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A Java API for Meta-CSP based reasoning
There is a newer version: 1.3.5
package org.metacsp.utility.logging;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.Shape;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

import javax.swing.SwingUtilities;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.Element;
import javax.swing.text.Highlighter;
import javax.swing.text.JTextComponent;

/*
 *  Track the movement of the Caret by painting a background line at the
 *  current caret position.
 */
public class LinePainter implements Highlighter.HighlightPainter, CaretListener, MouseListener, MouseMotionListener {
	protected JTextComponent component;
	private Color color;
	private Rectangle lastView;
	private int currentLine = 0;
	
	/*
	 *  The line color will be calculated automatically by attempting
	 *  to make the current selection lighter by a factor of 1.2.
	 *
	 *  @param component  text component that requires background line painting
	 */
	public LinePainter(JTextComponent component)
	{
		this(component, null);
		setLighter(component.getSelectionColor());
	}

	/*
	 *  Manually control the line color
	 *
	 *  @param component  text component that requires background line painting
	 *  @param color      the color of the background line
	 */
	public LinePainter(JTextComponent component, Color color)
	{
		this.component = component;
		setColor( color );

		//  Add listeners so we know when to change highlighting
		component.addCaretListener( this );
		component.addMouseListener( this );
		component.addMouseMotionListener( this );

		//  Turn highlighting on by adding a dummy highlight
		try {
			component.getHighlighter().addHighlight(0, 0, this);
		}
		catch(BadLocationException ble) {}
	}

	public int getCurrentLine() {
		return currentLine;
	}
	
	/*
	 *	You can reset the line color at any time
	 *
	 *  @param color  the color of the background line
	 */
	public void setColor(Color color)
	{
		this.color = color;
	}

	/*
	 *  Calculate the line color by making the selection color lighter
	 *
	 *  @return the color of the background line
	 */
	public void setLighter(Color color)
	{
		int red   = Math.min(255, (int)(color.getRed() * 1.2));
		int green = Math.min(255, (int)(color.getGreen() * 1.2));
		int blue  = Math.min(255, (int)(color.getBlue() * 1.2));
		setColor(new Color(red, green, blue));
	}

	//  Paint the background highlight

	public void paint(Graphics g, int p0, int p1, Shape bounds, JTextComponent c)
	{
		try
		{
			Rectangle r = c.modelToView(c.getCaretPosition());
			g.setColor( color );
			g.fillRect(0, r.y, c.getWidth(), r.height);

			if (lastView == null)
				lastView = r;
		}
		catch(BadLocationException ble) {System.out.println(ble);}
	}

	/*
	 *   Caret position has changed, remove the highlight
	 */
	private void resetHighlight()
	{
		//  Use invokeLater to make sure updates to the Document are completed,
		//  otherwise Undo processing causes the modelToView method to loop.

		SwingUtilities.invokeLater(new Runnable()
		{
			public void run()
			{
				try
				{
					int offset =  component.getCaretPosition();
					Rectangle currentView = component.modelToView(offset);

					//  Remove the highlighting from the previously highlighted line

					if (lastView != null && lastView.y != currentView.y)
					{
						component.repaint(0, lastView.y, component.getWidth(), lastView.height);
						lastView = currentView;
					}
				}
				catch(BadLocationException ble) {}
			}
		});
	}

	//  Implement CaretListener

	public void caretUpdate(CaretEvent e)
	{
		resetHighlight();
		try {
			this.currentLine = getLineOfOffset(e.getDot());
			//System.out.println(getCurrentLine());
		}
		catch (BadLocationException e1) { e1.printStackTrace(); }
				
		//int line = getLineOfOffset(tp, dot);
	    //int positionInLine = dot - getLineStartOffset(tp, line);
	}

	//  Implement MouseListener

	public void mousePressed(MouseEvent e)
	{
		resetHighlight();
	}

	public void mouseClicked(MouseEvent e) {}
	public void mouseEntered(MouseEvent e) {}
	public void mouseExited(MouseEvent e) {}
	public void mouseReleased(MouseEvent e) {}

	//  Implement MouseMotionListener

	public void mouseDragged(MouseEvent e)
	{
		resetHighlight();
	}

	public void mouseMoved(MouseEvent e) {}

	public int getLineOfOffset(int offset) throws BadLocationException {
		Document doc = component.getDocument();
		if (offset < 0) {
			throw new BadLocationException("Can't translate offset to line", -1);
		} else if (offset > doc.getLength()) {
			throw new BadLocationException("Can't translate offset to line", doc.getLength() + 1);
		} else {
			Element map = doc.getDefaultRootElement();
			return map.getElementIndex(offset);
		}
	}

	public int getLineStartOffset(int line) throws BadLocationException {
		Element map = component.getDocument().getDefaultRootElement();
		if (line < 0) {
			throw new BadLocationException("Negative line", -1);
		} else if (line >= map.getElementCount()) {
			throw new BadLocationException("No such line", component.getDocument().getLength() + 1);
		} else {
			Element lineElem = map.getElement(line);
			return lineElem.getStartOffset();
		}
	}
}