We have acquired a vkGetInstanceProcAddr() function, through which we can load all other Vulkan API entry points in an OS-independent way.

Vulkan functions can be divided into three levels, which are global, instance, and device. Device-level functions are used to perform typical operations such as drawing, shader-modules creation, image creation, or data copying. Instance-level functions allow us to create logical devices. To do all this, and to load device and instance-level functions, we need to create an Instance. This operation is performed with global-level functions, which we need to load first.

1. Create a variable of type PFN_vkEnumerateInstanceExtensionProperties named vkEnumerateInstanceExtensionProperties.
2. Create a variable of type PFN_vkEnumerateInstanceLayerProperties named vkEnumerateInstanceLayerProperties.
3. Create a variable of type PFN_vkCreateInstance named vkCreateInstance.
4. Call vkGetInstanceProcAddr( nullptr, "vkEnumerateInstanceExtensionProperties" ), cast the result of this operation onto the PFN_vkEnumerateInstanceExtensionProperties type, and store it in a vkEnumerateInstanceExtensionProperties variable.
5. Call vkGetInstanceProcAddr( nullptr, "vkEnumerateInstanceLayerProperties" ), cast the result of this operation onto the PFN_vkEnumerateInstanceLayerProperties type, and store it in a vkEnumerateInstanceLayerProperties variable.
6. Call vkGetInstanceProcAddr( nullptr, "vkCreateInstance" ), cast the result of this operation onto a PFN_vkCreateInstance type, and store it in the vkCreateInstance variable.
7. Confirm that the operation succeeded by checking whether, values of all the preceding variables are not equal to nullptr.

In Vulkan, there are only three global-level functions: vkEnumerateInstanceExtensionProperties(), vkEnumerateInstanceLayerProperties(), and vkCreateInstance(). They are used during Instance creation to check, what instance-level extensions and layers are available and to create the Instance itself.

The process of acquiring global-level functions is similar to the loading function exported from the Vulkan Loader. That's why the most convenient way is to add the names of global-level functions to the ListOfVulkanFunctions.inl file as follows:

#ifndef GLOBAL_LEVEL_VULKAN_FUNCTION 
#define GLOBAL_LEVEL_VULKAN_FUNCTION( function ) 
#endif 

GLOBAL_LEVEL_VULKAN_FUNCTION( vkEnumerateInstanceExtensionProperties ) 
GLOBAL_LEVEL_VULKAN_FUNCTION( vkEnumerateInstanceLayerProperties ) 
GLOBAL_LEVEL_VULKAN_FUNCTION( vkCreateInstance ) 

#undef GLOBAL_LEVEL_VULKAN_FUNCTION

We don't need to change the VulkanFunctions.h and VulkanFunctions.h files, but we still need to implement the preceding recipe and load global-level functions as follows:

#define GLOBAL_LEVEL_VULKAN_FUNCTION( name )                      \
name = (PFN_##name)vkGetInstanceProcAddr( nullptr, #name );       \
if( name == nullptr ) {                                           \
  std::cout << "Could not load global-level function named: "     \
    #name << std::endl;                                           \
  return false;                                                   \
} 

#include "ListOfVulkanFunctions.inl" 

return true;

A custom GLOBAL_LEVEL_VULKAN_FUNCTION macro takes the function name and provides it to a vkGetInstanceProcAddr() function. It tries to load the given function and, in the case of a failure, returns nullptr. Any result returned by the vkGetInstanceProcAddr() function is cast onto a PFN_<name> type and stored in a proper variable.

In the case of a failure, a message is displayed so the user knows which function couldn't be loaded.

The following recipes in this chapter:

• Preparing for loading Vulkan API functions
• Loading function exported from a Vulkan Loader library
• Loading instance-level functions
• Loading device-level functions