Registering remote font file loader

[miquik]

Hi, Sorry I'm here again with another problem. I follow this tutorial creating-a-custom-font-set-using-known-remote-fonts-on-the-web and everything is working except one step. I successfully created an instance of IDWriteRemoteFontFileLoader (which inherit from IDWriteFontFileLoader), now i have to register it (step 4) using IDWriteFactory.RegisterFontFileLoader which require an IDWriteFontFileLoader as param. Should work if I pass the instance IDWriteRemoteFontFileLoader but, instead, I receive an invalid cast exception.

I don't know if I'm doing something wrong or there is a bug

Thanks

[smourier]

Hi,

Do you have any code to show? Also .NET's invalid cast exception can sometime find its origin in an underlying E_NOINTERFACE COM error, which can be a threading issue (not using an object in the same thread where it was created)

[miquik]

Here's my minimal code that reproduce that error

  using (var coref = DWriteFunctions.DWriteCreateFactory<IDWriteFactory7>())
  {
      hr = coref.Object.CreateHttpFontFileLoader(null, null, out IDWriteRemoteFontFileLoader newLoader);
      hr = coref.Object.RegisterFontFileLoader(newLoader);
      // do something
  }

This gives me invalid cast exception

[smourier]

This is very strange. I have no idea why it fails. It seems internal to .NET. I've checked the interface guids and definition dozen times and I don't see any issue...

What you can test is something like this:

  using (var coref = DWriteFunctions.DWriteCreateFactory<IDWriteFactory7>())
  {
      hr = coref.Object.CreateHttpFontFileLoader(null, null, out IDWriteRemoteFontFileLoader newLoader);

      var wrapper = new Wrapper(newLoader);
      hr = coref.Object.RegisterFontFileLoader(wrapper);
      // do something
  }

class Wrapper : IDWriteFontFileLoader
{
    private IDWriteRemoteFontFileLoader _loader;

    public Wrapper(IDWriteRemoteFontFileLoader loader)
    {
        _loader = loader;
    }

    public HRESULT CreateStreamFromKey(IntPtr fontFileReferenceKey, uint fontFileReferenceKeySize, out IDWriteFontFileStream fontFileStream)
    {
        return _loader.CreateStreamFromKey(fontFileReferenceKey, fontFileReferenceKeySize, out fontFileStream);
    }
}

see if it works around the issue.

[miquik]

Your workaround seems to work; at least I can execute RegisterFontFileLoader without exception. I also try IDWriteInMemoryFontFileLoader interface and it also works. Maybe there is some internal error in IDWriteRemoteFontFileLoader. I ends up I have probably to implement my own custom RemoteFontLoader

Thanks