Create subset of a TrueType font file using .NET

Question

I am trying to achieve following things:

1. To create subset of original font file which targets only specific characters
2. After browsing through Google I came across following APIs available:
   • ComputeSubset method of GlyphTypeface class in WPF
   • CreateFontPackage in FontSub.dll
3. Though I am able to create subset a of a font file, I am not sure whether it is targetting the characters which I have specified because when I open that file (double click on file), I see all characters there. How exactly can I validate that? I installed that in c:\windows\fonts, and I am able to type all characters in that font whereas I was expecting it will only show characters which I selected.
4. is there a programmer's reference for TrueType font (TTF) files which help us understand TTF files from a programming perspective?

Answer 1

I've used both methods you mention, the first one is far easier. Here's the code I use:

Imports System.Text.Encoding
Imports System.Collections
Imports System.Windows.Media
Public Class FontManager
    Sub New()
        CreateSubSet("my baloney has a first name", New Uri("C:\Windows\Fonts\impact.ttf"))
    End Sub
    Public Sub CreateSubSet(sourceText As String, fontURI As Uri)
        Dim glyphTypeface As GlyphTypeface = New GlyphTypeface(fontURI)
        Dim Index As Generic.ICollection(Of UShort)
        Index = New Generic.List(Of UShort)
        Dim sourceTextBytes As Byte() = Unicode.GetBytes(sourceText)
        Dim sourceTextChars As Char() = Unicode.GetChars(sourceTextBytes)
        Dim sourceTextCharVal As Integer
        Dim glyphIndex As Integer
        For sourceTextCharPos = 0 To UBound(sourceTextChars)
            sourceTextCharVal = AscW(sourceTextChars(sourceTextCharPos))
            glyphIndex = glyphTypeface.CharacterToGlyphMap(sourceTextCharVal)
            Index.Add(glyphIndex)
        Next
        Dim filebytes() As Byte = glyphTypeface.ComputeSubset(Index)
        Using fileStream As New System.IO.FileStream("C:\Users\Me\Documents\impact-subset.ttf", System.IO.FileMode.Create)
            fileStream.Write(filebytes, 0, filebytes.Length)
        End Using
    End Sub
End Class

Of course for sourceText, you can just send in unique characters if you want.

The link gilamesh mentions is a great place for learning about TTF fonts. The other reference which I've found to be invaluable is http://developer.apple.com/fonts/TTRefMan/RM06/Chap6.html