Somehow none of this MoltenVK stuff makes any comparison to Metal proper. I wonder if that’s intentional.
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“I don’t understand why some PC games have added Vk backends” as opposed to D3D12 backends. Haven’t seen any reports saying Vk is faster than D3D12, and the number of machines with Vk but not D3D12 is nearly (exactly?) 0
Choosing Vk in that scenario makes sense if you don’t /want/ to be locked into PC/Xbox without writing another backend, esp. given that DX12 and Vk are roughly the same complexity.
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1/7 Vk supports any combination of https://www.khronos.org/registry/vulkan/specs/1.0/man/html/VkMemoryPropertyFlagBits.html …, while D3D just has https://msdn.microsoft.com/en-us/library/dn770374(v=vs.85).aspx …. Vk supports any combination of https://www.khronos.org/registry/vulkan/specs/1.0/man/html/VkQueueFlagBits.html …, while D3D has just https://msdn.microsoft.com/en-us/library/dn770348(v=vs.85).aspx … (no combinations)
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2/7 Vk formats & image formats each individually need to be queried about what tiling they support https://www.khronos.org/registry/vulkan/specs/1.0/man/html/vkGetPhysicalDeviceFormatProperties.html …, while D3D has the same rules for every device https://msdn.microsoft.com/en-us/library/dn770442(v=vs.85).aspx …
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3/7 Each Vk resource may only be able to be placed in certain heaps https://www.khronos.org/registry/vulkan/specs/1.0/man/html/vkGetBufferMemoryRequirements.html …, while D3D doesn't seem to have this requirement. Vk has semaphores, fences, events, pipeline barriers, while D3D just has fences and resource barriers.
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4/7 Vk barriers have https://www.khronos.org/registry/vulkan/specs/1.0/man/html/vkCmdPipelineBarrier.html … and https://www.khronos.org/registry/vulkan/specs/1.0/man/html/VkBufferMemoryBarrier.html …, while D3D barriers have https://msdn.microsoft.com/en-us/library/dn986740(v=vs.85).aspx … and https://msdn.microsoft.com/en-us/library/dn986745(v=vs.85).aspx ….
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5/7 Creating Vk pipeline state requires knowing each render subpass & its dependencies https://www.khronos.org/registry/vulkan/specs/1.0/man/html/VkRenderPassCreateInfo.html … but D3D lets you swap render targets at any point https://msdn.microsoft.com/en-us/library/dn986884(v=vs.85).aspx …
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6/7 Vk's hello world has 3369 lines of code https://github.com/KhronosGroup/Vulkan-LoaderAndValidationLayers/blob/master/demos/cube.c … and D3D's hello world has 478 lines of code https://github.com/Microsoft/DirectX-Graphics-Samples/blob/22718ba0ea7be235fd00fd38b28b06cf30adf8e7/Samples/UWP/D3D12HelloWorld/src/HelloTexture/D3D12HelloTexture.cpp …
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7/7 So, no, Vk is not write-once-run-anywhere. It’s more like write-three-times-run-some-places. And if you’re going to write three times, you might as well do it using good APIs that each target platform natively supports.
End of conversation
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