‘XamlUIPresenter’ , what are you ? :)

There is an interesting API in the WinRT XAML namespace that sounds damn interesting BUT no public examples of how to use it. Even the MS folks are quiet about it ..

What does “XamlUIPresenter” do?

XamlUIPresenter

The documentation explains it as such …

reference : msdn

A xaml visual tree on a D3D surface ?! Seriously that is some awesome sauce right there. I can’t begin to tell you how excited that one sentence makes me

Problem is how do you use it, and is it even working ?!

Blend 5

All Google or Bing searches for the term ‘XamlUIPresenter’ leads back to the msdn page, no examples or demos at all. There’s a conspiracy to hide this api from us, I’m sure of it !!!

Anyway by chance in my normal day to day reflecting of all things that i find interesting, i chanced upon it’s use in Blend 5 for Metro Apps .. !!!!

Let me explain how they use it ….

Blend Design Surface – Artboard

If you don’t already know Blend and Visual Studio share the same design surface rendering engine.

In the world of Expression Blend the design surface is an “DeviceViewArtboard” which is itself an “Artboard” which itself is just a xaml “Control” . Remember Blend is after all a XAML (WPF) app.

A Silverlight App in Blend is rendered on the design surface using the “SilverlightArtboard” which is an “Artboard” (note it doesn’t derive from DeviceViewArtboard)

A WPF App in Blend is rendered through a weird way which I believe is legacy, it hasn’t been re-written with the Artboard approach, if your interested use reflector to see how its done otherwise I won’t cover it here

[use reflector to see how WPF renders to the design surface artboard]

A Metro HTML app in Blend is rendered on a design surface using the “HtmlAartboard” which is “DeviceViewArtboard”

A Metro XAML app in Blend is rendered on a design surface using the “WindowsUIXamlAartboard” which is also a “DeviceViewArtboard”

Simply put the relationship looks like this for the 3 different rendering types of Silverlight apps, HTML Metro apps, XAML Metro apps.

I am only going to concentrate on the XAML Metro app side of things from this point onwards …

an Artboard’s “ImageHost”

Without getting into too much detail each “Artboard” contains an “ImageHost”, which as the name suggests is the host of an image, how that image is created is what interests me

In the case of the WindowsUIXamlArtboard the image host is a class of type “XamlImageHost”

And if you trace it through the actual instance that is assigned to the ImageHost is a class called “WindowsUIXamlImageHost” that is found in the Microsoft.Expression.WindowsXamlPlatform.dll .

I should point out that each of the different development platforms has it’s own “Platform” dll and the dll’s normally follow a common layout & resource pattern.

Everything we want to know is found in the WindowsXamlPlatform …

Now when you look at WindowsUIXamlImageHost in the WindowsXamlPlatform dll there is a presenterWrapper property.

And this PresenterWrapper class happens to sit in the same namespace…

Two very interesting things in this class ….

1. this class references “Windows.UI.Xaml”

2. this class PInvokes the “CreateXamlUIPresenter” call from Windows.UI.Xaml.dll

I think we found ourselves code that uses the XamlUIPresenter

Blend uses XamlUIPresenter ?!

As it turns out Blend, for XAML Metro apps, uses the XamlUIPresenter API in WinRT to render a visual tree on a Direct3D surface which intern is displayed in the artboard in the designer

Not 100% sure about this BUT it appears that the PresenterWrapper.RootVisual contains the xaml visual tree that will be rendered in a D3D surface

The PresentSiteWrapper wraps up all the logic to make the interop calls between managed/native for rendering surfaces handle pointers etc.

Here’s the PresentSiteWrapper interface incase your interested

So it does a bunch of native calls to pass thru the visual tree and return back the D3D surface which in turn is turned into BitmapData for rendering in the artboard.

Conclusion

This XamlUIPresenter api is damn interesting and if it does what i think it does is very very useful. Rendering a Xaml metro app in a “window” in the desktop looks possible from where I’m sitting.

Now that I know how it works and the basic plumbing it needs next step is to try to use it to render Xaml visual trees on a Direct3D surface from within a metro app. I really want to be able to take a visual tree and render to the GPU as is, then possibly print that tree ?!   A future post will explore this!

In Silverlight we can output a visual tree to the WriteableBitmap for printing and doing cool things with, could we do the same with XamlUIPresenter ?!

Maybe this api is intentionally undefined because MS is still working out the story around it. …