Is there a way to programmatically determine if a font file has a specific Unicode Glyph?

Question

I'm working on a project that generates PDFs that can contain fairly complex math and science formulas. The text is rendered in Times New Roman, which has pretty good Unicode coverage, but not complete. We have a system in place to swap in a more Unicode complete font for code points that don't have a glyph in TNR (like most of the "stranger" math symbols,) but I can't seem to find a way to query the *.ttf file to see if a given glyph is present. So far, I've just hard-coded a lookup table of which code points are present, but I'd much prefer an automatic solution.

I'm using VB.Net in a web system under ASP.net, but solutions in any programming language/environment would be appreciated.

Edit: The win32 solution looks excellent, but the specific case I'm trying to solve is in an ASP.Net web system. Is there a way to do this without including the windows API DLLs into my web site?

Answer 1

Here's a pass at it using c# and the windows API.

[DllImport("gdi32.dll")] public static extern uint GetFontUnicodeRanges(IntPtr hdc, IntPtr lpgs);  [DllImport("gdi32.dll")] public extern static IntPtr SelectObject(IntPtr hDC, IntPtr hObject);  public struct FontRange {     public UInt16 Low;     public UInt16 High; }  public List<FontRange> GetUnicodeRangesForFont(Font font) {     Graphics g = Graphics.FromHwnd(IntPtr.Zero);     IntPtr hdc = g.GetHdc();     IntPtr hFont = font.ToHfont();     IntPtr old = SelectObject(hdc, hFont);     uint size = GetFontUnicodeRanges(hdc, IntPtr.Zero);     IntPtr glyphSet = Marshal.AllocHGlobal((int)size);     GetFontUnicodeRanges(hdc, glyphSet);     List<FontRange> fontRanges = new List<FontRange>();     int count = Marshal.ReadInt32(glyphSet, 12);     for (int i = 0; i < count; i++)     {         FontRange range = new FontRange();         range.Low = (UInt16)Marshal.ReadInt16(glyphSet, 16 + i * 4);         range.High = (UInt16)(range.Low + Marshal.ReadInt16(glyphSet, 18 + i * 4) - 1);         fontRanges.Add(range);     }     SelectObject(hdc, old);     Marshal.FreeHGlobal(glyphSet);     g.ReleaseHdc(hdc);     g.Dispose();     return fontRanges; }  public bool CheckIfCharInFont(char character, Font font) {     UInt16 intval = Convert.ToUInt16(character);     List<FontRange> ranges = GetUnicodeRangesForFont(font);     bool isCharacterPresent = false;     foreach (FontRange range in ranges)     {         if (intval >= range.Low && intval <= range.High)         {             isCharacterPresent = true;             break;         }     }     return isCharacterPresent; } 

Then, given a char toCheck that you want to check and a Font theFont to test it against...

if (!CheckIfCharInFont(toCheck, theFont) {     // not present } 

Same code using VB.Net

<DllImport("gdi32.dll")> _ Public Shared Function GetFontUnicodeRanges(ByVal hds As IntPtr, ByVal lpgs As IntPtr) As UInteger End Function    <DllImport("gdi32.dll")> _ Public Shared Function SelectObject(ByVal hDc As IntPtr, ByVal hObject As IntPtr) As IntPtr End Function    Public Structure FontRange     Public Low As UInt16     Public High As UInt16 End Structure    Public Function GetUnicodeRangesForFont(ByVal font As Font) As List(Of FontRange)     Dim g As Graphics     Dim hdc, hFont, old, glyphSet As IntPtr     Dim size As UInteger     Dim fontRanges As List(Of FontRange)     Dim count As Integer      g = Graphics.FromHwnd(IntPtr.Zero)     hdc = g.GetHdc()     hFont = font.ToHfont()     old = SelectObject(hdc, hFont)     size = GetFontUnicodeRanges(hdc, IntPtr.Zero)     glyphSet = Marshal.AllocHGlobal(CInt(size))     GetFontUnicodeRanges(hdc, glyphSet)     fontRanges = New List(Of FontRange)     count = Marshal.ReadInt32(glyphSet, 12)      For i = 0 To count - 1         Dim range As FontRange = New FontRange         range.Low = Marshal.ReadInt16(glyphSet, 16 + (i * 4))         range.High = range.Low + Marshal.ReadInt16(glyphSet, 18 + (i * 4)) - 1         fontRanges.Add(range)     Next      SelectObject(hdc, old)     Marshal.FreeHGlobal(glyphSet)     g.ReleaseHdc(hdc)     g.Dispose()      Return fontRanges End Function    Public Function CheckIfCharInFont(ByVal character As Char, ByVal font As Font) As Boolean     Dim intval As UInt16 = Convert.ToUInt16(character)     Dim ranges As List(Of FontRange) = GetUnicodeRangesForFont(font)     Dim isCharacterPresent As Boolean = False      For Each range In ranges         If intval >= range.Low And intval <= range.High Then             isCharacterPresent = True             Exit For         End If     Next range     Return isCharacterPresent End Function   

Answer 2

Scott's answer is good. Here is another approach that is probably faster if checking just a couple of strings per font (in our case 1 string per font). But probably slower if you are using one font to check a ton of text.

    [DllImport("gdi32.dll", EntryPoint = "CreateDC", CharSet = CharSet.Auto, SetLastError = true)]     private static extern IntPtr CreateDC(string lpszDriver, string lpszDeviceName, string lpszOutput, IntPtr devMode);      [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]     private static extern bool DeleteDC(IntPtr hdc);      [DllImport("Gdi32.dll")]     private static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);      [DllImport("Gdi32.dll", CharSet = CharSet.Unicode)]     private static extern int GetGlyphIndices(IntPtr hdc, [MarshalAs(UnmanagedType.LPWStr)] string lpstr, int c,                                               Int16[] pgi, int fl);      /// <summary>     /// Returns true if the passed in string can be displayed using the passed in fontname. It checks the font to      /// see if it has glyphs for all the chars in the string.     /// </summary>     /// <param name="fontName">The name of the font to check.</param>     /// <param name="text">The text to check for glyphs of.</param>     /// <returns></returns>     public static bool CanDisplayString(string fontName, string text)     {         try         {             IntPtr hdc = CreateDC("DISPLAY", null, null, IntPtr.Zero);             if (hdc != IntPtr.Zero)             {                 using (Font font = new Font(new FontFamily(fontName), 12, FontStyle.Regular, GraphicsUnit.Point))                 {                     SelectObject(hdc, font.ToHfont());                     int count = text.Length;                     Int16[] rtcode = new Int16[count];                     GetGlyphIndices(hdc, text, count, rtcode, 0xffff);                     DeleteDC(hdc);                      foreach (Int16 code in rtcode)                         if (code == 0)                             return false;                 }             }         }         catch (Exception)         {             // nada - return true             Trap.trap();         }         return true;     }