GradientButton.cs

_background = new NControlView
 {
    DrawingFunction = (canvas, rect) =>
    {
         var brush = new LinearGradientBrush(
          Point.Zero,
          Point.OneX,
          Color.FromHex("#6C6FEC").ToNColor(),
          Color.FromHex("#5A41B9").ToNColor());

          var curveSize = BorderRadius;
          var width = rect.Width;
          var height = rect.Height;

          canvas.DrawPath(new PathOp[]{
                 new MoveTo(curveSize, 0),
                 // Top Right corner
                 new LineTo(width-curveSize, 0),
                 new CurveTo(
                    new Point(width-curveSize, 0),
                    new Point(width, 0),
                    new Point(width, curveSize)
                 ),
                 new LineTo(width, height-curveSize),
                 // Bottom right corner
                 new CurveTo(
                    new Point(width, height-curveSize),
                    new Point(width, height),
                    new Point(width-curveSize, height)
                 ),
                 new LineTo(curveSize, height),
                 // Bottom left corner
                 new CurveTo(
                   new Point(curveSize, height),
                   new Point(0, height),
                   new Point(0, height-curveSize)
                 ),
                 new LineTo(0, curveSize),
                 new CurveTo(
                    new Point(0, curveSize),
                    new Point(0, 0),
                    new Point(curveSize, 0)
                ),
                new ClosePath()
            }, null, brush);
         }
};