C# Definition:

delegate int DTT_CALLBACK_PROC(IntPtr hdc, [MarshalAs(UnmanagedType.LPWStr)] string text, int textLen, ref RECT rc, int flags, IntPtr lParam);

[StructLayout(LayoutKind.Sequential)]
struct DTTOPTS
{
    public int dwSize;
    public DTT dwFlags;
    public int crText;
    public int crBorder;
    public int crShadow;
    public TEXTSHADOWTYPE iTextShadowType;
    public System.Drawing.Point ptShadowOffset;
    public uint dwFlags;
    public COLORREF crText;
    public COLORREF crBorder;
    public COLORREF crShadow;
    public int iTextShadowType;
    public POINT ptShadowOffset;
    public int iBorderSize;
    public int iFontPropId;
    public int iColorPropId;
    public int iStateId;
    [MarshalAs(UnmanagedType.Bool)]
    public bool fApplyOverlay;
    public int iGlowSize;
    [MarshalAs(UnmanagedType.FunctionPtr)]
    public DTT_CALLBACK_PROC pfnDrawTextCallback;
    public IntPtr lParam;
}

VB Definition:

Structure DTTOPTS
Public TODO
End Structure

User-Defined Field Types:

DTT, TEXTSHADOWTYPE

Alternate C# Definition

public delegate int DrawThemeTextCallback(IntPtr hdc, [MarshalAs(UnmanagedType.LPWStr)] string text, int textLen, ref RECT rc, int flags, IntPtr lParam);

[StructLayout(LayoutKind.Sequential)]
public struct DrawThemeTextOptions
{
   private int dwSize;
   private DrawThemeTextOptionsFlags dwFlags;
   private int crText;
   private int crBorder;
   private int crShadow;
   private TextShadowType iTextShadowType;
   private System.Drawing.Point ptShadowOffset;
   private int iBorderSize;
   private int iFontPropId;
   private int iColorPropId;
   private int iStateId;
   [MarshalAs(UnmanagedType.Bool)]
   private bool fApplyOverlay;
   private int iGlowSize;
   [MarshalAs(UnmanagedType.FunctionPtr)]
   private DrawThemeTextCallback pfnDrawTextCallback;
   private IntPtr lParam;

   public DrawThemeTextOptions(bool init) : this()
   {
     dwSize = Marshal.SizeOf(typeof(DrawThemeTextOptions));
   }

   public Color AlternateColor
   {
     get { return ColorTranslator.FromWin32(iColorPropId); }
     set
     {
       iColorPropId = ColorTranslator.ToWin32(value);
       dwFlags |= DrawThemeTextOptionsFlags.ColorProp;
     }
   }

   public DrawThemeTextSystemFonts AlternateFont
   {
     get { return (DrawThemeTextSystemFonts)iFontPropId; }
     set
     {
       iFontPropId = (int)value;
       dwFlags |= DrawThemeTextOptionsFlags.FontProp;
     }
   }

   public bool AntiAliasedAlpha
   {
     get { return (dwFlags & DrawThemeTextOptionsFlags.Composited) == DrawThemeTextOptionsFlags.Composited; }
     set { SetFlag(DrawThemeTextOptionsFlags.Composited, value); }
   }

   public bool ApplyOverlay
   {
     get { return fApplyOverlay; }
     set
     {
       fApplyOverlay = value;
       dwFlags |= DrawThemeTextOptionsFlags.ApplyOverlay;
     }
   }

   public Color BorderColor
   {
     get { return ColorTranslator.FromWin32(crBorder); }
     set
     {
       crBorder = ColorTranslator.ToWin32(value);
       dwFlags |= DrawThemeTextOptionsFlags.BorderColor;
     }
   }

   public int BorderSize
   {
     get { return iBorderSize; }
     set
     {
       iBorderSize = value;
       dwFlags |= DrawThemeTextOptionsFlags.BorderSize;
     }
   }

   public DrawThemeTextCallback Callback
   {
     get { return pfnDrawTextCallback; }
     set
     {
       pfnDrawTextCallback = value;
       dwFlags |= DrawThemeTextOptionsFlags.Callback;
     }
   }

   public int GlowSize
   {
     get { return iGlowSize; }
     set
     {
       iGlowSize = value;
       dwFlags |= DrawThemeTextOptionsFlags.GlowSize;
     }
   }

   public IntPtr LParam
   {
     get { return lParam; }
     set { lParam = value; }
   }

   public bool ReturnCalculatedRectangle
   {
     get { return (dwFlags & DrawThemeTextOptionsFlags.CalcRect) == DrawThemeTextOptionsFlags.CalcRect; }
     set { SetFlag(DrawThemeTextOptionsFlags.CalcRect, value); }
   }

   public Color ShadowColor
   {
     get { return ColorTranslator.FromWin32(crShadow); }
     set
     {
       crShadow = ColorTranslator.ToWin32(value);
       dwFlags |= DrawThemeTextOptionsFlags.ShadowColor;
     }
   }

   public Point ShadowOffset
   {
     get { return new Point(ptShadowOffset.X, ptShadowOffset.Y); }
     set
     {
       ptShadowOffset = value;
       dwFlags |= DrawThemeTextOptionsFlags.ShadowOffset;
     }
   }

   public TextShadowType ShadowType
   {
     get { return iTextShadowType; }
     set
     {
       iTextShadowType = value;
       dwFlags |= DrawThemeTextOptionsFlags.ShadowType;
     }
   }

   public Color TextColor
   {
     get { return ColorTranslator.FromWin32(crText); }
     set
     {
       crText = ColorTranslator.ToWin32(value);
       dwFlags |= DrawThemeTextOptionsFlags.TextColor;
     }
   }

   private void SetFlag(DrawThemeTextOptionsFlags f, bool value)
   {
     if (value)
       dwFlags |= f;
     else
       dwFlags &= ~f;
   }
}