1 Known Issues

Alexandre Julliard edited this page 2024-09-02 18:17:49 +02:00

Vkd3d is considered as work-in-progress, there are known issues that have to be resolved. Moreover, there are some incompatibilities between Vulkan and Direct3D 12.

Issue	Description	Current implementation	Possible solutions
NULL descriptors	Vulkan doesn't support NULL descriptors.	NULL descriptors are currently emulated using dummy resources. Sparse resources are used when `residencyNonResidentStrict` is supported. The current solution doesn't handle `resinfo` and `bufinfo` instructions correctly.
Indirect draws	In Direct3D 12 indirect draws can update vertex buffer views, index buffer views, root constants and root descriptors.	Not supported in Vulkan.	A Vulkan extension. It could be emulated in an inefficient way.
Memory object residency	Memory object residency management doesn't exist in Vulkan. In Direct3D 12 resources and heaps can be evicted. Resource descriptors are still valid after a resource is made resident again.		We can try to evict memory manually (e.g. using sparse bindings).
Queries initial state	Queries are initially in the available state in Direct3D 12. Results are all equal to zero.	We track the query state, and fill buffer with zeroes when a query wasn't issued. The current implementation doesn't handle command lists executed out-of-order.
Texture array views	Texture array views and textures views are incompatible in Vulkan.
Descriptor heaps	Direct3D 12 and Vulkan binding models are largely different. It seems to be implied that Direct3D 12 CBV/SRV/UAV descriptor heaps exist in GPU memory, but there's no real equivalent for that in Vulkan. Vulkan descriptor sets are probably the closest match, but among others have the issue that the descriptor type (CBV, SRV or UAV) would need to be declared in advance, while in Direct3D 12 these can be mixed freely within the descriptor heap. Run-time translation from Direct3D 12 binding model to Vulkan binding model is expected to introduce a noticeable overhead.
CPU descriptor heaps	Direct3D 12 allows to create and prepare descriptors in CPU heaps. Descriptors from CPU descriptor heaps can be copied to shader-visible descriptor heaps. In Vulkan, there are only shared-visibile descriptor sets, and `VkCopyDescriptorSet` is implemented very inefficiently on some drivers.
Descriptor heaps concurrency	Some apps appear to concurrently overwrite descriptors in descriptor heaps. We need to confirm that this works reliably on Windows. It might not be a problem on Windows because implementations might simply write or copy descriptors data in memory. However, in our translation layer we have to manage VkImageView objects and potentially reference count them.
Descriptors for destroyed resources	Apps keep descriptors for destroyed resources in descriptor heaps. This is problematic and may lead to invalid usage in Vulkan.
ID3D12Fence	ID3D12Fence have an associated UINT64 value (see also timeline semaphores). In addition, ID3D12Fence can be signaled by GPU or CPU, and can also be waited for on CPU or ID3D12CommandQueue. Moreover, it's possible to signal native Win32 events when a fence reaches a certain value. In Vulkan, there is no way to signal native synchronization objects (e.g. HANDLEs to Win32 events or file descriptors) when, e.g. VkFence is signaled.		Timeline semaphores.
Sampler border color	In Direct3D 12 the sampler border color is defined as a float4 vector. In Vulkan the border color is constrained by the values of the VkBorderColor enum. (It might not be that important because we haven't encountered application which needs this yet).
Separate resource state for depth-stencil	In Direct3D, the depth aspect and the stencil aspect of an image can be in different image layouts.		Vulkan extension.
Out-of-bounds resource access	Vulkan doesn't give the same guarantees as Direct3D 12 when it comes to out-of-bounds resource access.
D3D12_DEFAULT_RESOURCE_PLACEMENT_ALIGNMENT	On radv with AMD Polaris GPUs, the required alignment for textures may be higher than 0x10000 (D3D12_DEFAULT_RESOURCE_PLACEMENT_ALIGNMENT), e.g. 0x20000 or 0x40000. World of Warcraft aligns only to D3D12_DEFAULT_RESOURCE_PLACEMENT_ALIGNMENT and ignores the alignment returned from `GetResourceAllocationInfo()`.	We currently allocate additional device memory when the heap offset is misaligned.
Swapchain	sRGB views. Scaling. Present mode without recreating.	We currently use additional set of images and blit from them to the real swapchain.
Conditional rendering	In D3D12, 64-bit values are used. `VK_EXT_conditional_rendering` uses 32-bit values. In D3D12, conditional rendering affects copy commands.	We do what the `VK_EXT_conditional_rendering` extension does.
Binary occlusion queries	D3D12 guarantees binary occlusion queries result in only 0 and 1.
Strip cut value	In Vulkan the strip cut value is derived from the index format. In Direct3D 12 0xffff or 0xffffffff can be used as the strip cut value with 16-bit and 32-bit index buffer formats.	Not supported in Vulkan.
GPU virtual addresses	In Direct3D 12, vertex buffers, index buffers, stream output buffers and root descriptors are bound using GPU virtual addresses. In Vulkan, VkBuffer objects with an offset are used instead.	Fake virtual addresses are allocated for buffers. Virtual addresses have to be resolved to VkBuffer and an offset. The resolving of GPU virtual address introduces unnecessary overhead.	`VK_EXT_device_buffer_address` can be used for root descriptors. Unfortunately, the extension doesn't help with vertex, index and stream output buffers. The extension also introduces some complications, e.g. multiple buffers can be bound to the same virtual memory address. Ideally, we could bind vertex, index and stream output buffers using `VkDeviceAddress` in Vulkan.
`GetResourceAllocationInfo()`	In Vulkan, a resource needs to be created to get allocation info.	We create temporary resources to get allocation info.
`SetEventOnCompletion()` / `SetEventOnMultipleFenceCompletion()`		We have a separate thread that signals Win32 events.	Timeline semaphores.
Copy between depth-stencil and color formats	In Direct3D 12 it is possible to copy data between compatible color and depth-stencil resources.	We currently use a temporary buffer to perform the copy operation.	We should implement the copy operation in shaders for graphics and compute queues.
Dynamic states	In Direct3D 12 the following states are dynamic: vertex buffer strides, the primitive topology and viewport/scissor counts. In Vulkan, those states require compiling a new pipeline. The primitive topology type is still specified when Direct3D 12 pipeline states are created (one of points, lines, triangles, or patches).	Vulkan pipelines are created on draw call time when we know all parameters to compile the pipeline.	Add pipeline cache. Compile pipelines speculatively.