Backends: Vulkan: Add VK_EXT_descriptor_heap support (#9374)

[achaulk]

No description provided.

[ocornut]

I don’t know what this feature is.
Can you describe why it is needed?

[achaulk]

This extension brings DX12-style descriptor management to vulkan and is a hard break in how descriptors are managed. It eliminates descriptor pools and sets as well as a lot of other object management; the client app will write descriptors directly into it's own buffers instead

However, it is expected that any switching between descriptor heap and descriptor set commands will be quite slow and each invalidates all of the other's state so the only way to avoid that currently is a custom backend

[ocornut]

But it is required? aka is an app using descriptor management required to use it everywhere and can't let the Vulkan backend do it things the current way?

• Can you make sure that code follows coding style? space are if, no braces for single line block etc. The freelist may be modeled over the one used in your DX12 example.
• Why does the main.cpp changes requests so many new extensions? e.g. VK_KHR_BUFFER_DEVICE_ADDRESS_EXTENSION_NAME VK_KHR_MULTIVIEW_EXTENSION_NAME and many others?

Thank you.

[achaulk]

It's not strictly required but without there will likely be stalls before & after doing the backend draw due to having to switch modes. The expected usage is there is one heap of each type per app and you use it for everything - see the note https://docs.vulkan.org/features/latest/features/proposals/VK_EXT_descriptor_heap.html#_descriptor_heaps

That is the minimum set of extensions to get the validation layer to not complain about missing extensions