[Jasper_]

D3D12 is very different from D3D11, but still has a lot in common. We started our port by reusing most of the same DXGI code and getting what we called our "sprites" rendering correctly (2D quads, used by the loading screen, and our debug UI). We were able to reuse a lot of code, including all of our existing HLSL shaders. None of that would work with Vulkan, at least without a lot more work (which we eventually did).

The parts that were D3D12-specific were definitely the parts that would overlap more with Vulkan: the work to switch to PSO (Pipeline State Objects), the addition of all the barriers all over the rendering code, the synchronization work, all of that work could be shared between D3D12 and Vulkan.