Public Class Form1

　Private pic As PictureBox

　Private center As New Point(10, 10)

　Private r As Integer = 10

　Private Sub Form1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown

　Select Case e.KeyCode

　Case Keys.Up

　If center.Y > r Then center.Y -= 1 Else Return

　Case Keys.Down

　If center.Y < pic.Height - r Then center.Y += 1 Else Return

　Case Keys.Left

　If center.X > r Then center.X -= 1 Else Return

　Case Keys.Right

　If center.X < pic.Width - r Then center.X += 1 Else Return

　Case Else

　Return

　End Select

　pic.Refresh()

　End Sub

　Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

　pic = New PictureBox With {.Dock = DockStyle.Fill, .BorderStyle = BorderStyle.FixedSingle}

　AddHandler pic.Paint, AddressOf pic_Paint

　Me.Controls.Add(pic)

　End Sub

　Private Sub pic_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs)

　e.Graphics.Clear(Color.Black)

　e.Graphics.SmoothingMode = Drawing2D.SmoothingMode.HighQuality

　e.Graphics.DrawEllipse(Pens.Red, New Rectangle(center.X - r, center.Y - r, r * 2, r * 2))

　End Sub

　End Class

　C# code

　using System;

　using System.Collections.Generic;

　using System.ComponentModel;

　using System.Data;

　using System.Drawing;

　using System.Linq;

　using System.Text;

　using System.Windows.Forms;

　namespace WindowsFormsApplication1

　{

　public partial class Form1 : Form

　{

　private PictureBox pic;

　private Point center = new Point(10, 10);

　private int r = 10;

　public Form1()

　{

　InitializeComponent();

　}

　private void Form1_Load(object sender, EventArgs e)

　{

　pic = new PictureBox { Dock = DockStyle.Fill, BorderStyle = BorderStyle.FixedSingle };

　pic.Paint += pic_Paint;

　this.Controls.Add(pic);

　}

　private void Form1_KeyDown(object sender, KeyEventArgs e)

　{

　switch (e.KeyCode)

　{

　case Keys.Up:

　if (center.Y > r) center.Y -= 1; else return;

　break;

　case Keys.Down:

　if (center.Y < pic.Height - r) center.Y += 1; else return;

　break;

　case Keys.Left:

　if (center.X > r) center.X -= 1; else return;

　break;

　case Keys.Right:

　if (center.X < pic.Width - r) center.X += 1; else return;

　break;

　default:

　return;

　}

　pic.Refresh();

　}

　private void pic_Paint(object sender, System.Windows.Forms.PaintEventArgs e)

　{

　e.Graphics.Clear(Color.Black);

　e.Graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

　e.Graphics.DrawEllipse(Pens.Red, new Rectangle(center.X - r, center.Y - r, r * 2, r * 2));

　}

　}

　}