static void mouse_event(int dwFlags, int dx, int dy, int cButtons, int dwExtraInfo) 
{ 
 int x = dx, y = dy; 
 edit_position(dwFlags, dx, dy, ref x, ref y); 
 IntPtr hWndFromPoint = WindowFromPoint(x, y); 
 screen_to_client(hWndFromPoint, ref x, ref y); 
 send_message(hWndFromPoint, dwFlags, cButtons, x, y); 
} 

static void edit_position(int dwFlags, int dx, int dy, ref int x, ref int y) 
{ 
 Point pos = MousePosition; 
 x = x + pos.X; 
 y = y + pos.Y; 
 if ((dwFlags | MOUSEEVENTF_ABSOLUTE) == dwFlags) 
  SetCursorPos(dx, dy); 
 if ((dwFlags | MOUSEEVENTF_MOVE) == dwFlags) 
  SetCursorPos(x, y); 
} 

static void send_message(IntPtr hWnd, int dwFlags, int cButtons, int x, int y) 
{ 
 if ((dwFlags | MOUSEEVENTF_LEFTDOWN) == dwFlags) 
  SendMessage(hWnd, WM_LBUTTONDOWN, cButtons, MakeDWord(x, y)); 
 if ((dwFlags | MOUSEEVENTF_LEFTUP) == dwFlags) 
  SendMessage(hWnd, WM_LBUTTONUP, cButtons, MakeDWord(x, y)); 
 if ((dwFlags | MOUSEEVENTF_RIGHTDOWN) == dwFlags) 
  SendMessage(hWnd, WM_RBUTTONDOWN, cButtons, MakeDWord(x, y)); 
 if ((dwFlags | MOUSEEVENTF_RIGHTUP) == dwFlags) 
  SendMessage(hWnd, WM_RBUTTONUP, cButtons, MakeDWord(x, y)); 
 if ((dwFlags | MOUSEEVENTF_MIDDLEDOWN) == dwFlags) 
  SendMessage(hWnd, WM_MBUTTONDOWN, cButtons, MakeDWord(x, y)); 
 if ((dwFlags | MOUSEEVENTF_MIDDLEUP) == dwFlags) 
  SendMessage(hWnd, WM_MBUTTONUP, cButtons, MakeDWord(x, y)); 
} 

static int MakeDWord(int low, int high) 
{ 
 return low + (high * Abs(~ushort.MaxValue)); 
} 
static int Abs(int value) 
{ 
 return ((value >> 31) ^ value) - (value >> 31); 
} 
MakeDWord / 合并整数，函数主要是把两个short合并为一个int，分为low、high两部分
 
 
static bool screen_to_client(IntPtr hwnd, ref int x, ref int y) 
{ 
 bool bRetVal = false; 
 Point lpptPos = new Point(x, y); 
 if ((bRetVal = ScreenToClient(hwnd, ref lpptPos))) 
 { 
  x = lpptPos.X; 
  y = lpptPos.Y; 
 } 
 return bRetVal; 
} 
screen_to_client函数故名思意，它主要用于把屏幕上的坐标转换到窗口客户上对应坐标 
public const int WM_LBUTTONDOWN = 513; // 鼠标左键按下 
public const int WM_LBUTTONUP = 514; // 鼠标左键抬起 
public const int WM_RBUTTONDOWN = 516; // 鼠标右键按下 
public const int WM_RBUTTONUP = 517; // 鼠标右键抬起 
public const int WM_MBUTTONDOWN = 519; // 鼠标中键按下 
public const int WM_MBUTTONUP = 520; // 鼠标中键抬起 
public const int MOUSEEVENTF_MOVE = 0x0001; // 移动鼠标   
public const int MOUSEEVENTF_LEFTDOWN = 0x0002; // 鼠标左键按下  
public const int MOUSEEVENTF_LEFTUP = 0x0004; // 鼠标左键抬起  
public const int MOUSEEVENTF_RIGHTDOWN = 0x0008; // 鼠标右键按下  
public const int MOUSEEVENTF_RIGHTUP = 0x0010; // 鼠标右键抬起   
public const int MOUSEEVENTF_MIDDLEDOWN = 0x0020; // 鼠标中键按下 
public const int MOUSEEVENTF_MIDDLEUP = 0x0040; // 鼠标中键抬起   
public const int MOUSEEVENTF_ABSOLUTE = 0x8000; // 绝对坐标 


[DllImport("user32.dll", SetLastError = true)] 
public static extern int SendMessage(IntPtr hWnd, int uMsg, int wParam, int lParam); 
[DllImport("user32.dll", SetLastError = true)] 
public static extern IntPtr WindowFromPoint(int xPoint, int yPoint); 
[DllImport("user32.dll", SetLastError = true)] 
public static extern int SetCursorPos(int x, int y); 
[DllImport("user32.dll", SetLastError = true)] 
public static extern bool ScreenToClient(IntPtr hWnd, ref Point lppt); 
// [DllImport("user32", SetLastError = true)] 
// public static extern int mouse_event(int dwFlags, int dx, int dy, int cButtons, int dwExtraInfo);