How to Pass Struct by Value?

[Michael Ennen]

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