WPF - Two Finger Horizontal scrolling on Macbook pro trackpad

Question

The OS is Windows 8 on a Retina Macbook PRO.

i need to support both vertical scrolling using the trackpad and horizontal scrolling in my app.

I would like to move the WPF scrollviewer position based on the two finger swipes up-down (vertical scrolling) and left-right (horizontal scrolling).

As far as i see the vertical scrolling on the trackpad gets translated to a mouse wheel event in the framework. However, I found no way to recognize if a mouse wheel event is a horizontal scroll.

what events should i handle in WPF to be able to implement this?

Answer 1

I wrote an article especially for you to know how to handle horizontal scrolling of touchpad in a WPF application. That is Support Horizontal Scrolling of TouchPad in WPF Application - walterlv

---

We need to fetch WM_MOUSEHWHEEL message from our WPF window. Yes! That mouse wheel message. We fetch vertical data from it before, but we now fetch horizontal data from it.

At first, we should hook the window message.

protected override void OnSourceInitialized(EventArgs e)
{
    var source = PresentationSource.FromVisual(_board);
    ((HwndSource) source)?.AddHook(Hook);
}

private IntPtr Hook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
{
    // Handle window message here.
    return IntPtr.Zero;
}

Next, handle WM_MOUSEHWHEEL:

const int WM_MOUSEHWHEEL = 0x020E;

private IntPtr Hook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
{
    switch (msg)
    {
        case WM_MOUSEHWHEEL:
            int tilt = (short) HIWORD(wParam);
            OnMouseTilt(tilt);
            return (IntPtr) 1;
    }
    return IntPtr.Zero;
}

/// <summary>
/// Gets high bits values of the pointer.
/// </summary>
private static int HIWORD(IntPtr ptr)
{
    var val32 = ptr.ToInt32();
    return ((val32 >> 16) & 0xFFFF);
}

/// <summary>
/// Gets low bits values of the pointer.
/// </summary>
private static int LOWORD(IntPtr ptr)
{
    var val32 = ptr.ToInt32();
    return (val32 & 0xFFFF);
}

private void OnMouseTilt(int tilt)
{
    // Write your horizontal handling codes here.
}

You can write horizontal scrolling code in OnMouseTilt method.

Better yet, you could pack all the codes above in a more common class and raise a MouseTilt event just like raising MouseWheel event.

Answer 2

Completing the answer walterlv

private void OnMouseTilt(int tilt)
{
    UIElement element = Mouse.DirectlyOver as UIElement;

    if (element == null) return;

    ScrollViewer scrollViewer = element is ScrollViewer viewer ? viewer : FindParent<ScrollViewer>(element);

    if (scrollViewer == null)
        return;

    scrollViewer.ScrollToHorizontalOffset(scrollViewer.HorizontalOffset + tilt);
}

public static T FindParent<T>(DependencyObject child) where T : DependencyObject
{
    DependencyObject parentObject = VisualTreeHelper.GetParent(child);

    if (parentObject == null) return null;

    T parent = parentObject as T;
    if (parent != null)
        return parent;
    else
        return FindParent<T>(parentObject);
}

Answer 3

Improve walterlv's answer and fix arithmetic overflow on 64 bit system when scrolling left:

/// <summary>
/// Gets high bits values of the pointer.
/// </summary>
private static int HIWORD(IntPtr ptr)
{
    unchecked
    {
        if (Environment.Is64BitOperatingSystem)
        {
            var val64 = ptr.ToInt64();
            return (short) ((val64 >> 16) & 0xFFFF);
        }
        var val32 = ptr.ToInt32();
        return (short) ((val32 >> 16) & 0xFFFF);   
    }
}

/// <summary>
/// Gets low bits values of the pointer.
/// </summary>
private static int LOWORD(IntPtr ptr)
{
    unchecked
    {
        if (Environment.Is64BitOperatingSystem)
        {
            var val64 = ptr.ToInt64();
            return (short)(val64 & 0xFFFF);
        }

        var val32 = ptr.ToInt32();
        return (short)(val32 & 0xFFFF);
    }
}