How to Pass Struct by Value?

[sundararajan.athijegannathan at oracle.com]

Just pass the MemorySegment of the struct and that should work

-Sundar

On 30/09/20 12:06 pm, Michael Ennen wrote:
> I am messing around with DirectX 12 more and I am getting stuck on how to
> call the "GetCPUDescriptorHandleForHeapStart " method. It must take a
> struct by-value and not as a pointer reference.
> https://docs.microsoft.com/en-us/windows/win32/api/d3d12/nf-d3d12-id3d12descriptorheap-getcpudescriptorhandleforheapstart
>
> There seems to be a bit of an issue with that method as I see some Github
> issues talking about it's weird ABI, but I don't think I am hitting that
> issue (see https://github.com/halide/Halide/issues/5156 for example).
>
> I have the following:
>
> MemorySegment heapDescriptorVtbl =
> asSegment(ID3D12DescriptorHeap.lpVtbl$get(pHeapDescriptor),
> ID3D12DescriptorHeapVtbl.$LAYOUT());
> MemoryAddress getCPUDescriptorHandleForHeapStartAddr =
> ID3D12DescriptorHeapVtbl.GetCPUDescriptorHandleForHeapStart$get(heapDescriptorVtbl);
> var pRtvHandle = D3D12_CPU_DESCRIPTOR_HANDLE.allocate(scope);
> MethodHandle ID3D12DescriptorHeap_GetCPUDescriptorHandleForHeapStart =
> getInstance().downcallHandle(getCPUDescriptorHandleForHeapStartAddr,
> MethodType.methodType(void.class, MemoryAddress.class, MemoryAddress.class),
> FunctionDescriptor.ofVoid(C_POINTER, C_POINTER));
> ID3D12DescriptorHeap_GetCPUDescriptorHandleForHeapStart.invokeExact(
> pHeapDescriptor.address(), pRtvHandle.address());
>
> But it is not right as I am passing in D3D12_CPU_DESCRIPTOR_HANDLE as a
> pointer.
>
> I tried exploring the Panama API and looking at tests but just didn't find
> what I was looking for (how to pass a struct by value, if that's possible
> with the ABI semantics).
>
> My current work is here:
>
> https://github.com/brcolow/java-dx12/
>
> Thanks very much.