XPS writer fails with .Net 4 / font rendering bug?
We have a WPF application that allows users to enter and style text as they wish. Their text is then transformed to XPS to be inserted in a PDF using ABCPdf.
We have recently switched to .Net 4, and now the XPS generation sometimes generates badly-formed XPS.
The only time when a badly-formed XPS is generated is when the user uses a font that overlaps two characters (such as Sevillana, available on Google Fonts). In .Net 4, the characters overlap, whereas in .Net 3.5, they do not. From another SO question I gather that it's because .Net 4.0 has changed its font rendering engine.
.Net 3.5 :
.Net 4.0 : (note how the "d" and "A" overlap)
It looks like .Net 4 does not take the apostrophe's spacing into account, or even negates it. If I remove the apostrophe, the spacing widens. I have created a simple test project to demonstrate the issue : https://github.com/tbroust-trepia/wpf-4-font-rendering
Our method to save a FlowDocument to XPS is pretty much the same as in creating an XPS Document from a FlowDocument and attach it on the fly (I suspect that the original developer just copy/pasted that code) ; it just saves the XPS to a file instead of in a stream.
The MS tool IsXPS says that a specific node is invalid. As a matter of fact, in Documents\1\Pages\1.fpage, the value of Indices is ;,-16;,84;;;;,30. I can see that "0.-16" is not really a number.
So, I have many questions:
- Why is it happening ? I don't understand how the values are converted into these Indices. I guess that the transformation engine tried to set it to "-0.16" but messed up ?
- Can I modify/check the value of this Indices before it's saved ?
- If I cannot, how can I check afterwards ? I have found a sort of XPS validator here but I don't understand how I can check the Indices value from there. I could do it manually, reading and parsing the XML, but I'm really sure it's not a good idea.
Edit
I have opened a bug at Microsoft, but I don't expect much there. I think I will try to modify the generated XPS. It's dirty but it might work.
While waiting for MS to do whatever they want, I have found a way to fix the broken XPS.
public class XpsFile
{
/// <summary>
/// Regex to validate XPS "indices" property (gotten from ABCPDF)
/// </summary>
private static readonly string IndicesRegex = @"(((\(([1-9][0-9]*)(:([1-9][0-9]*))?\))?([0-9]+))?(,(\+?(([0-9]+(\.[0-9]+)?)|(\.[0-9]+))((e|E)(\-|\+)?[0-9]+)?)?(,((\-|\+)?(([0-9]+(\.[0-9]+)?)|(\.[0-9]+))((e|E)(\-|\+)?[0-9]+)?)?(,((\-|\+)?(([0-9]+(\.[0-9]+)?)|(\.[0-9]+))((e|E)(\-|\+)?[0-9]+)?))?)?)?)(;((\(([1-9][0-9]*)(:([1-9][0-9]*))?\))?([0-9]+))?(,(\+?(([0-9]+(\.[0-9]+)?)|(\.[0-9]+))((e|E)(\-|\+)?[0-9]+)?)?(,((\-|\+)?(([0-9]+(\.[0-9]+)?)|(\.[0-9]+))((e|E)(\-|\+)?[0-9]+)?)?(,((\-|\+)?(([0-9]+(\.[0-9]+)?)|(\.[0-9]+))((e|E)(\-|\+)?[0-9]+)?))?)?)?)*";
/// <summary>
/// Fixes the XPS problems it encounters and knows about
/// </summary>
public static void FixXps(string filePath)
{
// first we'll load the XPS file
using (var currentPackage = Package.Open(filePath, FileMode.Open))
{
var pageUri = new Uri("/Documents/1/Pages/1.fpage", UriKind.Relative);
// check that the file we'll modify exists
if (!currentPackage.PartExists(pageUri))
{
throw new Exception(string.Format("Unable to find first page in XPS {0} - unable to fix this XPS !", filePath));
}
// assume the broken part is in the first page
var firstPage = currentPackage.GetPart(pageUri);
var relationships = firstPage.GetRelationships();
var pageContent = XDocument.Load(firstPage.GetStream());
// then we'll look up each glyph and check if their "Indices" property is valid
XNamespace ns = pageContent.Root.GetDefaultNamespace();
var glyphs = (from g in pageContent.Descendants(ns + "Glyphs")
where g.Attribute("Indices") != null
select g).ToList();
for (var i = 0; i < glyphs.Count(); i ++)
{
glyphs[i] = FixGlyph(glyphs[i]);
}
// remove the current (corrupted) file from the package
currentPackage.DeletePart(pageUri);
// add the new (shiny) file to the package
var newPage = currentPackage.CreatePart(pageUri, "application/vnd.ms-package.xps-fixedpage+xml", CompressionOption.NotCompressed);
using (var ms = new MemoryStream())
{
// we need to remove XML declaration, so we need to use the XmlWriter
var settings = new XmlWriterSettings();
settings.Indent = false;
settings.NewLineChars = string.Empty;
settings.NewLineHandling = NewLineHandling.Replace;
settings.OmitXmlDeclaration = true;
using (var xw = XmlWriter.Create(ms, settings))
{
pageContent.WriteTo(xw);
}
ms.Seek(0, SeekOrigin.Begin);
CopyStream(newPage.GetStream(), ms);
}
// now we need to re-create the relationships between the Page file and the fonts
foreach (var relation in relationships)
{
newPage.CreateRelationship(relation.TargetUri, relation.TargetMode, relation.RelationshipType, relation.Id);
}
}
}
/// <summary>
/// Tries to load the XPS, and returns false if it fails
/// </summary>
public static bool IsValidXps(string filePath)
{
try
{
using (var xpsOld = new XpsDocument(filePath, FileAccess.Read))
{
var unused = xpsOld.GetFixedDocumentSequence();
}
return true;
}
catch (System.Windows.Markup.XamlParseException)
{
return false;
}
}
/// <summary>
/// Writes the whole content of a stream into another
/// </summary>
/// <remarks>
/// http://stackoverflow.com/a/18885954/2354542
/// </remarks>
private static void CopyStream(Stream target, Stream source)
{
const int bufSize = 0x1000;
byte[] buf = new byte[bufSize];
int bytesRead = 0;
while ((bytesRead = source.Read(buf, 0, bufSize)) > 0)
{
target.Write(buf, 0, bytesRead);
}
}
/// <summary>
/// Fixes the glyph, if necessary
/// </summary>
private static XElement FixGlyph(XElement g)
{
var matchAttribute = Regex.Match(g.Attribute("Indices").Value, IndicesRegex);
if (!matchAttribute.Success)
{
return g;
}
var hasProblem = false;
foreach (var token in matchAttribute.Value.Split(";".ToCharArray()))
{
if (token == ",")
{
hasProblem = true;
break;
}
}
if (hasProblem)
{
// the Indices attribute is not well-formed: let's try to fix the one(s) that are wrong
var fixedTokens = new List<string>();
foreach (var token in g.Attribute("Indices").Value.Split(";".ToCharArray()))
{
var newToken = token;
var matchToken = Regex.Match(token, @",(-\d+)");
if (matchToken.Success) // negative number, yay ! it's not allowed :-(
{
newToken = ",0"; // it should be zero, I believe
}
fixedTokens.Add(newToken);
}
g.Attribute("Indices").Value = string.Join(";", fixedTokens);
}
return g;
}
}