有没有办法以编程方式确定字体文件是否具有特定的 Unicode 字形？

我正在开发一个生成 PDF 的项目，其中可以包含相当复杂的数学和科学公式。文本以 Times New Roman 格式呈现，它具有相当不错的 Unicode 覆盖率，但并不完整。我们有一个系统可以用更完整的 Unicode 字体来替换 TNR 中没有字形的代码点（就像大多数“陌生”数学符号），但我似乎找不到查询的方法*.ttf 文件以查看给定字形是否存在。到目前为止，我只是硬编码了一个包含代码点的查找表，但我更喜欢自动解决方案。

我在 ASP.net 下的 Web 系统中使用 VB.Net，但任何编程语言/环境中的解决方案将不胜感激。

编辑：win32 解决方案看起来很棒，但我试图解决的具体情况是在 ASP.Net Web 系统中。有没有办法在不将 Windows API DLL 包含到我的网站中的情况下执行此操作？

这是使用 C# 和 Windows API 的一个过程。

[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;
}

然后，给定一个 char 来检查您想要检查的字符和一个 Font 字体来测试它......

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

使用 VB.Net 的相同代码

<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