Since the public release of Microsoft Silverlight 2, I've gotten a few internal and external requests to migrate my SimpleSilverlightXpsViewer sample application to the final Silverlight bits. (Background reading: Introductory Post for the Alpha, Beta 1 Update, Beta 2 Update, Interesting Scenario.) Unfortunately, there is a pretty significant roadblock preventing this and I'm afraid I don't have a good solution. :(

Specifically, the "BreakingChangesBetweenBeta2andRelease" document contains the following item:

Font URI is Restricted to Assembly Resource

Who Is Affected:
Silverlight 2 Beta1 or Beta 2 applications (not Silverlight 1.0 applications) that reference fonts (or zip of fonts) via the URI syntax in the Control.FontFamily, TextBlock.FontFamily or Glyphs.FontUri attributes and where the fonts are not embedded within the assembly (dll) of the control or application.
Fix Required:
You can specify a font (or in some cases a zip of fonts) in URI format via the Control.FontFamily, TextBlock.FontFamily and the Glyphs.FontUri attributes. If you are, you will need to ensure your font is marked as a "resource" in the project system.

This is problematic for SimpleSilverlightXpsViewer because it uses Glyphs.FontUri to associate the font for the on-screen text with the corresponding ODTTF font file in the XPS document - and it's impossible for a general-purpose document viewer to have all the fonts in the world compiled into its own assembly. Making matters worse, fonts in an XPS document are identified by GUID, so it doesn't even seem possible to embed the N most common fonts and try to cover the 90% scenario by looking at font names and using the best available match. The seemingly obvious alternative is to use the FontSource property instead - but that's not exposed by the Glyphs class. The only workable option I see is to embed a single font in the viewer's resources and use that ONE font for ALL fonts in every XPS file. Obviously, this puts a pretty big damper on the idea of displaying an arbitrary XPS document how it was meant to be displayed because all the font fidelity of the original document is lost.

In controlled scenarios, it should still be possible to bundle an XPS document and its fonts in a compiled assembly and point some suitably modified version of SimpleSilverlightXpsViewer at that - but by then it's no longer as much of a client-side XPS viewer as it is a client+server document viewing solution (that could use straight XAML when you get down to it!). Unfortunately, my original vision of a Silverlight-based XPS viewer that lets users open any arbitrary XPS file on their computer or on the web is going to have to wait a little while longer to be realized. :(

In case folks are wondering, I did ask why this restriction is present. As I understand things (caveat: I am not a lawyer or a spokesperson for Microsoft), some fonts have copyrights and/or licensing restrictions placed on them by their creator and some of those fonts should not be made available via HTTP (where everybody can access them freely). I may not be happy about the consequences of this for SimpleSilverlightXpsViewer, but I understand why this restriction makes sense.

So to make a long story short: I have not yet come up with a good way to migrate SimpleSilverlightXpsViewer to Silverlight 2 and I apologize to all the folks who have expressed interest in this sample. For what it's worth, if I ever come up with a solution I like, I'll immediately update SimpleSilverlightXpsViewer and post the details! :)