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Interop with other graphics APIs

VMA provides some features that help with interoperability with other graphics APIs, e.g. OpenGL.

# Exporting memory

If you want to attach VkExportMemoryAllocateInfoKHR or other structure to pNext chain of memory allocations made by the library:

You can create Custom memory pools for such allocations. Define and fill in your VkExportMemoryAllocateInfoKHR structure and attach it to VmaPoolCreateInfo::pMemoryAllocateNext while creating the custom pool. Please note that the structure must remain alive and unchanged for the whole lifetime of the VmaPool, not only while creating it, as no copy of the structure is made, but its original pointer is used for each allocation instead.

If you want to export all memory allocated by VMA from certain memory types, also dedicated allocations or other allocations made from default pools, an alternative solution is to fill in VmaAllocatorCreateInfo::pTypeExternalMemoryHandleTypes. It should point to an array with VkExternalMemoryHandleTypeFlagsKHR to be automatically passed by the library through VkExportMemoryAllocateInfoKHR on each allocation made from a specific memory type. Please note that new versions of the library also support dedicated allocations created in custom pools.

You should not mix these two methods in a way that allows to apply both to the same memory type. Otherwise, VkExportMemoryAllocateInfoKHR structure would be attached twice to the pNext chain of VkMemoryAllocateInfo.

# Custom alignment

Buffers or images exported to a different API like OpenGL may require a different alignment, higher than the one used by the library automatically, queried from functions like vkGetBufferMemoryRequirements. To impose such alignment:

You can create Custom memory pools for such allocations. Set VmaPoolCreateInfo::minAllocationAlignment member to the minimum alignment required for each allocation to be made out of this pool. The alignment actually used will be the maximum of this member and the alignment returned for the specific buffer or image from a function like vkGetBufferMemoryRequirements, which is called by VMA automatically.

If you want to create a buffer with a specific minimum alignment out of default pools, use special function vmaCreateBufferWithAlignment(), which takes additional parameter minAlignment.

Note the problem of alignment affects only resources placed inside bigger VkDeviceMemory blocks and not dedicated allocations, as these, by definition, always have alignment = 0 because the resource is bound to the beginning of its dedicated block. You can ensure that an allocation is created as dedicated by using VMA_ALLOCATION_CREATE_DEDICATED_MEMORY_BIT. Contrary to Direct3D 12, Vulkan doesn't have a concept of alignment of the entire memory block passed on its allocation.

# Extended allocation information

If you want to rely on VMA to allocate your buffers and images inside larger memory blocks, but you need to know the size of the entire block and whether the allocation was made with its own dedicated memory, use function vmaGetAllocationInfo2() to retrieve extended allocation information in structure VmaAllocationInfo2.