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§ Avalon remoting is now a whole lot less attractive

Windows Presentation Foundation (WPF) has an interesting feature called Remoting where it is able to render primitives over Remote Desktop by sending primitives over the network instead of raw bits. While I believe this already happened in XP for some GDI primitives, as far as I know this is the only way to send hardware accelerated 3D across the wire, since regular Direct3D rendering gets remoted at the bitmap level instead of the primitive level. Well, according to a blog post from a WPF member (http://blogs.msdn.com/jgoldb/archive/2008/05/15/what-s-new-for-performance-in-wpf-in-net-3-5-sp1.aspx), this got neutered not too long ago:

Remoting

Although we have not improved this scenario, it is important to highlight some differences related to Remoting
On .Net Framework 3.0 and .Net Framework 3.5:

  • Vista to Vista with DWM on, we Remoted content as Primitives (e.g. the channel protocol went over the network) (This is for the Remote Desktop case only, not Terminal Server)
  • In other cases: we Remoted content as Bitmaps

On .Net Framework 3.5 SP1

  • We now remote as bitmaps in ALL cases.
  • The reason is that WPF 3.5 SP1 now uses a new graphics DLL (wpfgfx.dll) and certain changes could not be made to Vistaís existing graphics DLL (milcore.dll) that is also used by DWM.
  • Although this could be seen a regression at first, depending on the complexity of the application scene (e.g. very rich scenes) this can actually improve performance in certain scenarios . Also, connections with reasonably high bandwidth and scenarios that donít involve a lot of animation or 3D, for instance, tend to remote just fine via bitmaps.

Ouch. I haven't looked into this deeply, but if I interpret this correctly, this means that the remoting advantage of WPF is effectively gone with .NET 3.5 SP1, because WPF apps are now going to be remoted just like any other app that's using a rendering method other than GDI, i.e. as an image. The comment about wpfgfx.dll vs. milcore.dll also implies that there isn't much, if any, advantage that WPF gives you over Direct3D API-wise. For a while I was wondering if it would be worth trying hacks to get WPF or at least MILCORE usable from native code without having to spin up the CLR, but this is looking increasingly less useful since I already have a reasonably powerful Direct3D9 layer and an image resampler that is probably faster than WPF's new shader JIT. Not to mention that, unless it's been added since the original API, WPF's support for offscreen rendering is a bit lacking.

I do wonder about the pixel shader JIT, though... as usual I take any claims about speed from Microsoft with skepticism, but on the other hand, it can't possibly be any slower than refrast. Anyone played around with the new JITter? Show me the assembly. :)

Comments

Comments posted:


Software is getting faster slower than hardware faster.

Murmel - 07 08 08 - 12:38


Maybe the basic problem is in detecting what .NET version the client is running. Vista to Vista was easy -- that's why it only worked with Vista, not with .NET 3.0 on XP. There's some kind of new security protocol involved with Vista remote desktop that, if you remote desktop to a non-Vista machine, it warns you about. I assume that the milcore layer is somehow notified about this security issue. I'm guessing that's as granular as they can get, so the ability to tell that a remote desktop client has 3.5 SP1 might be impossible. This is all speculation of course, but based on their description it makes sense -- probably to be fixed in Windows 7.

Trimbo (link) - 07 08 08 - 22:56


I don't think so -- AFAIK .NET isn't involved with the remote desktop support and that part's fully in native code. I think originally the .NET part of WPF just handled UI hierarchy and packing the render commands into streams to pass to the native milcore layer, although apparently a lot of what used to be done in milcore is now done in wpfgfx.dll. Like the old MSVCRT.DLL, I guess what happened is that milcore got integrated into the OS, and then the team that was using it discovered that it became a boat anchor given the glacial rate at which the OS is revved.

The MIL part of MILCORE stands for Media Integration Layer, btw, and I'm pretty sure it doesn't handle any RDP authentication or have anything to do with the authentication warning. I don't know how Avalon remoting works over the Terminal Services connection, although I suspect that it's embedded in the base video support itself. Terminal Services does have a way to add plugin DLLs and open virtual channels over the wire, but I don't know how the integration works or whether it can be made as seamless as the WDDM 3D redirection in Vista. If it could, it'd be cool to throw in a fast JPEG compression mode.

Side note, I use the 6.0 version of the Remote Desktop client even when connecting to XP systems because it lets you type in the login info locally instead of having to do it over the remote connection.

Phaeron - 08 08 08 - 03:11

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