画面に大量にテキストを描画すると遅くなることは防げますか？

using System;
using System.Drawing;
using System.ComponentModel;
using System.Windows.Forms;
using System.Runtime.InteropServices;

public class Form1 : Form {
	private Container components = null;
	MyCaret caret;
	string[] lines;
	Point cur;
	Point org;
	bool bSel;

	public Form1() {
		InitializeComponent();

		caret = new MyCaret(this);
		lines = new string[] {
								 "public class MyApp {",
								 "    System.Console.WriteLine(\"Hello,World\");",
								 "}"};
		cur = Point.Empty;
		org = Point.Empty;
		bSel = false;
	}

	protected override void Dispose( bool disposing ) {
		if( disposing ) {
			if (components != null) {
				components.Dispose();
			}
		}
		base.Dispose( disposing );
	}

	protected override void OnPaint(PaintEventArgs e) {
		base.OnPaint (e);
		StringFormat fmt = StringFormat.GenericTypographic;
		fmt.FormatFlags |= StringFormatFlags.MeasureTrailingSpaces;
		for (int i = 0; i < lines.Length; ++i)
			e.Graphics.DrawString(lines[i], Font, new SolidBrush(this.ForeColor), 
				0, Font.Height * i, StringFormat.GenericTypographic);
		if (bSel) {
			DrawSelected(e.Graphics);
		}
	}

	protected override void OnKeyDown(KeyEventArgs e) {
		if (e.Shift) {
			if (!bSel) {
				org = cur;
				bSel = true;
			}
		}
		else {
			org = cur;
			bSel = false;
		}

		switch (e.KeyCode) {
			case Keys.Left:
				if (cur.X > 0) 
					--cur.X;
				else if (cur.Y > 0) {
					--cur.Y;
					cur.X = lines[cur.Y].Length;
				}
				break;
			case Keys.Right:
				if (cur.X < lines[cur.Y].Length)
					++cur.X;
				else if (cur.Y < lines.Length - 1) {
					++cur.Y;
					cur.X = 0;
				}
				break;
			case Keys.Up:
				if (cur.Y > 0) {
					--cur.Y;
					if (cur.X > lines[cur.Y].Length)
						cur.X = lines[cur.Y].Length;
				}
				break;
			case Keys.Down:
				if (cur.Y < lines.Length - 1) {
					++cur.Y;
					if (cur.X > lines[cur.Y].Length)
						cur.X = lines[cur.Y].Length;
				}
				break;
		}
		MoveCaret();
		Invalidate();
	}

	void DrawSelected(Graphics g) {
		Point bgn;
		Point end;

		if (org.Y < cur.Y || org.Y == cur.Y && org.X < cur.X) {
			bgn = org;
			end = cur;
		}
		else {
			bgn = cur;
			end = org;
		}

		int p;
		int q;
		PointF lt = PointF.Empty;
		PointF rb = PointF.Empty;
		for (int i = bgn.Y; i <= end.Y; ++i) {
			lt.Y = i * Font.Height;
			rb.Y = (i + 1) * Font.Height;

			if (i == bgn.Y) { 
				lt.X = CalcWidth(g, lines[i].Substring(0, bgn.X));
				p = bgn.X;
			}
			else { 
				lt.X = 0; 
				p = 0;
			}
			if (i == end.Y) {
				rb.X = CalcWidth(g, lines[i].Substring(0, end.X));
				q = end.X;
			}
			else {
				rb.X = CalcWidth(g, lines[i]);
				q = lines[i].Length;
			}
			g.FillRectangle(Brushes.DarkBlue, lt.X, lt.Y, rb.X - lt.X, rb.Y - lt.Y);
			g.DrawString(lines[i].Substring(p, q - p), Font, new SolidBrush(Color.White), 
				lt.X, lt.Y, StringFormat.GenericTypographic);
		}
	}

	float CalcWidth(Graphics g, string s) {
		StringFormat fmt = StringFormat.GenericTypographic;
		fmt.FormatFlags |= StringFormatFlags.MeasureTrailingSpaces;
		SizeF size = g.MeasureString(s, Font, Point.Empty, fmt);
		return size.Width;
	}

	void MoveCaret() {
		using (Graphics g = Graphics.FromHwnd(Handle)) {
			float w = CalcWidth(g, lines[cur.Y].Substring(0, cur.X));
			caret.Position = new Point((int)w, Font.Height * cur.Y);
		}
	}

	private void InitializeComponent() {
		this.AutoScaleBaseSize = new System.Drawing.Size(6, 12);
		this.ClientSize = new System.Drawing.Size(292, 266);
		this.Font = new System.Drawing.Font("ＭＳ ゴシック", 9F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0)));
		this.Name = "Form1";
		this.Text = "Form1";

	}

	[STAThread]
	static void Main() {
		Application.Run(new Form1());
	}
}

public class MyCaret {
	[DllImport("user32.dll")]
	public static extern int CreateCaret(IntPtr hwnd, IntPtr hbm, int cx, int cy);
	[DllImport("user32.dll")]
	public static extern int DestroyCaret();
	[DllImport("user32.dll")]
	public static extern int SetCaretPos(int x, int y);
	[DllImport("user32.dll")]
	public static extern int ShowCaret(IntPtr hwnd);
	[DllImport("user32.dll")]
	public static extern int HideCaret(IntPtr hwnd);

	Control ctrl;
	Size	size;
	Point	pos;
	bool	bVisible;

	public MyCaret(Control ctrl) {
		this.ctrl = ctrl;
		Position = Point.Empty;
		Size = new Size(1, ctrl.Font.Height);
		Control.GotFocus += new EventHandler(OnGotFocus);
		Control.LostFocus += new EventHandler(OnLostFocus);

		if (ctrl.Focused)
			OnGotFocus(ctrl, new EventArgs());
	}

	public Control Control {
		get { return ctrl; }
	}

	public Size Size {
		get { return size; }
		set { size = value; }
	}

	public Point Position {
		get { 
			return pos; 
		}
		set { 
			pos = value; 
			SetCaretPos(pos.X, pos.Y);
		}
	}

	public bool Visible {
		get {
			return bVisible;
		}
		set {
			bVisible = value;
			if (bVisible)
				ShowCaret(Control.Handle);
			else
				HideCaret(Control.Handle);
		}
	}

	public void Dispose() {
		if (ctrl.Focused)
			OnLostFocus(ctrl, new EventArgs());
		Control.GotFocus -= new EventHandler(OnGotFocus);
		Control.LostFocus -= new EventHandler(OnLostFocus);
	}

	private void OnGotFocus(object sender, EventArgs e) {
		CreateCaret(Control.Handle, IntPtr.Zero, Size.Width, Size.Height);
		SetCaretPos(Position.X, Position.Y);
		Visible = true;
	}

	private void OnLostFocus(object sender, EventArgs e) {
		Visible = false;
		DestroyCaret();
	}
}