CODEWITHSUNDEEP
vulkangpu
Krupip
Krupip

Reputation: 4892

Do enabled debug extensions and validation layers need to be added to the device when created if are already added to the instance?

After looking at the Vulkan Tutorial again recently, I noticed some of my projects deviate from it. One of the things the vulkan tutorial does is add debugextensions and validation layers at the instance level and then do the same thing at the device level. During the creation of a new project I realized that I had forgotten to set 

VkDeviceCreateInfo::enabledExtensionCount, 
VkDeviceCreateInfo::ppEnabledExtensionNames, 
VkDeviceCreateInfo::enabledLayerCount, and 
VkDeviceCreateInfo::ppEnabledLayerNames

to use debug extension and validation layers. Compilation not only worked fine with out them, but validation layers and debug extensions also appeared to not be impacted by this (and worked as well, I was able to set object names and see device errors). This made me wonder what the point was of including this information again for the device. I understand a device might have specific extensions, but do I really need set the exact same validation layer flags and extension names every time I create a new VkDevice?

Upvotes: 1

Views: 869

Answers (1)

krOoze
krOoze

Reputation: 13306

VK_EXT_debug_utils (and VK_EXT_debug_report too) is an instance extension. You should not be enable them for device too. If you try the driver should fail with VK_ERROR_EXTENSION_NOT_PRESENT.

As for layers, device layers were deprecated long time ago. Instance layers can now work at device level too. Make use of this compatibility note in the specification:

In order to maintain compatibility with implementations released prior to device-layer deprecation, applications should still enumerate and enable device layers. The behavior of vkEnumerateDeviceLayerProperties and valid usage of the ppEnabledLayerNames member of VkDeviceCreateInfo maximizes compatibility with applications written to work with the previous requirements.

The updated drivers that know about the change behave like this:

The list of layers enumerated by vkEnumerateDeviceLayerProperties must be exactly the sequence of layers enabled for the instance.

But if you are lazy (or check driver version) you can simply provide the list you get from vkEnumerateDeviceLayerProperties or nullptr. Either should work on updated drivers.

Upvotes: 3

Related Questions