C++ - How to simulate double click on screen

void DoubleClick(int x, int y)
{
    const double XSCALEFACTOR = 65535 / (GetSystemMetrics(SM_CXSCREEN) - 1);
    const double YSCALEFACTOR = 65535 / (GetSystemMetrics(SM_CYSCREEN) - 1);

    POINT cursorPos;
    GetCursorPos(&cursorPos);

    double cx = cursorPos.x * XSCALEFACTOR;
    double cy = cursorPos.y * YSCALEFACTOR;

    double nx = x * XSCALEFACTOR;
    double ny = y * YSCALEFACTOR;

    INPUT Input={0};
    Input.type = INPUT_MOUSE;

    Input.mi.dx = (LONG)nx;
    Input.mi.dy = (LONG)ny;

    Input.mi.dwFlags = MOUSEEVENTF_MOVE | MOUSEEVENTF_ABSOLUTE | MOUSEEVENTF_LEFTDOWN | MOUSEEVENTF_LEFTUP;

    SendInput(1,&Input,sizeof(INPUT));
    SendInput(1,&Input,sizeof(INPUT));

    Input.mi.dx = (LONG)cx;
    Input.mi.dy = (LONG)cy;

    Input.mi.dwFlags = MOUSEEVENTF_MOVE | MOUSEEVENTF_ABSOLUTE;

    SendInput(1,&Input,sizeof(INPUT));
}
You can use GetWindowRect() to get the window position from its handle and pass relative x and yto DoubleClick function:
RECT rect;
GetWindowRect(hwnd, &rect);

HWND phwnd = GetForegroundWindow();

SetForegroundWindow(hwnd);

DoubleClick(rect.left + x, rect.top + y);

SetForegroundWindow(phwnd); // To activate previous window