NativeMethods.cs

using System;
using System.Runtime.InteropServices;

namespace HoverText
{
  internal static class NativeMethods
  {
    // ---------- Cursor position ----------

    [StructLayout(LayoutKind.Sequential)]
    public struct POINT
    {
      public int X;
      public int Y;
    }

    [DllImport("user32.dll")]
    public static extern bool GetCursorPos(out POINT lpPoint);

    // ---------- Low-level keyboard hook ----------

    public const int WH_KEYBOARD_LL = 13;
    public const int WM_KEYDOWN = 0x0100;
    public const int WM_KEYUP = 0x0101;
    public const int WM_SYSKEYDOWN = 0x0104;
    public const int WM_SYSKEYUP = 0x0105;

    [StructLayout(LayoutKind.Sequential)]
    public struct KBDLLHOOKSTRUCT
    {
      public int vkCode;
      public int scanCode;
      public int flags;
      public int time;
      public IntPtr dwExtraInfo;
    }

    public delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr SetWindowsHookEx(int idHook, LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);

    [DllImport("user32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool UnhookWindowsHookEx(IntPtr hhk);

    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll")]
    public static extern short GetAsyncKeyState(int vKey);

    [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    public static extern IntPtr GetModuleHandle(string lpModuleName);

    // ---------- Key names / capture ----------

    // Reserved while recording a trigger: Enter finishes, Esc cancels.
    public const int VK_RETURN = 0x0D;
    public const int VK_ESCAPE = 0x1B;
    public const int VK_PACKET = 0xE7;

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern uint MapVirtualKey(uint uCode, uint uMapType);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern int GetKeyNameText(IntPtr lParam, System.Text.StringBuilder lpString, int cchSize);

    /// <summary>
    /// Friendly, localized name for a virtual key code (e.g. "Ctrl",
    /// "A", "Page Up"). Modifier keys get clean names regardless of side.
    /// </summary>
    public static string KeyName(int vkCode)
    {
      return vkCode switch
      {
        0xA0 or 0xA1 => "Shift",
        0xA2 or 0xA3 => "Ctrl",
        0xA4 or 0xA5 => "Alt",
        0x5B or 0x5C => "Win",
        _ => MapKeyName(vkCode)
      };
    }

    private static string MapKeyName(int vkCode)
    {
      uint scan = MapVirtualKey((uint)vkCode, 0);
      // lParam layout: scan code in bits 16-23, extended flag in bit 24.
      var lParam = new IntPtr((long)(scan << 16) | 0x01000000);
      var sb = new System.Text.StringBuilder(64);
      if (GetKeyNameText(lParam, sb, sb.Capacity) > 0)
        return sb.ToString();
      return $"VK {vkCode}";
    }

    // ---------- Click-through / tool-window styles for the overlay ----------

    public const int GWL_EXSTYLE = -20;
    public const int WS_EX_LAYERED = 0x80000;
    public const int WS_EX_TRANSPARENT = 0x20;
    public const int WS_EX_TOOLWINDOW = 0x80;
    public const int WS_EX_NOACTIVATE = 0x08000000;

    [DllImport("user32.dll", EntryPoint = "GetWindowLong")]
    private static extern int GetWindowLong32(IntPtr hWnd, int nIndex);

    [DllImport("user32.dll", EntryPoint = "SetWindowLong")]
    private static extern int SetWindowLong32(IntPtr hWnd, int nIndex, int dwNewLong);

    [DllImport("user32.dll", EntryPoint = "GetWindowLongPtr")]
    private static extern IntPtr GetWindowLongPtr64(IntPtr hWnd, int nIndex);

    [DllImport("user32.dll", EntryPoint = "SetWindowLongPtr")]
    private static extern IntPtr SetWindowLongPtr64(IntPtr hWnd, int nIndex, IntPtr dwNewLong);

    // 32/64-bit safe wrappers (GetWindowLongPtr only exists on 64-bit user32).
    public static IntPtr GetWindowLongPtr(IntPtr hWnd, int nIndex)
    {
      return IntPtr.Size == 8
          ? GetWindowLongPtr64(hWnd, nIndex)
          : new IntPtr(GetWindowLong32(hWnd, nIndex));
    }

    public static IntPtr SetWindowLongPtr(IntPtr hWnd, int nIndex, IntPtr dwNewLong)
    {
      return IntPtr.Size == 8
          ? SetWindowLongPtr64(hWnd, nIndex, dwNewLong)
          : new IntPtr(SetWindowLong32(hWnd, nIndex, dwNewLong.ToInt32()));
    }
  }
}