Rounded edges in button C# (WinForms)

This is a quick one, you may want to fine tune things and optimize quite a few details..

class RoundedButton : Button
{
   GraphicsPath GetRoundPath(RectangleF Rect, int radius)
   {
      float r2 = radius / 2f;
      GraphicsPath GraphPath = new GraphicsPath();
      GraphPath.AddArc(Rect.X, Rect.Y, radius, radius, 180, 90);
      GraphPath.AddLine(Rect.X + r2, Rect.Y, Rect.Width - r2, Rect.Y);
      GraphPath.AddArc(Rect.X + Rect.Width - radius, Rect.Y, radius, radius, 270, 90);
      GraphPath.AddLine(Rect.Width, Rect.Y + r2, Rect.Width, Rect.Height - r2);
      GraphPath.AddArc(Rect.X + Rect.Width - radius, 
                       Rect.Y + Rect.Height - radius, radius, radius, 0, 90);
      GraphPath.AddLine(Rect.Width - r2, Rect.Height, Rect.X + r2, Rect.Height);
      GraphPath.AddArc(Rect.X, Rect.Y + Rect.Height - radius, radius, radius, 90, 90);
      GraphPath.AddLine(Rect.X, Rect.Height - r2, Rect.X, Rect.Y + r2);
      GraphPath.CloseFigure();
      return GraphPath;
   }

   protected override void OnPaint(PaintEventArgs e)
   {
      base.OnPaint(e);
      RectangleF Rect = new RectangleF(0, 0, this.Width, this.Height);
      using (GraphicsPath GraphPath = GetRoundPath(Rect, 50))
      {
        this.Region = new Region(GraphPath);
        using (Pen pen = new Pen(Color.CadetBlue, 1.75f))
        {
            pen.Alignment = PenAlignment.Inset;
            e.Graphics.DrawPath(pen, GraphPath);
        }
      }
   }
}

Obviously, since we have a class we can cache the GraphicsPath in a class variable. And of course you pick the color..

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.ComponentModel;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;


namespace button2
{
    public partial class Form1 : Form
    {
        private Button button1;
        private GroupBox box;
        public Form1()
        {
            InitializeComponent();
            show();
        }
        private void show()
        {
            box = new GroupBox();
            button1 = new Button();
            button1.Location = new Point(50, 50);
            ElipseControl nn = new ElipseControl();            
            nn.TargetControl = button1;            
            button1.Text = "First Name";
            button1.BackColor = Color.Cyan;
            button1.FlatStyle = FlatStyle.Flat;
            button1.FlatAppearance.BorderSize = 0;
            button1.FlatAppearance.BorderColor = Color.White;
            nn.CornerRadius = 10;

            button1.ForeColor = Color.Blue;
            button1.Font = new Font("Arial", 9, FontStyle.Bold);
            box.Controls.Add(button1);
            box.AutoSize = true;


            this.Controls.Add(box);

        }
    }
    class ElipseControl : Component
    {
        [DllImport("Gdi32.dll", EntryPoint = "CreateRoundRectRgn")]
        public static extern IntPtr CreateRoundRectRgn
            (
               int nLeftRect,
               int nTopRect,
               int nRightRect,
               int nBottomRect,
               int nWidthEllipse,
               int nHeightEllipse
            );
        private Control _cntrl;
        private int _CornerRadius = 30;

        public Control TargetControl
        {
            get { return _cntrl; }
            set
            {
                _cntrl = value;
                _cntrl.SizeChanged += (sender, eventArgs) => _cntrl.Region = Region.FromHrgn(CreateRoundRectRgn(0, 0, _cntrl.Width, _cntrl.Height, _CornerRadius, _CornerRadius));
            }
        }

        public int CornerRadius
        {
            get { return _CornerRadius; }
            set
            {
                _CornerRadius = value;
                if (_cntrl != null)
                    _cntrl.Region = Region.FromHrgn(CreateRoundRectRgn(0, 0, _cntrl.Width, _cntrl.Height, _CornerRadius, _CornerRadius));
            }
        }
    }
}

This is a tweak on TaW's answer to more easily tweak the borderRadius and borderThickness. If you get random white space between the border and the button background color, m needs to be tweaked.

public class RoundedButton : Button
{
  GraphicsPath GetRoundPath(RectangleF Rect, int radius)
  {
    float m = 2.75F;
    float r2 = radius / 2f;
    GraphicsPath GraphPath = new GraphicsPath();

    GraphPath.AddArc(Rect.X + m, Rect.Y + m, radius, radius, 180, 90);
    GraphPath.AddLine(Rect.X + r2 + m, Rect.Y + m, Rect.Width - r2 - m, Rect.Y + m);
    GraphPath.AddArc(Rect.X + Rect.Width - radius - m, Rect.Y + m, radius, radius, 270, 90);
    GraphPath.AddLine(Rect.Width - m, Rect.Y + r2, Rect.Width - m, Rect.Height - r2 - m);
    GraphPath.AddArc(Rect.X + Rect.Width - radius - m,
                   Rect.Y + Rect.Height - radius - m, radius, radius, 0, 90);
    GraphPath.AddLine(Rect.Width - r2 - m, Rect.Height - m, Rect.X + r2 - m, Rect.Height - m);
    GraphPath.AddArc(Rect.X + m, Rect.Y + Rect.Height - radius - m, radius, radius, 90, 90);
    GraphPath.AddLine(Rect.X + m, Rect.Height - r2 - m, Rect.X + m, Rect.Y + r2 + m);

    GraphPath.CloseFigure();
    return GraphPath;
  }

  protected override void OnPaint(PaintEventArgs e)
  {
    int borderRadius = 50;
    float borderThickness = 1.75f;
    base.OnPaint(e);
    RectangleF Rect = new RectangleF(0, 0, this.Width, this.Height);
    GraphicsPath GraphPath = GetRoundPath(Rect, borderRadius);

    this.Region = new Region(GraphPath);
    using (Pen pen = new Pen(Color.Silver, borderThickness))
    {
      pen.Alignment = PenAlignment.Inset;
      e.Graphics.DrawPath(pen, GraphPath);
    }
  }
}

Cheers!