Has Airspace Support Definitely Been Dropped in WPF 4.5?

There is a rather good blog post from Dwayne Need that describes the extraordinary effort they put in trying to make it work. Nothing subtle, they for example ending up intercepting over 200 GDI functions to get them to play along with the WPF rendering model. The outcome was to be expected:

You can imaging my heartbreak when, after an extensive review, we decided we could not actually ship this feature. Our concern was that we had to hack too deeply into the system, and in ways that were too difficult to explain - let alone maintain. Even though we required that developers explicitly turn on this feature for each HwndHost, we felt the kinds of problems they would encounter would be baffling to them and training our support engineers to handle the escalations would be very difficult. Even towards the end of our development, we were struggling with a long bug tail and performance concerns.

This is exactly the kind of deep system integration that needs to be done by the Win32 platform team, officially sanctioned and supported. With Win8, we are beginning to see some incremental improvements in this space, as noted before in the DirectComposition API. Unfortunately, it is still not possible to build the same kind of rich composited experience we had developed.

Whether the Windows group is going to commit to providing this kind of integration is right now an open question. They certainly put their money on a very different horse and spent a lot of effort on WinRT, a rendering model that's certainly inspired by WPF but doesn't do anything to make it better. If it is going to be tackled at all then count on years to get there.

Do check the rest of the blog post as well. It has excellent, albeit it high-level, advice on addressing existing airspace issues.

A suggestion to "Bring back the HwndHost.IsRedirected and CompositionMode" was posted at the Visual Studio UserVoice.

Microsoft declined it, saying:

at this time, we will not be able to add the feature to WPF and the .NET Framework.

It also looks like the MSDN pages you linked to have been taken down.