Vulkan-Docs/doc/specs/vulkan/chapters/initialization.txt

// Copyright (c) 2015-2017 Khronos Group. This work is licensed under a
// Creative Commons Attribution 4.0 International License; see
// http://creativecommons.org/licenses/by/4.0/

[[initialization]]
= Initialization

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

[[initialization-functionpointers]]
== Command Function Pointers

[open,refpage='vkGetInstanceProcAddr',desc='Return a function pointer for a command',type='protos',xrefs='PFN_vkVoidFunction']
--

Vulkan commands are not necessarily exposed statically on a platform.
Function pointers for all Vulkan commands can: be obtained with the command:

include::../api/protos/vkGetInstanceProcAddr.txt[]

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

fname: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.
Loaders are encouraged to export function symbols for all other core Vulkan
commands as well; if this is done, then applications that use only the core
Vulkan commands have no need to use fname:vkGetInstanceProcAddr.

The table below defines the various use cases for
fname:vkGetInstanceProcAddr and expected return value ("`fp`" is "`function
pointer`") for each case.

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

.vkGetInstanceProcAddr behavior
[width="80%",options="header"]
|====
| pname:instance   | pname:pName                                  | return value
| *                | `NULL`                                       | undefined
| invalid instance | *                                            | undefined
| `NULL`           | flink:vkEnumerateInstanceExtensionProperties | fp
| `NULL`           | flink:vkEnumerateInstanceLayerProperties     | fp
| `NULL`           | flink:vkCreateInstance                       | fp
| `NULL`           | * (any pname:pName not covered above)        | `NULL`
| instance         | core Vulkan command                          | fp^1^
| instance         | enabled instance extension commands for pname:instance    | fp^1^
| instance         | available device extension^2^ commands for pname:instance | fp^1^
| instance         | * (any pname:pName not covered above)        | `NULL`
|====

1::
    The returned function pointer must: only be called with a dispatchable
    object (the first parameter) that is pname:instance or a child of
    pname:instance.
    e.g. sname:VkInstance, sname:VkPhysicalDevice, sname:VkDevice,
    sname:VkQueue, or sname:VkCommandBuffer.

2::
    An "`available extension`" is an extension function supported by any of
    the loader, driver or layer.

include::../validity/protos/vkGetInstanceProcAddr.txt[]
--

[open,refpage='vkGetDeviceProcAddr',desc='Return a function pointer for a command',type='protos',xrefs='PFN_vkVoidFunction']
--

In order to support systems with multiple Vulkan implementations comprising
heterogeneous collections of hardware and software, the function pointers
returned by fname:vkGetInstanceProcAddr may: point to dispatch code, which
calls a different real implementation for different sname:VkDevice objects
(and objects created from them).
The overhead of this internal dispatch 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:

include::../api/protos/vkGetDeviceProcAddr.txt[]

The table below defines the various use cases for fname:vkGetDeviceProcAddr
and expected return value for each case.

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

.vkGetDeviceProcAddr behavior
[width="80%",options="header"]
|====
| pname:device   | pname:pName                           | return value
| `NULL`         | *                                     | undefined
| invalid device | *                                     | undefined
| device         | `NULL`                                | undefined
| device         | core Vulkan command                   | fp^1^
| device         | enabled extension commands            | fp^1^
| device         | * (any pname:pName not covered above) | `NULL`
|====

1::
    The returned function pointer must: only be called with a dispatchable
    object (the first parameter) that is pname:device or a child of
    pname:device.
    e.g. sname:VkDevice, sname:VkQueue, or sname:VkCommandBuffer.

include::../validity/protos/vkGetDeviceProcAddr.txt[]

--

[open,refpage='PFN_vkVoidFunction',desc='Dummy function pointer type returned by queries',type='funcpointers',xrefs='vkGetDeviceProcAddr vkGetInstanceProcAddr']
--

The definition of tlink:PFN_vkVoidFunction is:

include::../api/funcpointers/PFN_vkVoidFunction.txt[]

--

ifdef::VK_KHR_get_physical_device_properties2[]

=== Extending Physical Device From Device Extensions

When the <<VK_KHR_get_physical_device_properties2>> extension is enabled,
physical device extension commands and structures can: be used with a
physical device if the corresponding extension is enumerated by
flink:vkEnumerateDeviceExtensionProperties for that physical device, even
before a logical device has been created.

To obtain a function pointer for a physical-device command from a device
extension, an application can: use fname:vkGetInstanceProcAddr.
This function pointer may: point to dispatch code, which calls a different
real implementation for different sname:VkPhysicalDevice objects.
Behavior is undefined if an extension physical-device command is called on a
physical device that does not support the extension.

Device extensions may: define structures that can: be added to the
ptext:pNext chain of physical-device commands.
Behavior is undefined if such an extension structure is passed to a physical
device command for a physical device that does not support the extension.

endif::VK_KHR_get_physical_device_properties2[]


[[initialization-instances]]
== Instances

[open,refpage='VkInstance',desc='Opaque handle to a instance object',type='handles']
--

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

Instances are represented by sname:VkInstance handles:

include::../api/handles/VkInstance.txt[]

--

[open,refpage='vkCreateInstance',desc='Create a new Vulkan instance',type='protos']
--

To create an instance object, call:

include::../api/protos/vkCreateInstance.txt[]

  * pname:pCreateInfo points to an instance of slink:VkInstanceCreateInfo
    controlling creation of the instance.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pInstance points a sname:VkInstance handle in which the resulting
    instance is returned.

fname:vkCreateInstance verifies that the requested layers exist.
If not, fname:vkCreateInstance will return ename:VK_ERROR_LAYER_NOT_PRESENT.
Next fname: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, fname:vkCreateInstance must:
return ename:VK_ERROR_EXTENSION_NOT_PRESENT.
After verifying and enabling the instance layers and extensions the
sname: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 fname:vkCreateInstance time for the
creation to succeed.

.Valid Usage
****
  * [[VUID-vkCreateInstance-ppEnabledExtensionNames-01388]]
    All <<extended-functionality-extensions-dependencies, required
    extensions>> for each extension in the
    slink:VkInstanceCreateInfo::pname:ppEnabledExtensionNames list must:
    also be present in that list.
****

include::../validity/protos/vkCreateInstance.txt[]
--

[open,refpage='VkInstanceCreateInfo',desc='Structure specifying parameters of a newly created instance',type='structs']
--

The sname:VkInstanceCreateInfo structure is defined as:

include::../api/structs/VkInstanceCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:flags is reserved for future use.
  * pname:pApplicationInfo is `NULL` or a pointer to an instance of
    sname:VkApplicationInfo.
    If not `NULL`, this information helps implementations recognize behavior
    inherent to classes of applications.
    slink:VkApplicationInfo is defined in detail below.
  * pname:enabledLayerCount is the number of global layers to enable.
  * pname:ppEnabledLayerNames is a pointer to an array of
    pname:enabledLayerCount null-terminated UTF-8 strings containing the
    names of layers to enable for the created instance.
    See the <<extended-functionality-layers,Layers>> section for further
    details.
  * pname:enabledExtensionCount is the number of global extensions to
    enable.
  * pname:ppEnabledExtensionNames is a pointer to an array of
    pname:enabledExtensionCount null-terminated UTF-8 strings containing the
    names of extensions to enable.

include::../validity/structs/VkInstanceCreateInfo.txt[]
--

ifdef::VK_EXT_validation_flags[]
include::VK_EXT_validation_flags.txt[]
endif::VK_EXT_validation_flags[]


[open,refpage='VkApplicationInfo',desc='Structure specifying application info',type='structs']
--

The sname:VkApplicationInfo structure is defined as:

include::../api/structs/VkApplicationInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:pApplicationName is `NULL` or is a pointer to a null-terminated
    UTF-8 string containing the name of the application.
  * pname:applicationVersion is an unsigned integer variable containing the
    developer-supplied version number of the application.
  * pname: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.
  * pname:engineVersion is an unsigned integer variable containing the
    developer-supplied version number of the engine used to create the
    application.
  * pname:apiVersion is the version of the Vulkan API against which the
    application expects to run, encoded as described in the
    <<fundamentals-versionnum,API Version Numbers and Semantics>> section.
    If pname:apiVersion is 0 the implementation must: ignore it, otherwise
    if the implementation does not support the requested pname:apiVersion,
    or an effective substitute for pname:apiVersion, it must: return
    ename:VK_ERROR_INCOMPATIBLE_DRIVER.
    The patch version number specified in pname:apiVersion is ignored when
    creating an instance object.
    Only the major and minor versions of the instance must: match those
    requested in pname:apiVersion.

include::../validity/structs/VkApplicationInfo.txt[]
--

[open,refpage='vkDestroyInstance',desc='Destroy an instance of Vulkan',type='protos']
--

To destroy an instance, call:

include::../api/protos/vkDestroyInstance.txt[]

  * pname:instance is the handle of the instance to destroy.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.

.Valid Usage
****
  * [[VUID-vkDestroyInstance-instance-00629]]
    All child objects created using pname:instance must: have been destroyed
    prior to destroying pname:instance
  * [[VUID-vkDestroyInstance-instance-00630]]
    If sname:VkAllocationCallbacks were provided when pname:instance was
    created, a compatible set of callbacks must: be provided here
  * [[VUID-vkDestroyInstance-instance-00631]]
    If no sname:VkAllocationCallbacks were provided when pname:instance was
    created, pname:pAllocator must: be `NULL`
****

include::../validity/protos/vkDestroyInstance.txt[]
--