optimizer/Optimizer/Controls/MoonButton.cs

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;

namespace Optimizer
{
    public sealed class MoonButton : Button
    {
        private int _borderRadius = 5;

        public MoonButton()
        {
            BackColor = Color.White;
            ForeColor = Color.Black;
            FlatStyle = FlatStyle.Flat;
            FlatAppearance.BorderSize = 0;
        }

        private GraphicsPath GetFigurePath(Rectangle rect, int radius)
        {
            GraphicsPath path = new GraphicsPath();
            float curveSize = radius * 2F;

            path.StartFigure();
            path.AddArc(rect.X, rect.Y, curveSize, curveSize, 180, 90);
            path.AddArc(rect.Right - curveSize, rect.Y, curveSize, curveSize, 270, 90);
            path.AddArc(rect.Right - curveSize, rect.Bottom - curveSize, curveSize, curveSize, 0, 90);
            path.AddArc(rect.X, rect.Bottom - curveSize, curveSize, curveSize, 90, 90);
            path.CloseFigure();

            return path;
        }

        protected override void OnPaint(PaintEventArgs pevent)
        {
            base.OnPaint(pevent);

            pevent.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
            pevent.Graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
            pevent.Graphics.InterpolationMode = InterpolationMode.High;

            Rectangle rectSurface = ClientRectangle;
            Rectangle rectBorder = Rectangle.Inflate(rectSurface, 0, 0);

            using (GraphicsPath pathSurface = GetFigurePath(rectSurface, _borderRadius))
            using (GraphicsPath pathBorder = GetFigurePath(rectBorder, _borderRadius))
            using (Pen penSurface = new Pen(Parent.BackColor, 2))
            {
                Region = new Region(pathSurface);
                pevent.Graphics.DrawPath(penSurface, pathSurface);
            }
        }

        protected override void OnResize(EventArgs e)
        {
            base.OnResize(e);

            if (_borderRadius > Height)
                _borderRadius = Height;
        }
    }
}