Definition (or not) of IDXGIResource methods

[Ben "Root" Anderson]

I've been studying the DXGI code with an eye for implementing the
DirectX-side shared resource functionality so that an application
would hopefully be able to share Direct3D textures with a Vulkan
instance, and what I'm seeing has me rather confused.

IDXGIResource appears to be declared, with a number of methods, in
include/dxgi.idl. I'm not clear on what exactly an IDL file is, but my
impression is it's similar to a specfile, except for headers of C++
interfaces. In any case, none of the methods declared appear to have
any definition anywhere in Wine. The logical conclusion would be
they're automatically generated stubs.

But that doesn't make sense, because the DXGI test at
dlls/dxgi/tests/device.c calls IDXGIResource_GetUsage and appears to
expect it to succeed, implying that it's implemented *somewhere*. What
am I missing?