...
else if (byCodeOption == 1)
{
    #define ABSOLUTE_XY_MAX 65535

    INPUT input={0};
    // left movement
    int screenX = GetSystemMetrics(SM_CXSCREEN);
    int screenY = GetSystemMetrics(SM_CYSCREEN);
    input.type = INPUT_MOUSE;
    input.mi.dwFlags = MOUSEEVENTF_MOVE | MOUSEEVENTF_ABSOLUTE; // mouse movement
    input.mi.dx = pt.x * (ABSOLUTE_XY_MAX / screenX); input.mi.dy = pt.y * (ABSOLUTE_XY_MAX / screenY);
    SendInput(1, &input, sizeof(INPUT));
    Sleep(1);
    // left down
    ZeroMemory(&input,sizeof(INPUT)); //clear out input
    input.type = INPUT_MOUSE;
    input.mi.dwFlags = MOUSEEVENTF_LEFTDOWN; // mouse button down
    SendInput(1,&input,sizeof(INPUT));
    Sleep(1);
    // left up
    ZeroMemory(&input,sizeof(INPUT)); //clear out input
    input.type = INPUT_MOUSE;
    input.mi.dwFlags = MOUSEEVENTF_LEFTUP; // mouse button up
    SendInput(1,&input,sizeof(INPUT));
}

C>...
C>else if (byCodeOption == 1)
C>{
C>    #define ABSOLUTE_XY_MAX 65535

C>    INPUT input={0};
C>    // left movement
C>    int screenX = GetSystemMetrics(SM_CXSCREEN);
C>    int screenY = GetSystemMetrics(SM_CYSCREEN);
C>    input.type = INPUT_MOUSE;
C>    input.mi.dwFlags = MOUSEEVENTF_MOVE | MOUSEEVENTF_ABSOLUTE; // mouse movement
C>    input.mi.dx = pt.x * (ABSOLUTE_XY_MAX / screenX); input.mi.dy = pt.y * (ABSOLUTE_XY_MAX / screenY);

If MOUSEEVENTF_ABSOLUTE value is specified, dx and dy contain normalized absolute coordinates between 0 and 65,535. The event procedure maps these coordinates onto the display surface. Coordinate (0,0) maps onto the upper-left corner of the display surface; coordinate (65535,65535) maps onto the lower-right corner. In a multimonitor system, the coordinates map to the primary monitor.

Чего та вычисления неясные?

.…
C>    ZeroMemory(&input,sizeof(INPUT)); //clear out input
C>    input.type = INPUT_MOUSE;
C>    input.mi.dwFlags = MOUSEEVENTF_LEFTUP; // mouse button up
C>    SendInput(1,&input,sizeof(INPUT));
C>}
C>

C>Не судьба, видимо, с IE подружиться.

    const int nSizeX = rcClip.right - rcClip.left;
    const int nSizeY = rcClip.bottom - rcClip.top;
    // Calculate the click coordinates for the target window.
    pt.x = Round(((double) relative_point->x / m_wGaugeWidth) * nSizeX) + rcClip.left;
    pt.y = Round(((double) relative_point->y / m_wGaugeHeight) * nSizeY) + rcClip.top;

C>.…
C>>    ZeroMemory(&input,sizeof(INPUT)); //clear out input
C>>    input.type = INPUT_MOUSE;
C>>    input.mi.dwFlags = MOUSEEVENTF_LEFTUP; // mouse button up
C>>    SendInput(1,&input,sizeof(INPUT));
C>>}
C>>

C>>Не судьба, видимо, с IE подружиться.