We currently create statically sized descriptor pools, shared among
different descriptor types. Once we're unable to allocate a descriptor
set from a pool, we create a new pool. The unfortunate but predictable
consequence is that when we run out of descriptors of one type, we waste
any unallocated descriptors of the other types.
Dynamically adjusting the pool sizes could mitigate the issue, but it
seems non-trivial to handle all the edge cases, particularly in
situations where the descriptor count ratios change significantly
between frames. Instead, by storing only a single vkd3d descriptor type
in each Vulkan descriptor set we're able to create separate descriptor
pools for each vkd3d descriptor type, which also avoids the issue.
The main drawback of using separate descriptor sets for each descriptor
type is that we can no longer pack all bounded descriptor ranges into a
single descriptor set, potentially leaving fewer descriptor sets
available for unbounded ranges. That seems worth it, but we may end up
having to switch to a more complicated strategy if this ends up being a
problem on Vulkan implementations with a very limited number of
available descriptor sets.
ERR is used to indicate internal inconsistencies in vkd3d. Here that's
not the case, we simply have to forward the error condition to the
caller.
This fixes failures on the CI with llvmpipe, because the build we use is
compiled without support for VK_KHR_surface and related extensions.
Without LTO, gcc doesn't know that hresult_from_vk_result() will always return a
failure HRESULT for a failure VkResult, and so thinks that we might exit from
vkd3d_check_device_extensions() with a success HRESULT but without initializing
vk_extensions.
Currently the mutable descriptor set is repeated many times in the
pipeline layout in order to cover the indices for all the
descriptor types that would be present if mutable descriptors were
not used. This is useless and wasteful, but was necessary before
the descriptor sets backing the SRV-UAV-CBV heap were moved at the
end of the allocation table because descriptor set indices are
currently a compile-time constant in many places.
Now this is not needed any more and we can just avoid putting
many copies of the mutable descriptor set in the pipeline layout,
making it easier to meet Vulkan implementation limits.
So that when mutable descriptors are in use we can avoid putting
the other descriptor sets backing the SRV-UAV-CBV descriptor heap
in the pipeline layout altogether.
So we avoid hardcoding that it is number zero. There are two
goals here: first making the code easier to understand and
second allow reshuffling the descriptor set allocation in a
later commit.
The descriptor heap implementation is a rather central behavior element
in vkd3d, so it's useful to have all the relevant information logged
in a single place.
Slightly simplifies descriptor write addressing, and makes layouts
essentially the same as array layouts, differing only in the binding
details, and therefore easier to understand. This also simplifies the
addition of storage buffer bindings, which can all be added onto the end.
Allows descriptor set layouts to be created after all bindings are
mapped. This is less complex and fragile than the current scheme, and in
a future patch it will support separating descriptor types into different
sets. Descriptors on virtual heaps are currently allocated from pools
which contain an equal number of each descriptor type used by vkd3d, and
this can waste a significant amount of device memory.
