Vulkan commands are not necessarily exposed statically on a platform. Function pointers for all Vulkan commands can be obtained with the command:
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.
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 vkGetInstanceProcAddr
.
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.
Table 3.1. vkGetInstanceProcAddr behavior
instance | pName | return value |
---|---|---|
* |
| undefined |
invalid instance | * | undefined |
| fp | |
| fp | |
| fp | |
| * (any |
|
instance | core Vulkan command | fp1 |
instance | enabled instance extension commands for | fp1 |
instance | available device extension2 commands for | fp1 |
instance | * (any |
|
instance
or a child of
instance
.
e.g. VkInstance
, VkPhysicalDevice
, VkDevice
,
VkQueue
, or VkCommandBuffer
.
In order to support systems with multiple Vulkan implementations comprising
heterogeneous collections of hardware and software, the function pointers
returned by vkGetInstanceProcAddr
may point to dispatch code, which
calls a different real implementation for different 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:
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.
Table 3.2. vkGetDeviceProcAddr behavior
device | pName | return value |
---|---|---|
| * | undefined |
invalid device | * | undefined |
device |
| undefined |
device | core Vulkan command | fp1 |
device | enabled extension commands | fp1 |
device | * (any |
|
device
or a child of
device
.
e.g. VkDevice
, VkQueue
, or VkCommandBuffer
.
The definition of PFN_vkVoidFunction
is:
typedef void (VKAPI_PTR *PFN_vkVoidFunction)(void);