public enum TriangularButtonDirection
{
    Up = 0,
    Down = 1
}

class TriangularButton : Button
{
    public TriangularButton(IntPtr javaReference, JniHandleOwnership transfer) : base(javaReference, transfer)
    {
        this.Initialize(null);
    }

    public TriangularButton(Context context) : base(context)
    {
        this.Initialize(null);
    }

    public TriangularButton(Context context, IAttributeSet attrs) : base(context, attrs)
    {
        this.Initialize(attrs);
    }

    public TriangularButton(Context context, IAttributeSet attrs, int defStyleAttr) : base(context, attrs, defStyleAttr)
    {
        this.Initialize(attrs);
    }

    public TriangularButton(Context context, IAttributeSet attrs, int defStyleAttr, int defStyleRes) : base(context, attrs, defStyleAttr, defStyleRes)
    {
        this.Initialize(attrs);
    }

    private TriangularButtonDirection _direction = TriangularButtonDirection.Down;

    private void Initialize(IAttributeSet attributeSet)
    {
        if (attributeSet != null)
        {
            TypedArray a = this.Context.ObtainStyledAttributes(attributeSet, Resource.Styleable.TriangularButton);

            int direction = a.GetInt(Resource.Styleable.TriangularButton_direction, -1);
            if (direction > -1)
                this._direction = (TriangularButtonDirection)direction;
            a.Recycle();
        }
    }

    public override bool OnTouchEvent(MotionEvent e)
    {
        float x = e.GetX();
        float y = e.GetY();
        int width = this.MeasuredWidth;
        PointF point1Draw;
        PointF point2Draw;
        PointF point3Draw;
        if (this._direction == TriangularButtonDirection.Up)
        {
            point1Draw = new PointF(0, 3f * width / 4);
            point2Draw = new PointF(width, 3f * width / 4);
            point3Draw = new PointF(width / 2f, 0);
        }
        else
        {
            point1Draw = new PointF(0, 0);
            point2Draw = new PointF(width, 0);
            point3Draw = new PointF(width / 2f, 3f * width / 4);
        }
        bool test = PointInTriangle(new PointF(x, y), point1Draw, point2Draw, point3Draw);
        if (test)
            base.OnTouchEvent(e);
        return (test);
    }

    public static bool PointInTriangle(PointF p, PointF p0, PointF p1, PointF p2)
    {
        float s = p0.Y * p2.X - p0.X * p2.Y + (p2.Y - p0.Y) * p.X + (p0.X - p2.X) * p.Y;
        float t = p0.X * p1.Y - p0.Y * p1.X + (p0.Y - p1.Y) * p.X + (p1.X - p0.X) * p.Y;
        if ((s < 0) != (t < 0))
            return false;
        float a = -p1.Y * p2.X + p0.Y * (p2.X - p1.X) + p0.X * (p1.Y - p2.Y) + p1.X * p2.Y;
        if (a < 0.0)
        {
            s = -s;
            t = -t;
            a = -a;
        }
        return s > 0 && t > 0 && (s + t) <= a;
    }

    protected override void OnMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {
        base.OnMeasure(widthMeasureSpec, heightMeasureSpec);
        this.SetMeasuredDimension(this.MeasuredWidth, 3 * this.MeasuredWidth / 4);
    }

    public override void Draw(Canvas canvas)
    {
        int width = this.MeasuredWidth;

        Paint paintFill = new Paint(PaintFlags.AntiAlias);
        paintFill.StrokeWidth = 2;
        paintFill.Color = this.Hovered ? Color.Red : new Color(242, 180, 54);
        paintFill.SetStyle(Android.Graphics.Paint.Style.Fill);
        paintFill.AntiAlias = true;

        Paint paintStroke = new Paint(PaintFlags.AntiAlias);
        paintStroke.StrokeWidth = 2;
        paintStroke.Color = Color.White;
        paintStroke.SetStyle(Android.Graphics.Paint.Style.Stroke);
        paintStroke.AntiAlias = true;

        PointF point1Draw;
        PointF point2Draw;
        PointF point3Draw;
        if (this._direction == TriangularButtonDirection.Up)
        {
            point1Draw = new PointF(0, 3f * width / 4);
            point2Draw = new PointF(width, 3f * width / 4);
            point3Draw = new PointF(width / 2f, 0);
        }
        else
        {
            point1Draw = new PointF(0, 0);
            point2Draw = new PointF(width, 0);
            point3Draw = new PointF(width / 2f, 3f * width / 4);
        }

        Path path = new Path();
        path.SetFillType(Path.FillType.EvenOdd);
        path.MoveTo(point1Draw.X, point1Draw.Y);
        path.LineTo(point2Draw.X, point2Draw.Y);
        path.LineTo(point3Draw.X, point3Draw.Y);
        path.LineTo(point1Draw.X, point1Draw.Y);
        path.Close();

        canvas.DrawPath(path, paintFill);
        canvas.DrawPath(path, paintStroke);
    }
}