توضیحات دوستان خوب بود. منم یه مثال می زنم...
using System;
using System.Drawing;
using System.Windows.Forms;
using System.Drawing.Drawing2D;
namespace Circle
{
public partial class CircleForm : Form
{
public CircleForm()
{
InitializeComponent();
FormBorderStyle = FormBorderStyle.None;
TransparencyKey = Color.Khaki;
}
private void CircleForm_Paint(object sender, PaintEventArgs e)
{
Rectangle rect = ClientRectangle;
e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
e.Graphics.Clear(TransparencyKey);
e.Graphics.FillEllipse(new SolidBrush(Color.LightBlue), rect);
rect.Inflate(-1, -1);
e.Graphics.DrawEllipse(new Pen(Color.DimGray), rect);
}
}
}