I've recently added this to Coedit: the split between the widgets can be srolled and the mouse pointer follows.

Then As I'm building a GUI framework in D I've added what's necessary to reproduce it in D. It's fun with free mouse wheels.

https://vimeo.com/170517792

And it's stupid simple:

struct Mouse
{
    private OsWindowHandle _winHdl;

    /// Constructs an instance with the handle of the target window.
    this(OsWindowHandle winHdl)
    {
        _winHdl = winHdl;
    }

    /// Returns the mouse position as a point of int.
    Point!int position() const
    {
        Point!int result;
        version(linux)
        {
            int a,b;
            uint c;
            Window r,t;
            XQueryPointer(display, _winHdl, &r, &t, &a, &b,
                &result.x, &result.y, &c);
            return result;
        }
    }

    /// Sets the mouse position from a point.
    void position(T)(Point!T value) const
    if (isNumeric!T)
    {
        version(linux)
        {
            XWarpPointer(display, _winHdl, _winHdl, 0, 0, 0, 0,
                cast(int) value.x, cast(int) value.y);
        }
        else static assert(0);
    }
}