.NET (Core and Framework)

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

	Graphics g=e.Graphics;
	g.SmoothingMode=SmoothingMode.AntiAlias;//<------------------ Cause no effect!

	GraphicsPath gp=new GraphicsPath();

	int border=5;

	int x=0;
	int y=0;
	int w=this.Width;
	int h=this.Height;
	int r=10;
	int d=r*2;

	Point lp1= new Point(x+r,y);
	Point lp2= new Point(x+w-r,y);
	Point lp3= new Point(x+w,y+r);
	Point lp4= new Point(x+w,y+h-r);
	Point lp5= new Point(x+w-r,y+h);
	Point lp6= new Point(x+r,y+h);
	Point lp7= new Point(x,y+h-r);
	Point lp8= new Point(x,y+r);

	Rectangle ar1= new Rectangle(x,y,d,d);
	Rectangle ar2= new Rectangle(x+w-d,y,d,d);
	Rectangle ar3= new Rectangle(x+w-d,y+h-d,d,d);
	Rectangle ar4= new Rectangle(x,y+h-d,d,d);

	Pen p=new Pen(Brushes.Black,border);
	//p.DashStyle=DashStyle.Solid; <----------------------------- Is it needed?
	SolidBrush b=new SolidBrush(System.Drawing.Color.Wheat);
	
	gp.AddArc(ar1,180,90);
	gp.AddLine(lp1,lp2);
	gp.AddArc(ar2,270,90);
	gp.AddLine(lp3,lp4);
	gp.AddArc(ar3,0,90);
	gp.AddLine(lp5,lp6);
	gp.AddArc(ar4,90,90);
	gp.AddLine(lp7,lp8);

	g.DrawPath(p,gp);
	//g.FillPath(b,gp);//<---------------------- Is it needed?
	this.Region=new Region(gp);

	x=0;
	y=0;
	w=this.Width;
	h=this.Height;

	lp1= new Point(x+r,y);
	lp2= new Point(x+w-r,y);
	lp3= new Point(x+w,y+r);
	lp4= new Point(x+w,y+h-r);
	lp5= new Point(x+w-r,y+h);
	lp6= new Point(x+r,y+h);
	lp7= new Point(x,y+h-r);
	lp8= new Point(x,y+r);

	ar1= new Rectangle(x,y,d,d);
	ar2= new Rectangle(x+w-d,y,d,d);
	ar3= new Rectangle(x+w-d,y+h-d,d,d);
	ar4= new Rectangle(x,y+h-d,d,d);

	g.DrawArc(p,ar1,180,90);
	g.DrawLine(p,lp1,lp2);
	g.DrawArc(p,ar2,270,90);
	g.DrawLine(p,lp3,lp4);
	g.DrawArc(p,ar3,0,90);
	g.DrawLine(p,lp5,lp6);
	g.DrawArc(p,ar4,90,90);
	g.DrawLine(p,lp7,lp8);

	this.BackColor=Color.Wheat;

	g.Dispose();
}