/*
 * This file is part of "JTA - Telnet/SSH for the JAVA(tm) platform".
 *
 * (c) Matthias L. Jugel, Marcus Mei�ner 1996-2005. All Rights Reserved.
 *
 * Please visit http://javatelnet.org/ for updates and contact.
 *
 * --LICENSE NOTICE--
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 * --LICENSE NOTICE--
 *
 */

package de.mud.terminal;

import java.util.Arrays;

/**
 * Implementation of a Video Display Unit (VDU) buffer. This class contains
 * all methods to manipulate the buffer that stores characters and their
 * attributes as well as the regions displayed.
 *
 * @author Matthias L. Jugel, Marcus Meißner
 * @version $Id: VDUBuffer.java 503 2005-10-24 07:34:13Z marcus $
 */
public class VDUBuffer {

    /** The current version id tag */
    public final static String ID = "$Id: VDUBuffer.java 503 2005-10-24 07:34:13Z marcus $";

    /** Enable debug messages. */
    public final static int debug = 0;

    public int height, width;                          /* rows and columns */
    public boolean[] update;        /* contains the lines that need update */
    public char[][] charArray;                  /* contains the characters */
    public int[][] charAttributes;             /* contains character attrs */
    public int bufSize;
    public int maxBufSize;                                 /* buffer sizes */
    public int screenBase;                      /* the actual screen start */
    public int windowBase;                   /* where the start displaying */
    public int scrollMarker;               /* marks the last line inserted */

    private int topMargin;                               /* top scroll margin */
    private int bottomMargin;                         /* bottom scroll margin */

    // cursor variables
    protected boolean showcursor = true;
    protected int cursorX, cursorY;

    /** Scroll up when inserting a line. */
    public final static boolean SCROLL_UP = false;
    /** Scroll down when inserting a line. */
    public final static boolean SCROLL_DOWN = true;

    /*  Attributes bit-field usage:
     *
     *  8421 8421 8421 8421 8421 8421 8421 8421
     *  |||| |||| |||| |||| |||| |||| |||| |||`- Bold
     *  |||| |||| |||| |||| |||| |||| |||| ||`-- Underline
     *  |||| |||| |||| |||| |||| |||| |||| |`--- Invert
     *  |||| |||| |||| |||| |||| |||| |||| `---- Low
     *  |||| |||| |||| |||| |||| |||| |||`------ Invisible
     *  |||| |||| |||| |||| ||`+-++++-+++------- Foreground Color
     *  |||| |||| |`++-++++-++------------------ Background Color
     *  |||| |||| `----------------------------- Fullwidth character
     *  `+++-++++------------------------------- Reserved for future use
     */

    /** Make character normal. */
    public final static int NORMAL = 0x00;
    /** Make character bold. */
    public final static int BOLD = 0x01;
    /** Underline character. */
    public final static int UNDERLINE = 0x02;
    /** Invert character. */
    public final static int INVERT = 0x04;
    /** Lower intensity character. */
    public final static int LOW = 0x08;
    /** Invisible character. */
    public final static int INVISIBLE = 0x10;
    /** Unicode full-width character (CJK, et al.) */
    public final static int FULLWIDTH = 0x8000000;

    /** how much to left shift the foreground color */
    public final static int COLOR_FG_SHIFT = 5;
    /** how much to left shift the background color */
    public final static int COLOR_BG_SHIFT = 14;
    /** color mask */
    public final static int COLOR = 0x7fffe0;    /* 0000 0000 0111 1111 1111 1111 1110 0000 */
    /** foreground color mask */
    public final static int COLOR_FG = 0x3fe0;   /* 0000 0000 0000 0000 0011 1111 1110 0000 */
    /** background color mask */
    public final static int COLOR_BG = 0x7fc000; /* 0000 0000 0111 1111 1100 0000 0000 0000 */

    /**
     * Create a new video display buffer with the passed width and height in
     * characters.
     * @param width the length of the character lines
     * @param height the amount of lines on the screen
     */
    public VDUBuffer(int width, int height) {
        // set the display screen size
        setScreenSize(width, height, false);
    }

    /**
     * Create a standard video display buffer with 80 columns and 24 lines.
     */
    public VDUBuffer() {
        this(80, 24);
    }

    /**
     * Put a character on the screen with normal font and outline.
     * The character previously on that position will be overwritten.
     * You need to call redraw() to update the screen.
     * @param c x-coordinate (column)
     * @param l y-coordinate (line)
     * @param ch the character to show on the screen
     * @see #insertChar
     * @see #deleteChar
     * @see #redraw
     */
    public void putChar(int c, int l, char ch) {
        putChar(c, l, ch, NORMAL);
    }

    /**
     * Put a character on the screen with specific font and outline.
     * The character previously on that position will be overwritten.
     * You need to call redraw() to update the screen.
     * @param c x-coordinate (column)
     * @param l y-coordinate (line)
     * @param ch the character to show on the screen
     * @param attributes the character attributes
     * @see #BOLD
     * @see #UNDERLINE
     * @see #INVERT
     * @see #INVISIBLE
     * @see #NORMAL
     * @see #LOW
     * @see #insertChar
     * @see #deleteChar
     * @see #redraw
     */

    public void putChar(int c, int l, char ch, int attributes) {
        charArray[screenBase + l][c] = ch;
        charAttributes[screenBase + l][c] = attributes;

        if (l < height)
            update[l + 1] = true;
    }

    /**
     * Get the character at the specified position.
     * @param c x-coordinate (column)
     * @param l y-coordinate (line)
     * @see #putChar
     */
    public char getChar(int c, int l) {
        return charArray[screenBase + l][c];
    }

    /**
     * Get the attributes for the specified position.
     * @param c x-coordinate (column)
     * @param l y-coordinate (line)
     * @see #putChar
     */
    public int getAttributes(int c, int l) {
        return charAttributes[screenBase + l][c];
    }

    /**
     * Insert a character at a specific position on the screen.
     * All character right to from this position will be moved one to the right.
     * You need to call redraw() to update the screen.
     * @param c x-coordinate (column)
     * @param l y-coordinate (line)
     * @param ch the character to insert
     * @param attributes the character attributes
     * @see #BOLD
     * @see #UNDERLINE
     * @see #INVERT
     * @see #INVISIBLE
     * @see #NORMAL
     * @see #LOW
     * @see #putChar
     * @see #deleteChar
     * @see #redraw
     */
    public void insertChar(int c, int l, char ch, int attributes) {
        System.arraycopy(charArray[screenBase + l], c,
                         charArray[screenBase + l], c + 1, width - c - 1);
        System.arraycopy(charAttributes[screenBase + l], c,
                         charAttributes[screenBase + l], c + 1, width - c - 1);
        putChar(c, l, ch, attributes);
    }

    /**
     * Delete a character at a given position on the screen.
     * All characters right to the position will be moved one to the left.
     * You need to call redraw() to update the screen.
     * @param c x-coordinate (column)
     * @param l y-coordinate (line)
     * @see #putChar
     * @see #insertChar
     * @see #redraw
     */
    public void deleteChar(int c, int l) {
        if (c < width - 1) {
            System.arraycopy(charArray[screenBase + l], c + 1,
                             charArray[screenBase + l], c, width - c - 1);
            System.arraycopy(charAttributes[screenBase + l], c + 1,
                             charAttributes[screenBase + l], c, width - c - 1);
        }

        putChar(width - 1, l, (char) 0);
    }

    /**
     * Put a String at a specific position. Any characters previously on that
     * position will be overwritten. You need to call redraw() for screen update.
     * @param c x-coordinate (column)
     * @param l y-coordinate (line)
     * @param s the string to be shown on the screen
     * @see #BOLD
     * @see #UNDERLINE
     * @see #INVERT
     * @see #INVISIBLE
     * @see #NORMAL
     * @see #LOW
     * @see #putChar
     * @see #insertLine
     * @see #deleteLine
     * @see #redraw
     */
    public void putString(int c, int l, String s) {
        putString(c, l, s, NORMAL);
    }

    /**
     * Put a String at a specific position giving all characters the same
     * attributes. Any characters previously on that position will be
     * overwritten. You need to call redraw() to update the screen.
     * @param c x-coordinate (column)
     * @param l y-coordinate (line)
     * @param s the string to be shown on the screen
     * @param attributes character attributes
     * @see #BOLD
     * @see #UNDERLINE
     * @see #INVERT
     * @see #INVISIBLE
     * @see #NORMAL
     * @see #LOW
     * @see #putChar
     * @see #insertLine
     * @see #deleteLine
     * @see #redraw
     */
    public void putString(int c, int l, String s, int attributes) {
        for (int i = 0; i < s.length() && c + i < width; i++)
            putChar(c + i, l, s.charAt(i), attributes);
    }

    /**
     * Insert a blank line at a specific position.
     * The current line and all previous lines are scrolled one line up. The
     * top line is lost. You need to call redraw() to update the screen.
     * @param l the y-coordinate to insert the line
     * @see #deleteLine
     * @see #redraw
     */
    public void insertLine(int l) {
        insertLine(l, 1, SCROLL_UP);
    }

    /**
     * Insert blank lines at a specific position.
     * You need to call redraw() to update the screen
     * @param l the y-coordinate to insert the line
     * @param n amount of lines to be inserted
     * @see #deleteLine
     * @see #redraw
     */
    public void insertLine(int l, int n) {
        insertLine(l, n, SCROLL_UP);
    }

    /**
     * Insert a blank line at a specific position. Scroll text according to
     * the argument.
     * You need to call redraw() to update the screen
     * @param l the y-coordinate to insert the line
     * @param scrollDown scroll down
     * @see #deleteLine
     * @see #SCROLL_UP
     * @see #SCROLL_DOWN
     * @see #redraw
     */
    public void insertLine(int l, boolean scrollDown) {
        insertLine(l, 1, scrollDown);
    }

    /**
     * Insert blank lines at a specific position.
     * The current line and all previous lines are scrolled one line up. The
     * top line is lost. You need to call redraw() to update the screen.
     * @param l the y-coordinate to insert the line
     * @param n number of lines to be inserted
     * @param scrollDown scroll down
     * @see #deleteLine
     * @see #SCROLL_UP
     * @see #SCROLL_DOWN
     * @see #redraw
     */

    public synchronized void insertLine(int l, int n, boolean scrollDown) {
        char cbuf[][] = null;
        int abuf[][] = null;
        int offset = 0;
        int oldBase = screenBase;
        int newScreenBase = screenBase;
        int newWindowBase = windowBase;
        int newBufSize = bufSize;

        if (l > bottomMargin) /* We do not scroll below bottom margin (below the scrolling region). */
            return;

        int top = (l < topMargin ?
                   0 : (l > bottomMargin ?
                        (bottomMargin + 1 < height ?
                         bottomMargin + 1 : height - 1) : topMargin));
        int bottom = (l > bottomMargin ?
                      height - 1 : (l < topMargin ?
                                    (topMargin > 0 ?
                                     topMargin - 1 : 0) : bottomMargin));

        // System.out.println("l is "+l+", top is "+top+", bottom is "+bottom+", bottomargin is "+bottomMargin+", topMargin is "+topMargin);
        if (scrollDown) {
            if (n > (bottom - top)) n = (bottom - top);

            int size = bottom - l - (n - 1);

            if (size < 0) size = 0;

            cbuf = new char[size][];
            abuf = new int[size][];
            System.arraycopy(charArray, oldBase + l, cbuf, 0, bottom - l - (n - 1));
            System.arraycopy(charAttributes, oldBase + l,
                             abuf, 0, bottom - l - (n - 1));
            System.arraycopy(cbuf, 0, charArray, oldBase + l + n,
                             bottom - l - (n - 1));
            System.arraycopy(abuf, 0, charAttributes, oldBase + l + n,
                             bottom - l - (n - 1));
            cbuf = charArray;
            abuf = charAttributes;
        }
        else {
            try {
                if (n > (bottom - top) + 1) n = (bottom - top) + 1;

                if (bufSize < maxBufSize) {
                    if (bufSize + n > maxBufSize) {
                        offset = n - (maxBufSize - bufSize);
                        scrollMarker += offset;
                        newBufSize = maxBufSize;
                        newScreenBase = maxBufSize - height - 1;
                        newWindowBase = screenBase;
                    }
                    else {
                        scrollMarker += n;
                        newScreenBase += n;
                        newWindowBase += n;
                        newBufSize += n;
                    }

                    cbuf = new char[newBufSize][];
                    abuf = new int[newBufSize][];
                }
                else {
                    offset = n;
                    cbuf = charArray;
                    abuf = charAttributes;
                }

                // copy anything from the top of the buffer (+offset) to the new top
                // up to the screenBase.
                if (oldBase > 0) {
                    System.arraycopy(charArray, offset,
                                     cbuf, 0,
                                     oldBase - offset);
                    System.arraycopy(charAttributes, offset,
                                     abuf, 0,
                                     oldBase - offset);
                }

                // copy anything from the top of the screen (screenBase) up to the
                // topMargin to the new screen
                if (top > 0) {
                    System.arraycopy(charArray, oldBase,
                                     cbuf, newScreenBase,
                                     top);
                    System.arraycopy(charAttributes, oldBase,
                                     abuf, newScreenBase,
                                     top);
                }

                // copy anything from the topMargin up to the amount of lines inserted
                // to the gap left over between scrollback buffer and screenBase
                if (oldBase >= 0) {
                    System.arraycopy(charArray, oldBase + top,
                                     cbuf, oldBase - offset,
                                     n);
                    System.arraycopy(charAttributes, oldBase + top,
                                     abuf, oldBase - offset,
                                     n);
                }

                // copy anything from topMargin + n up to the line linserted to the
                // topMargin
                System.arraycopy(charArray, oldBase + top + n,
                                 cbuf, newScreenBase + top,
                                 l - top - (n - 1));
                System.arraycopy(charAttributes, oldBase + top + n,
                                 abuf, newScreenBase + top,
                                 l - top - (n - 1));

                //
                // copy the all lines next to the inserted to the new buffer
                if (l < height - 1) {
                    System.arraycopy(charArray, oldBase + l + 1,
                                     cbuf, newScreenBase + l + 1,
                                     (height - 1) - l);
                    System.arraycopy(charAttributes, oldBase + l + 1,
                                     abuf, newScreenBase + l + 1,
                                     (height - 1) - l);
                }
            }
            catch (ArrayIndexOutOfBoundsException e) {
                // this should not happen anymore, but I will leave the code
                // here in case something happens anyway. That code above is
                // so complex I always have a hard time understanding what
                // I did, even though there are comments
                System.err.println("*** Error while scrolling up:");
                System.err.println("--- BEGIN STACK TRACE ---");
                e.printStackTrace();
                System.err.println("--- END STACK TRACE ---");
                System.err.println("bufSize=" + bufSize + ", maxBufSize=" + maxBufSize);
                System.err.println("top=" + top + ", bottom=" + bottom);
                System.err.println("n=" + n + ", l=" + l);
                System.err.println("screenBase=" + screenBase + ", windowBase=" + windowBase);
                System.err.println("newScreenBase=" + newScreenBase + ", newWindowBase=" + newWindowBase);
                System.err.println("oldBase=" + oldBase);
                System.err.println("size.width=" + width + ", size.height=" + height);
                System.err.println("abuf.length=" + abuf.length + ", cbuf.length=" + cbuf.length);
                System.err.println("*** done dumping debug information");
            }
        }

        // this is a little helper to mark the scrolling
        scrollMarker -= n;

        for (int i = 0; i < n; i++) {
            cbuf[(newScreenBase + l) + (scrollDown ? i : -i)] = new char[width];
            Arrays.fill(cbuf[(newScreenBase + l) + (scrollDown ? i : -i)], ' ');
            abuf[(newScreenBase + l) + (scrollDown ? i : -i)] = new int[width];
        }

        charArray = cbuf;
        charAttributes = abuf;
        screenBase = newScreenBase;
        windowBase = newWindowBase;
        bufSize = newBufSize;

        if (scrollDown)
            markLine(l, bottom - l + 1);
        else
            markLine(top, l - top + 1);

        display.updateScrollBar();
    }

    /**
     * Delete a line at a specific position. Subsequent lines will be scrolled
     * up to fill the space and a blank line is inserted at the end of the
     * screen.
     * @param l the y-coordinate to insert the line
     * @see #deleteLine
     */
    public void deleteLine(int l) {
        int bottom = (l > bottomMargin ? height - 1 :
                      (l < topMargin ? topMargin : bottomMargin + 1));
        int numRows = bottom - l - 1;
        char[] discardedChars = charArray[screenBase + l];
        int[] discardedAttributes = charAttributes[screenBase + l];

        if (numRows > 0) {
            System.arraycopy(charArray, screenBase + l + 1,
                             charArray, screenBase + l, numRows);
            System.arraycopy(charAttributes, screenBase + l + 1,
                             charAttributes, screenBase + l, numRows);
        }

        int newBottomRow = screenBase + bottom - 1;
        charArray[newBottomRow] = discardedChars;
        charAttributes[newBottomRow] = discardedAttributes;
        Arrays.fill(charArray[newBottomRow], ' ');
        Arrays.fill(charAttributes[newBottomRow], 0);
        markLine(l, bottom - l);
    }

    /**
     * Delete a rectangular portion of the screen.
     * You need to call redraw() to update the screen.
     * @param c x-coordinate (column)
     * @param l y-coordinate (row)
     * @param w with of the area in characters
     * @param h height of the area in characters
     * @param curAttr attribute to fill
     * @see #deleteChar
     * @see #deleteLine
     * @see #redraw
     */
    public void deleteArea(int c, int l, int w, int h, int curAttr) {
        int endColumn = c + w;
        int targetRow = screenBase + l;

        for (int i = 0; i < h && l + i < height; i++) {
            Arrays.fill(charAttributes[targetRow], c, endColumn, curAttr);
            Arrays.fill(charArray[targetRow], c, endColumn, ' ');
            targetRow++;
        }

        markLine(l, h);
    }

    /**
     * Delete a rectangular portion of the screen.
     * You need to call redraw() to update the screen.
     * @param c x-coordinate (column)
     * @param l y-coordinate (row)
     * @param w with of the area in characters
     * @param h height of the area in characters
     * @see #deleteChar
     * @see #deleteLine
     * @see #redraw
     */
    public void deleteArea(int c, int l, int w, int h) {
        deleteArea(c, l, w, h, 0);
    }

    /**
     * Sets whether the cursor is visible or not.
     * @param doshow
     */
    public void showCursor(boolean doshow) {
        showcursor = doshow;
    }

    /**
     * Check whether the cursor is currently visible.
     * @return visibility
     */
    public boolean isCursorVisible() {
        return showcursor;
    }

    /**
     * Puts the cursor at the specified position.
     * @param c column
     * @param l line
     */
    public void setCursorPosition(int c, int l) {
        cursorX = c;
        cursorY = l;
    }

    /**
     * Get the current column of the cursor position.
     */
    public int getCursorColumn() {
        return cursorX;
    }

    /**
     * Get the current line of the cursor position.
     */
    public int getCursorRow() {
        return cursorY;
    }

    /**
     * Set the current window base. This allows to view the scrollback buffer.
     * @param line the line where the screen window starts
     * @see #setBufferSize
     * @see #getBufferSize
     */
    public void setWindowBase(int line) {
        if (line > screenBase)
            line = screenBase;
        else if (line < 0) line = 0;

        windowBase = line;
        update[0] = true;
        redraw();
    }

    /**
     * Get the current window base.
     * @see #setWindowBase
     */
    public int getWindowBase() {
        return windowBase;
    }

    /**
     * Set the scroll margins simultaneously.  If they're out of bounds, trim them.
     * @param l1 line that is the top
     * @param l2 line that is the bottom
     */
    public void setMargins(int l1, int l2) {
        if (l1 > l2)
            return;

        if (l1 < 0)
            l1 = 0;

        if (l2 >= height)
            l2 = height - 1;

        topMargin = l1;
        bottomMargin = l2;
    }

    /**
     * Set the top scroll margin for the screen. If the current bottom margin
     * is smaller it will become the top margin and the line will become the
     * bottom margin.
     * @param l line that is the margin
     */
    public void setTopMargin(int l) {
        if (l > bottomMargin) {
            topMargin = bottomMargin;
            bottomMargin = l;
        }
        else
            topMargin = l;

        if (topMargin < 0) topMargin = 0;

        if (bottomMargin >= height) bottomMargin = height - 1;
    }

    /**
     * Get the top scroll margin.
     */
    public int getTopMargin() {
        return topMargin;
    }

    /**
     * Set the bottom scroll margin for the screen. If the current top margin
     * is bigger it will become the bottom margin and the line will become the
     * top margin.
     * @param l line that is the margin
     */
    public void setBottomMargin(int l) {
        if (l < topMargin) {
            bottomMargin = topMargin;
            topMargin = l;
        }
        else
            bottomMargin = l;

        if (topMargin < 0) topMargin = 0;

        if (bottomMargin >= height) bottomMargin = height - 1;
    }

    /**
     * Get the bottom scroll margin.
     */
    public int getBottomMargin() {
        return bottomMargin;
    }

    /**
     * Set scrollback buffer size.
     * @param amount new size of the buffer
     */
    public void setBufferSize(int amount) {
        if (amount < height) amount = height;

        if (amount < maxBufSize) {
            char cbuf[][] = new char[amount][width];
            int abuf[][] = new int[amount][width];
            int copyStart = bufSize - amount < 0 ? 0 : bufSize - amount;
            int copyCount = bufSize - amount < 0 ? bufSize : amount;

            if (charArray != null)
                System.arraycopy(charArray, copyStart, cbuf, 0, copyCount);

            if (charAttributes != null)
                System.arraycopy(charAttributes, copyStart, abuf, 0, copyCount);

            charArray = cbuf;
            charAttributes = abuf;
            bufSize = copyCount;
            screenBase = bufSize - height;
            windowBase = screenBase;
        }

        maxBufSize = amount;
        update[0] = true;
        redraw();
    }

    /**
     * Retrieve current scrollback buffer size.
     * @see #setBufferSize
     */
    public int getBufferSize() {
        return bufSize;
    }

    /**
     * Retrieve maximum buffer Size.
     * @see #getBufferSize
     */
    public int getMaxBufferSize() {
        return maxBufSize;
    }

    /**
     * Change the size of the screen. This will include adjustment of the
     * scrollback buffer.
     * @param w of the screen
     * @param h of the screen
     */
    public void setScreenSize(int w, int h, boolean broadcast) {
        char cbuf[][];
        int abuf[][];
        int maxSize = bufSize;

        if (w < 1 || h < 1) return;

        if (debug > 0)
            System.err.println("VDU: screen size [" + w + "," + h + "]");

        if (h > maxBufSize)
            maxBufSize = h;

        if (h > bufSize) {
            bufSize = h;
            screenBase = 0;
            windowBase = 0;
        }

        if (windowBase + h >= bufSize)
            windowBase = bufSize - h;

        if (screenBase + h >= bufSize)
            screenBase = bufSize - h;

        cbuf = new char[bufSize][w];
        abuf = new int[bufSize][w];

        for (int i = 0; i < bufSize; i++) {
            Arrays.fill(cbuf[i], ' ');
        }

        if (bufSize < maxSize)
            maxSize = bufSize;

        int rowLength;

        if (charArray != null && charAttributes != null) {
            for (int i = 0; i < maxSize && charArray[i] != null; i++) {
                rowLength = charArray[i].length;
                System.arraycopy(charArray[i], 0, cbuf[i], 0,
                                 w < rowLength ? w : rowLength);
                System.arraycopy(charAttributes[i], 0, abuf[i], 0,
                                 w < rowLength ? w : rowLength);
            }
        }

        int C = getCursorColumn();

        if (C < 0)
            C = 0;
        else if (C >= width)
            C = width - 1;

        int R = getCursorRow();

        if (R < 0)
            R = 0;
        else if (R >= height)
            R = height - 1;

        setCursorPosition(C, R);
        charArray = cbuf;
        charAttributes = abuf;
        width = w;
        height = h;
        topMargin = 0;
        bottomMargin = h - 1;
        update = new boolean[h + 1];
        update[0] = true;
        /*  FIXME: ???
        if(resizeStrategy == RESIZE_FONT)
          setBounds(getBounds());
        */
    }

    /**
     * Get amount of rows on the screen.
     */
    public int getRows() {
        return height;
    }

    /**
     * Get amount of columns on the screen.
     */
    public int getColumns() {
        return width;
    }

    /**
     * Mark lines to be updated with redraw().
     * @param l starting line
     * @param n amount of lines to be updated
     * @see #redraw
     */
    public void markLine(int l, int n) {
        for (int i = 0; (i < n) && (l + i < height); i++)
            update[l + i + 1] = true;
    }

//  private static int checkBounds(int value, int lower, int upper) {
//    if (value < lower)
//      return lower;
//    else if (value > upper)
//      return upper;
//    else
//      return value;
//  }

    /** a generic display that should redraw on demand */
    protected VDUDisplay display;

    public void setDisplay(VDUDisplay display) {
        this.display = display;
    }

    /**
     * Trigger a redraw on the display.
     */
    protected void redraw() {
        if (display != null)
            display.redraw();
    }
}