Disappearing Characters in XPS

A while back, I mentioned how I was using TIFF files to embed a 3rd party report into XPS content. It was decided that the bitmap was rather jarring when compared to the surrounding beautiful vector elements, so I coded up a solution that leveraged the component's export to XPS feature and converted the XPS FixedPages to Canvases thereby creating XAML for a WPF visual which I deserialized and hosted in the app.

There was a problem though. The first page of the report looked great. Second+ pages were missing characters. It seemed to be consistent within each document.

Fonts in XPS are stored as shared resources. I was taking the first occurrence of any font, say "Arial", and putting it in an in-memory package. I'd update the Xaml of my FixedPages-turned-Canvases to point to the in-memory package for the FontUri rather than using the original resource. Because of the consistency with which this was happening, I could only figure that the font files were being corrupted somehow.

It turned out that this was in fact this case. Each report's "Arial" file was a different size. I skimmed the web for a while and found some vague allusions to XPS optimizing fonts.

Today my coworker pinpointed a likely cause:

XpsSerializationManager.SetFontSubsettingPolicy

This method lets you control exactly what I was describing. It determines if all glyphs from the fonts are preserved or if the unused glyphs are stripped out per page or per document.

Thanks Matt!!