[PATCH 2/2] windowscodecs: Add support for IMILBitmapScaler interface.

[Vincent Povirk (they/them)]

The rule, as I understand it, is that all interfaces should return the
same pointer when queried for IUnknown. It doesn't have to be
discoverable by any other IID.

I'm not sure if that applies to interfaces generally or just IUnknown.
Mono's COM code (and probably .NET's as well) relies on it for
IUnknown.

On Tue, May 14, 2019 at 5:01 AM Dmitry Timoshkov <dmitry at baikal.ru> wrote:
>
> "Vincent Povirk (they/them)" <vincent at codeweavers.com> wrote:
>
> > +static HRESULT WINAPI
> > IMILBitmapScaler_QueryInterface(IMILBitmapScaler *iface, REFIID iid,
> > +    void **ppv)
> > +{
> > +    BitmapScaler *This = impl_from_IMILBitmapScaler(iface);
> > +
> > +    TRACE("(%p,%s,%p)\n", iface, debugstr_guid(iid), ppv);
> > +
> > +    if (!ppv) return E_INVALIDARG;
> > +
> > +    if (IsEqualIID(&IID_IUnknown, iid) ||
> > +        IsEqualIID(&IID_IMILBitmapScaler, iid) ||
> > +        IsEqualIID(&IID_IMILBitmapSource, iid))
> > +    {
> > +        IUnknown_AddRef(&This->IMILBitmapScaler_iface);
> >
> > This violates COM rules by returning a different IUnknown pointer
> > depending on the interface queried. Does native do that?
>
> I've added more tests for IMILBitmapScaler_QueryInterface() behaviour,
> and under Windows for IID_IUnknown it returns some strange interface
> pointer that doesn't match other public interfaces. Then I added the
> same test for IWICBitmap_QueryInterface() and it also returns some
> strange interface for IID_IUnknown. So both QI implementations in Wine
> have similar problems when queried for IID_IUnknown. Or do you mean
> some other COM rule violation in the comment above?
>
> --
> Dmitry.