用Reactive Extensions快速实现鼠标手势功能

鼠标手势非常方便，在很多程序中得到了广泛应用。在这里我要介绍一种通过用Reactive Extensions快速实现鼠标手势功能的方法，以供有需要的朋友参考。

一般用的那些只有上下左右的鼠标手势的识别原理并不复杂，只需要对鼠标轨迹进行定点采集，根据偏移的角度进行降噪处理，折换成上下左右四个方向即可。具体代码可以参考下文中的GetDirection方法（这个函数不是我写的，以前在网上找的，原始出处不记得了）。通过用Reactive extensions可以非常容易的实现这一过程。具体代码如下： 

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        Process();
    }

    private void Process()
    {
        var mouseDown = Observable.FromEventPattern<MouseEventArgs>(this, "MouseDown");
        var mouseMove = Observable.FromEventPattern<MouseEventArgs>(this, "MouseMove");
        var mouseUp = Observable.FromEventPattern<MouseEventArgs>(this, "MouseUp");

        var mousePath = mouseMove.SkipUntil(mouseDown).TakeUntil(mouseUp).Select(i => i.EventArgs.Location);

        mousePath.Take(1).Subscribe(_ => { }, () => label1.Text = "waitting for mouse up...");
        ProcessMouseGesture(mousePath);
    }


    void ProcessMouseGesture(IObservable<Point> mousePath)
    {
        //这里只是取0.1秒间隔作为采集点，不是很合适，还要把距离拿来一起算可能更精确一些
        var points = mousePath.Sample(TimeSpan.FromSeconds(0.1));

        var directions = (from direction in points.Zip(points.Skip(1), (p1, p2) => GetDirection(p1, p2))
                            where direction != MouseGestureDirection.Unknown
                            select direction).DistinctUntilChanged();

        var directionList = new List<MouseGestureDirection>();
        directions.Subscribe(d => directionList.Add(d), () =>
            {
                label1.Text = string.Join(",", directionList.ToArray());
                Process();
            });
    }

    static MouseGestureDirection GetDirection(Point start, Point end)
    {
        const double maxAngleError = 30;

        int deltaX = end.X - start.X;
        int deltaY = end.Y - start.Y;

        double length = Math.Sqrt(deltaX * deltaX + deltaY * deltaY);

        double sin = deltaX / length;
        double cos = deltaY / length;

        double angle = Math.Asin(Math.Abs(sin)) * 180 / Math.PI;

        if ((sin >= 0) && (cos < 0))
            angle = 180 - angle;
        else if ((sin < 0) && (cos < 0))
            angle = angle + 180;
        else if ((sin < 0) && (cos >= 0))
            angle = 360 - angle;

        //direction recognition
        if ((angle > 360 - maxAngleError) || (angle < 0 + maxAngleError))
            return MouseGestureDirection.Down;
        else if ((angle > 90 - maxAngleError) && (angle < 90 + maxAngleError))
            return MouseGestureDirection.Right;
        else if ((angle > 180 - maxAngleError) && (angle < 180 + maxAngleError))
            return MouseGestureDirection.Up;
        else if ((angle > 270 - maxAngleError) && (angle < 270 + maxAngleError))
            return MouseGestureDirection.Left;
        else return MouseGestureDirection.Unknown;
    }
}


enum MouseGestureDirection
{
    Unknown,
    Up,
    Right,
    Down,
    Left
}

由于我对Reactive Extensions不熟，只是偶尔有空的时候看了看，目前还属于管中窥豹阶段，上述代码并非最佳实践，本文这里只是给出了一种思路和方法，如果谁有更合适的实现，欢迎留言指正。