namespace TestApp
{
    public partial class TestForm
    {
        private BufferedGraphics graphicsBuffer;
        private BufferedGraphicsContext bufferContext = BufferedGraphicsManager.Current;

        public TestForm()
        {
            InitializeComponent();
            UpdateGraphicsBuffer();
        }

        private void UpdateGraphicsBuffer()
        {
            bufferContext.MaximumBuffer = new Size(panelRender.Width + 1, panelRender.Height + 1);
            graphicsBuffer = bufferContext.Allocate(Graphics.FromHwnd(panelRender.Handle), new Rectangle(49, 49, 100, 100));
            graphicsBuffer.Graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        }

        private void TestForm_Load(object sender, EventArgs e)
        {
            graphicsBuffer.Graphics.DrawRectangle(new Pen(Color.Red), 50, 50, 50, 50);
        }
    }
}

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

namespace DoubleBufferTest
{
    public partial class Form1 : Form
    {
        private BufferedGraphics graphicsBuffer = null;
        private BufferedGraphicsContext bufferContext = BufferedGraphicsManager.Current;

        public Form1()
        {
            this.SetStyle(ControlStyles.SupportsTransparentBackColor | ControlStyles.UserPaint, true);
            this.UpdateStyles();
            InitializeComponent();
            UpdateGraphicsBuffer();
        }

        private void UpdateGraphicsBuffer()
        {
            bufferContext.MaximumBuffer = new Size(panel1.Width + 1, panel1.Height + 1);
            graphicsBuffer = bufferContext.Allocate(Graphics.FromHwnd(panel1.Handle), new Rectangle(10, 10, 50, 50));
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            graphicsBuffer.Graphics.DrawRectangle(new Pen(Color.Red, 3.0f), 20, 20, 10, 10);
            graphicsBuffer.Render();
        }
    }
}