command or structure they apply to.

Usage Validation

Vulkan is a layered API. The lowest layer is the core Vulkan layer, as defined by this Specification. The application can use additional layers above the core for debugging, validation, and other purposes.

One of the core principles of Vulkan is that building and submitting command buffers should be highly efficient. Thus error checking and validation of state in the core layer is minimal, although more rigorous validation can be enabled through the use of layers.

Validation of correct API usage is left to validation layers. Applications should be developed with validation layers enabled, to help catch and eliminate errors. Once validated, released applications should not enable validation layers by default.

Implicit Valid Usage

Some valid usage conditions apply to all commands and structures in the API, unless explicitly denoted otherwise for a specific command or structure. These conditions are considered implicit, and are described in a block labeled Valid Usage (Implicit) following each command or structure they apply to. Implicit valid usage conditions are described in detail below.

Valid Usage for Object Handles

Any input parameter to a command that is an object handle must be a valid object handle, unless otherwise specified. An object handle is valid if:

• It has been created or allocated by a previous, successful call to the API. Such calls are noted in the Specification.
• It has not been deleted or freed by a previous call to the API. Such calls are noted in the Specification.
• Any objects used by that object, either as part of creation or execution, must also be valid.

The reserved values VK_NULL_HANDLE and NULL can be used in place of valid non-dispatchable handles and dispatchable handles, respectively, when explicitly called out in the Specification. Any command that creates an object successfully must not return these values. It is valid to pass these values to vkDestroy* or vkFree* commands, which will silently ignore these values.

Valid Usage for Pointers

Any parameter that is a pointer must be a valid pointer only if it is explicitly called out by a Valid Usage statement.

A pointer is valid if it points at memory containing values of the number and type(s) expected by the command, and all fundamental types accessed through the pointer (e.g. as elements of an array or as members of a structure) satisfy the alignment requirements of the host processor.

Valid Usage for Strings

Any parameter that is a pointer to char must be a finite sequence of values terminated by a null character, or if explicitly called out in the Specification, can be NULL.

Strings specified as UTF-8 encoded must not contain invalid UTF-8 sequences. See String Representation for additional information about strings.

Valid Usage for Enumerated Types

Any parameter of an enumerated type must be a valid enumerant for that type. Use of an enumerant is valid if the following conditions are true:

• The enumerant is defined as part of the enumerated type.
• The enumerant is not a value suffixed with _MAX_ENUM.
  • This value exists only to ensure that C enum types are 32 bits in size and must not be used by applications.
• If the enumerant is used in a function that has a VkInstance as its first parameter and either:
  • it was added by a core version that is supported and the value of VkApplicationInfo::apiVersion is greater than or equal to the version that added it; or
  • it was added by an instance extension that was enabled for the instance.
• If the enumerant is used in a function that has a VkPhysicalDevice object as its first parameter and either:
  • it was added by a core version that is supported by that device (as reported by VkPhysicalDeviceProperties::apiVersion);
  • it was added by an instance extension that was enabled for the instance; or
  • it was added by a device extension that is supported by that device.
• If the enumerant is used in a function that has any other dispatchable object as its first parameter and either:
  • it was added by a core version that is supported for the device (as reported by VkPhysicalDeviceProperties::apiVersion); or
  • it was added by a device extension that was enabled for the device.

Additionally, if maintenance5 is supported, any integer value representable in the range valid for the defined type is valid when used in a function that has a VkPhysicalDevice object as its first parameter. Physical device queries will either return results indicating lack of support, or ignore unsupported values when used as a bit flag in a Vk*Flags* parameter.

Any enumerated type returned from a query command or otherwise output from Vulkan to the application must not have a reserved value. Reserved values are values not defined by any extension for that enumerated type.

Valid Usage for Flags

Valid Usage for Structure Types

Any parameter that is a structure containing a sType member must have a value of sType which is a valid VkStructureType value matching the type of the structure.

Valid Usage for Structure Pointer Chains

Any parameter that is a structure containing a void* pNext member must have a value of pNext that is either NULL, or is a pointer to a valid extending structure, containing sType and pNext members as described in the Vulkan Documentation and Extensions document in the section Extending Structures. The set of structures connected by pNext pointers is referred to as a pNext chain.

Each structure included in the pNext chain must be defined at runtime by either:

• a core version which is supported
• an extension which is enabled
• a supported device extension in the case of physical-device-level functionality added by the device extension

Each type of extending structure must not appear more than once in a pNext chain, including any aliases. This general rule may be explicitly overridden for specific structures.

Any component of the implementation (the loader, any enabled layers, and drivers) must skip over, without processing (other than reading the sType and pNext members) any extending structures in the chain not defined by core versions or extensions supported by that component.

As a convenience to implementations and layers needing to iterate through a structure pointer chain, the Vulkan API provides two base structures. These structures allow for some type safety, and can be used by Vulkan API functions that operate on generic inputs and outputs.

Valid Usage for Nested Structures

The above conditions also apply recursively to members of structures provided as input to a command, either as a direct argument to the command, or themselves a member of another structure.

Specifics on valid usage of each command are covered in their individual sections.

Valid Usage for Extensions

Instance-level functionality or behavior added by an instance extension to the API must not be used unless that extension is supported by the instance as determined by vkEnumerateInstanceExtensionProperties, and that extension is enabled in VkInstanceCreateInfo.

Physical-device-level functionality or behavior added by an instance extension to the API must not be used unless that extension is supported by the instance as determined by vkEnumerateInstanceExtensionProperties, and that extension is enabled in VkInstanceCreateInfo.

Physical-device-level functionality or behavior added by a device extension to the API must not be used unless the conditions described in Extending Physical Device From Device Extensions are met.

Device-level functionality added by a device extension that is dispatched from a VkDevice, or from a child object of a VkDevice must not be used unless that extension is supported by the device as determined by vkEnumerateDeviceExtensionProperties, and that extension is enabled in VkDeviceCreateInfo.

Valid Usage for Newer Core Versions

Physical-device-level functionality or behavior added by a new core version of the API must not be used unless it is supported by the physical device as determined by VkPhysicalDeviceProperties::apiVersion and the specified version of VkApplicationInfo::apiVersion.

Device-level functionality or behavior added by a new core version of the API must not be used unless it is supported by the device as determined by VkPhysicalDeviceProperties::apiVersion and the specified version of VkApplicationInfo::apiVersion.

VkResult Return Codes

Numeric Representation and Computation

Implementations normally perform computations in floating-point, and must meet the range and precision requirements defined under Floating-Point Computation below.

These requirements only apply to computations performed in Vulkan operations outside of shader execution, such as texture image specification and sampling, and per-fragment operations. Range and precision requirements during shader execution differ and are specified by the Precision and Operation of SPIR-V Instructions section.

In some cases, the representation and/or precision of operations is implicitly limited by the specified format of vertex or texel data consumed by Vulkan. Specific floating-point formats are described later in this section.

Floating-Point Computation

Most floating-point computation is performed in SPIR-V shader modules. The properties of computation within shaders are constrained as defined by the Precision and Operation of SPIR-V Instructions section.

Some floating-point computation is performed outside of shaders, such as viewport and depth range calculations. For these computations, we do not specify how floating-point numbers are to be represented, or the details of how operations on them are performed, but only place minimal requirements on representation and precision as described in the remainder of this section.

We require simply that numbers’ floating-point parts contain enough bits and that their exponent fields are large enough so that individual results of floating-point operations are accurate to about 1 part in 10⁵. The maximum representable magnitude for all floating-point values must be at least 2³².

• x × 0 = 0 × x = 0 for any non-infinite and non-NaN x.
• 1 × x = x × 1 = x.
• x + 0 = 0 + x = x.
• 0⁰ = 1.

Occasionally, further requirements will be specified. Most single-precision floating-point formats meet these requirements.

The special values Inf and -Inf encode values with magnitudes too large to be represented; the special value NaN encodes Not A Number values resulting from undefined: arithmetic operations such as 0 / 0. Implementations may support Inf and NaN in their floating-point computations. Any computation which does not support either Inf or NaN, for which that value is an input or output will yield an undefined: value.

Floating-Point Format Conversions

When a value is converted to a defined floating-point representation, finite values falling between two representable finite values are rounded to one or the other. The rounding mode is not defined. Finite values whose magnitude is larger than that of any representable finite value may be rounded either to the closest representable finite value or to the appropriately signed infinity. For unsigned destination formats any negative values are converted to zero. Positive infinity is converted to positive infinity; negative infinity is converted to negative infinity in signed formats and to zero in unsigned formats; and any NaN is converted to a NaN.

16-Bit Floating-Point Numbers

16-bit floating-point numbers are defined in the 16-bit floating-point numbers section of the Khronos Data Format Specification.

Unsigned 11-Bit Floating-Point Numbers

Unsigned 11-bit floating-point numbers are defined in the Unsigned 11-bit floating-point numbers section of the Khronos Data Format Specification.

Unsigned 10-Bit Floating-Point Numbers

Unsigned 10-bit floating-point numbers are defined in the Unsigned 10-bit floating-point numbers section of the Khronos Data Format Specification.

General Requirements

Any representable floating-point value in the appropriate format is legal as input to a Vulkan command that requires floating-point data. The result of providing a value that is not a floating-point number to such a command is unspecified, but must not lead to Vulkan interruption or termination. For example, providing a negative zero (where applicable) or a denormalized number to a Vulkan command must yield deterministic results, while providing a NaN or Inf yields unspecified results.

Some calculations require division. In such cases (including implied divisions performed by vector normalization), division by zero produces an unspecified result but must not lead to Vulkan interruption or termination.

Fixed-Point Data Conversions

When generic vertex attributes and pixel color or depth components are represented as integers, they are often (but not always) considered to be normalized. Normalized integer values are treated specially when being converted to and from floating-point values, and are usually referred to as normalized fixed-point.

In the remainder of this section, b denotes the bit width of the fixed-point integer representation. When the integer is one of the types defined by the API, b is the bit width of that type. When the integer comes from an image containing color or depth component texels, b is the number of bits allocated to that component in its specified image format.

The signed and unsigned fixed-point representations are assumed to be b-bit binary two’s-complement integers and binary unsigned integers, respectively.

Conversion From Normalized Fixed-Point to Floating-Point

Unsigned normalized fixed-point integers represent numbers in the range [0,1]. The conversion from an unsigned normalized fixed-point value c to the corresponding floating-point value f is defined as

Signed normalized fixed-point integers represent numbers in the range [-1,1]. The conversion from a signed normalized fixed-point value c to the corresponding floating-point value f is performed using

Only the range [-2^b-1 + 1, 2^b-1 - 1] is used to represent signed fixed-point values in the range [-1,1]. For example, if b = 8, then the integer value -127 corresponds to -1.0 and the value 127 corresponds to 1.0. This equation is used everywhere that signed normalized fixed-point values are converted to floating-point.

Note that while zero is exactly expressible in this representation, one value (-128 in the example) is outside the representable range, and implementations must clamp it to -1.0. Where the value is subject to further processing by the implementation, e.g. during texture filtering, values less than -1.0 may be used but the result must be clamped before the value is returned to shaders.

Conversion From Floating-Point to Normalized Fixed-Point

The conversion from a floating-point value f to the corresponding unsigned normalized fixed-point value c is defined by first clamping f to the range [0,1], then computing

• c = convertFloatToUint(f × (2^b - 1), b)

where convertFloatToUint(r,b) returns one of the two unsigned binary integer values with exactly b bits which are closest to the floating-point value r. Implementations should round to nearest. If r is equal to an integer, then that integer value must be returned. In particular, if f is equal to 0.0 or 1.0, then c must be assigned 0 or 2^b - 1, respectively.

The conversion from a floating-point value f to the corresponding signed normalized fixed-point value c is performed by clamping f to the range [-1,1], then computing

• c = convertFloatToInt(f × (2^b-1 - 1), b)

where convertFloatToInt(r,b) returns one of the two signed two’s-complement binary integer values with exactly b bits which are closest to the floating-point value r. Implementations should round to nearest. If r is equal to an integer, then that integer value must be returned. In particular, if f is equal to -1.0, 0.0, or 1.0, then c must be assigned -(2^b-1 - 1), 0, or 2^b-1 - 1, respectively.

This equation is used everywhere that floating-point values are converted to signed normalized fixed-point.

String Representation

Strings passed into and returned from Vulkan API commands are usually defined to be null-terminated and UTF-8 encoded.

When a UTF-8 string is returned from a Vulkan API query, it is returned in a fixed-length buffer of C char. For example, a string returned in VkPhysicalDeviceProperties::deviceName has maximum length VK_MAX_PHYSICAL_DEVICE_NAME_SIZE, and a string returned in VkExtensionProperties::extensionName has maximum length VK_MAX_EXTENSION_NAME_SIZE. The string, including its null terminator, will always fit completely within this buffer. If the string is shorter than the buffer size, the contents of char in the buffer following the null terminator are undefined:.

When a UTF-8 string is passed into a Vulkan API, such as VkDeviceCreateInfo::ppEnabledExtensionNames, there is no explicit limit on the length of that string. However, the string must contain a valid UTF-8 encoded string and must be null-terminated.

Common Object Types

Some types of Vulkan objects are used in many different structures and command parameters, and are described here. These types include offsets, extents, and rectangles.

Offsets

Offsets are used to describe a pixel location within an image or framebuffer, as an (x,y) location for two-dimensional images, or an (x,y,z) location for three-dimensional images.

Extents

Extents are used to describe the size of a rectangular region of pixels within an image or framebuffer, as (width,height) for two-dimensional images, or as (width,height,depth) for three-dimensional images.

Rectangles

Structure Types

API Name Aliases

A small number of APIs did not follow the naming conventions when initially defined. For consistency, when we discover an API name that violates the naming conventions, we rename it in the Specification, XML, and header files. For backwards compatibility, the original (incorrect) name is retained as a typo alias. The alias is deprecated and should not be used, but will be retained indefinitely.