How to Pass Struct by Value?

[Jorn Vernee]

Once again formatting is getting messed up.

Uploaded a file here: http://cr.openjdk.java.net/~jvernee/ec.txt

Jorn

On 30/09/2020 11:47, Jorn Vernee wrote:
> Hi Micheal,
>
> When I look at the d3d12.h header, I only find this declaration of 
> GetCPUDescriptorHandleForHeapStart:
>
>         D3D12_CPU_DESCRIPTOR_HANDLE ( STDMETHODCALLTYPE 
> *GetCPUDescriptorHandleForHeapStart )(
>             ID3D12DescriptorHeap * This);
>
> Which is in ID3D12DescriptorHeapVtbl.
>
> The return type being defined as:
>
> typedef struct D3D12_CPU_DESCRIPTOR_HANDLE
>     {
>     SIZE_T ptr;
>     }     D3D12_CPU_DESCRIPTOR_HANDLE;
>
> I'd expect this to be linked and invoked as:
>
> MemorySegment heapDescriptorVtbl = 
> asSegment(ID3D12DescriptorHeap.lpVtbl$get(pHeapDescriptor), 
> ID3D12DescriptorHeapVtbl.$LAYOUT()); MemoryAddress 
> getCPUDescriptorHandleForHeapStartAddr = 
> ID3D12DescriptorHeapVtbl.GetCPUDescriptorHandleForHeapStart$get(heapDescriptorVtbl); 
> MethodHandle ID3D12DescriptorHeap_GetCPUDescriptorHandleForHeapStart = 
> getInstance().downcallHandle(getCPUDescriptorHandleForHeapStartAddr, 
> MethodType.methodType(MemorySegment.class, MemoryAddress.class), 
> FunctionDescriptor.of(D3D12_CPU_DESCRIPTOR_HANDLE.$LAYOUT(), 
> C_POINTER)); MemorySegment handle = (MemorySegment) 
> ID3D12DescriptorHeap_GetCPUDescriptorHandleForHeapStart.invokeExact(pHeapDescriptor.address()); 
> // ^^^ don't forget to close this after using
>
> The linker will take care of handling all the ABI details.
>
> HTH,
> Jorn
>
> On 30/09/2020 08:36, 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.