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= Vulkan Portability Extension
ifdef::site-gen-antora[]
TIP: The source for this sample can be found in the https://github.com/KhronosGroup/Vulkan-Samples/tree/main/samples/extensions/portability[Khronos Vulkan samples github repository].
endif::[]
== Overview
This tutorial, along with the accompanying example code, demonstrates the use of the https://www.khronos.org/registry/vulkan/specs/1.3-extensions/html/vkspec.html#VK_KHR_portability_subset[VK_KHR_portability_subset] extension.
When the VK_INSTANCE_CREATE_ENUMERATE_PORTABILITY_BIT_KHR is set in the `Instance` class, Vulkan will consider devices that aren't fully conformant such as https://github.com/KhronosGroup/MoltenVK[MoltenVk] to be identified as a conformant implementation.
When this happens, use the VkPhysicalDevicePortabilitySubsetPropertiesKHR extension with the https://www.khronos.org/registry/vulkan/specs/1.3-extensions/html/vkspec.html#vkGetPhysicalDeviceFeatures2[vkGetPhysicalDeviceFeatures2] as detailed below to get the list of supported/unsupported features.
This tutorial along with the accompanying code also demonstrates the use of the https://www.khronos.org/registry/vulkan/specs/1.3-extensions/html/vkspec.html#VkPhysicalDevicePortabilitySubsetPropertiesKHR[VkPhysicalDevicePortabilitySubsetPropertiesKHR] which is currently a beta khronos extension.
This extension provides a list of supported and unsupported parts of Vulkan on a non-conformant Vulkan instance.
Build with VK_ENABLE_BETA_EXTENSIONS set to enable this.
== Setup
NOTE: Enabling the extension globally is done inside the framework, see the `Instance` class in link:../../../framework/core/instance.cpp[instance.
cpp] for details.
To enable the extension for all samples, build with VKB_ENABLE_PORTABILITY defined.
Enabling the functionality for the portability subset is done by adding the extension to the list of extensions to enable at instance level.
The device instance can also be used to generate the subset of portability enabled device items.
As with all extensions, this is optional, and you should check if the extension is present before enabling it.
[,cpp]
----
uint32_t instance_extension_count;
VK_CHECK(vkEnumerateInstanceExtensionProperties(nullptr, &instance_extension_count, nullptr));
std::vector<VkExtensionProperties> available_instance_extensions(instance_extension_count);
VK_CHECK(vkEnumerateInstanceExtensionProperties(nullptr, &instance_extension_count, available_instance_extensions.data()));
bool debug_utils = false;
for (auto &available_extension : available_instance_extensions)
{
if (strcmp(available_extension.extensionName, VK_KHR_PORTABILITY_SUBSET_EXTENSION_NAME) == 0)
{
debug_utils = true;
extensions.push_back(VK_KHR_PORTABILITY_SUBSET_EXTENSION_NAME);
}
}
----
=== Asking the device for the list of supported features
NB: VkPhysicalDevicePortabilitySubsetFeaturesKHR is currently a beta extension and will only compile with the VK_ENABLE_BETA_EXTENSIONS definition set.
[,cpp]
----
VkPhysicalDevicePortabilitySubsetFeaturesKHR portability_features{};
portability_features.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_PORTABILITY_SUBSET_FEATURES_KHR;
----
We then pass this to the `pNext` member of our Physical Device Features creation structure, then call the vkGetPhysicalDeviceFeatures2 function, the structure will populate and can be queried:
[,cpp]
----
VkPhysicalDeviceFeatures2 device_features{};
device_features.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FEATURES_2;
device_features.pNext = &portability_features;
vkGetPhysicalDeviceFeatures2(get_device().get_gpu().get_handle(), &device_features);
----
