How to Pass Struct by Value?

[Michael Ennen]

See also:

https://github.com/wolfgangfengel/graphicsdemoskeleton/blob/ba11402b6027ea14322bc430a23f2aadf3c0b11c/DirectX%2012/01_Skeleton/Window.c#L263

On Wed, Sep 30, 2020 at 11:45 AM Michael Ennen <mike.ennen at gmail.com> wrote:

> Ah yes I should have mentioned that this is actually an error with the
> unsupported DirectX 12 C API.
>
> See the following:
>
>             // Even though GetCPUDescriptorHandleForHeapStart is
> documented as taking no arguments (except for the
>             // this pointer), to use from C code it needs to take an
> additional rtvHandle argument, see, for example:
>             //
> https://joshstaiger.org/notes/C-Language-Problems-in-Direct3D-12-GetCPUDescriptorHandleForHeapStart.html
>             //
> https://github.com/curldivergence/dx12bindings/blob/841974943b7fbbd146d5372e9b496a9d72daf771/build.rs#L33
>
> On Wed, Sep 30, 2020 at 2:55 AM Jorn Vernee <jorn.vernee at oracle.com>
> wrote:
>
>> 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.
>>
>
>
> --
> Michael Ennen
>


-- 
Michael Ennen