C Specification

Function pointers for all OpenXR functions can be obtained with the function xrGetInstanceProcAddr.

XrResult xrGetInstanceProcAddr(
    XrInstance                                  instance,
    const char*                                 name,
    PFN_xrVoidFunction*                         function);

Parameters

Parameter Descriptions
  • instance is the instance that the function pointer will be compatible with, or NULL for functions not dependent on any instance.

  • name is the name of the function to obtain.

  • function is the address of the function pointer to get.

Description

xrGetInstanceProcAddr itself is obtained in a platform- and loader- specific manner. Typically, the loader library will export this function 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 must export function symbols for all core OpenXR functions. Because of this, applications that use only the core OpenXR functions have no need to use xrGetInstanceProcAddr.

Because an application can call xrGetInstanceProcAddr before creating an instance, xrGetInstanceProcAddr returns a valid function pointer when the instance parameter is XR_NULL_HANDLE and the name parameter is one of the following strings:

xrGetInstanceProcAddr must return XR_ERROR_HANDLE_INVALID if name is not one of the above strings and instance is XR_NULL_HANDLE. xrGetInstanceProcAddr may return XR_ERROR_HANDLE_INVALID if name is not one of the above strings and instance is invalid but not XR_NULL_HANDLE.

xrGetInstanceProcAddr must return XR_ERROR_FUNCTION_UNSUPPORTED if instance is a valid instance and the string specified in name is not the name of an OpenXR core or enabled extension function.

If name is the name of an extension function, then the result returned by xrGetInstanceProcAddr will depend upon how the instance was created. If instance was created with the related extension’s name appearing in the XrInstanceCreateInfo::enabledExtensionNames array, then xrGetInstanceProcAddr returns a valid function pointer. If the related extension’s name did not appear in the XrInstanceCreateInfo::enabledExtensionNames array during the creation of instance, then xrGetInstanceProcAddr returns XR_ERROR_FUNCTION_UNSUPPORTED. Because of this, function pointers returned by xrGetInstanceProcAddr using one XrInstance may not be valid when used with objects related to a different XrInstance.

The returned function pointer is of type PFN_xrVoidFunction, and must be cast to the type of the function being queried.

The table below defines the various use cases for xrGetInstanceProcAddr and return value (“fp” is “function pointer”) for each case.

Table 1. xrGetInstanceProcAddr behavior
instance parameter name parameter return value

*

NULL

undefined

invalid instance

*

undefined

NULL

xrEnumerateInstanceExtensionProperties

fp

NULL

xrEnumerateApiLayerProperties

fp

NULL

xrCreateInstance

fp

NULL

* (any name not covered above)

NULL

instance

core OpenXR function

fp1

instance

enabled extension function for instance

fp1

instance

* (any name not covered above)

NULL

1

The returned function pointer must only be called with a handle (the first parameter) that is instance or a child of instance.

Valid Usage (Implicit)
Return Codes
On success, this command returns
  • XR_SUCCESS

On failure, this command returns
  • XR_ERROR_FUNCTION_UNSUPPORTED

  • XR_ERROR_VALIDATION_FAILURE

  • XR_ERROR_RUNTIME_FAILURE

  • XR_ERROR_HANDLE_INVALID

  • XR_ERROR_INSTANCE_LOST

  • XR_ERROR_OUT_OF_MEMORY

See Also

Document Notes

For more information, see the OpenXR Specification

This page is extracted from the OpenXR Specification. Fixes and changes should be made to the Specification, not directly.

Copyright (c) 2014-2021, The Khronos Group Inc.