Problem with Syntax Highlighting in RichTextBox

Hiiii.

I have a problem with Syntax Highlighting in a RichTextBox. I'm using the following code, found in a thread here.

Code:

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        [DllImport("user32.dll")]
        extern static int SendMessage(int hwnd, int message, int wparam, int lparam);
        [DllImport("user32.dll")]
        extern static int LockWindowUpdate(int hwnd);

        int[] strComm = null;

        KeyWords[] Words = new KeyWords[14];

        public enum EditMessages
        {
            LineIndex = 187,
            LineFromChar = 201,
            GetFirstVisibleLine = 206,
            CharFromPos = 215,
            PosFromChar = 1062
        }

        public struct KeyWords
        {
            public string Word;
            public Color Color;
        }

        public Form1()
        {
            InitializeComponent();

        }

        private void rtfText_TextChanged(object sender, EventArgs e)
        {
            //Handles rtfText.KeyPress
            ColorVisibleLines(rtfText);
        }

        public void ColorVisibleLines(RichTextBox rtfText)
        {
            int FirstLine = FirstVisibleLine();
            int LastLine = LastVisibleLine();
            int FirstVisibleChar;
            int i = FirstLine;

            if ((FirstLine == 0) & (LastLine == 0))
            {
                // If there is no text in the control, it will run an error
                // So, if there isn't any text, just exit
                return; // TODO: might not be correct. Was : Exit Sub
            }
            else
            {
                while (i < LastLine)
                {
                    FirstVisibleChar = GetCharFromLineIndex(FirstLine);
                    ColorLineNumber(rtfText, FirstLine, FirstVisibleChar);
                    FirstLine += 1;
                    i += 1;
                }
            }
        }

        public int FirstVisibleLine()
        {
            return SendMessage(rtfText.Handle.ToInt32(), (int)EditMessages.GetFirstVisibleLine, 0, 0);
        }

        public int GetCharFromLineIndex(int LineIndex)
        {
            return SendMessage(rtfText.Handle.ToInt32(), (int)EditMessages.LineIndex, LineIndex, 0);
        }

        public int LastVisibleLine()
        {
            int LastLine = FirstVisibleLine() + (rtfText.Height / rtfText.Font.Height);
            if (LastLine > rtfText.Lines.Length | LastLine == 0)
            {
                LastLine = rtfText.Lines.Length;
            }
            return LastLine;
        }

        public void ColorRtb(RichTextBox rtftext)
        {
            int FirstVisibleChar;
            int i = 0;

            while (i < rtftext.Lines.Length)
            {
                FirstVisibleChar = GetCharFromLineIndex(i);
                ColorLineNumber(rtftext, i, FirstVisibleChar);
                i += 1;
            }
        }

        public void ColorLineNumber(RichTextBox rtfText, int LineIndex, int lStart)
        {
            string Line = rtfText.Lines[LineIndex].ToLower();
            int i = 0;
            int Instance;
            int SelectionAt = rtfText.SelectionStart;

            // Lock the update
            LockWindowUpdate(rtfText.Handle.ToInt32());

            // Color the line black to remove any previous coloring
            rtfText.SelectionStart = lStart;
            rtfText.SelectionLength = Line.Length;
            rtfText.SelectionColor = Color.Black;

            // Loop through all the Keywords
            while (i < Words.Length)
            {

                // See if the word is in the Line
                //Instance = string.Compare(Line, Words[i].Word); // InStr(Line, Words[i].Word);
                Instance = Line.IndexOf(Words[i].Word) + 1;

                // If the lines contains the word, color it
                if (Instance != 0)
                {
                    rtfText.SelectionStart = (lStart + Instance - 1);
                    rtfText.SelectionLength = Words[i].Word.Length;
                    rtfText.SelectionColor = Words[i].Color;
                }

                i += 1;
            }

            // Find any comments
            Instance = Line.IndexOf("//") + 1;

            // If there are comments, color them
            if (Instance != 0)
            {
                rtfText.SelectionStart = (lStart + Instance - 1);
                rtfText.SelectionLength = (Line.Length - Instance + 1);
                rtfText.SelectionColor = Color.Green;
            }

            if (Instance == 1)
            {
                // Unlock the update, restore the start and exit
                rtfText.SelectionStart = SelectionAt;
                rtfText.SelectionLength = 0;
                LockWindowUpdate(0);
                return; // TODO: might not be correct. Was : Exit Sub
            }

            // Restore the selectionstart
            rtfText.SelectionStart = SelectionAt;
            rtfText.SelectionLength = 0;

            // Unlock the update
            LockWindowUpdate(0);
        }

        public void InitalizeKeywords()
        {
            //KeyWords[] Words = new KeyWords[13];
            Words[0].Word = "#clean";
            Words[0].Color = Color.Blue;
            Words[1].Word = "#remove";
            Words[1].Color = Color.Blue;
            Words[2].Word = "#removeall";
            Words[2].Color = Color.Blue;
            Words[3].Word = "#include";
            Words[3].Color = Color.Blue;
            Words[4].Word = "#dynamic";
            Words[4].Color = Color.Blue;
            Words[5].Word = "#org";
            Words[5].Color = Color.Blue;
            Words[6].Word = "#raw";
            Words[6].Color = Color.Blue;
            Words[7].Word = "word";
            Words[7].Color = Color.Blue;
            Words[8].Word = "end";
            Words[8].Color = Color.Blue;
            Words[9].Word = "lock";
            Words[9].Color = Color.DarkBlue;
            Words[10].Word = "faceplayer";
            Words[10].Color = Color.DarkBlue;
            Words[11].Word = "release";
            Words[11].Color = Color.DarkBlue;
            Words[12].Word = "message";
            Words[12].Color = Color.FromArgb(90, 90, 255);
            Words[13].Word = "msgbox";
            Words[13].Color = Color.FromArgb(90, 90, 255);
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            InitalizeKeywords();
            this.rtfText.Text = string.Empty;
            ColorRtb(rtfText);
        }

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Okay, now the problem/question: if there's many text in the RTB, it's going slow.
Second problem/question: if I paste text in the RTB, it only colors the last visible lines. I think it is because the 'ColorVisibleLines();'. But if I use 'ColorRtb(rtfText);' it is too slow...

Kind Regards.