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RSyntaxTextArea is the syntax highlighting text editor for Swing applications. Features include syntax highlighting for 40+ languages, code folding, code completion, regex find and replace, macros, code templates, undo/redo, line numbering and bracket matching.
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/*
 * 10/01/2009
 *
 * SmartHighlightPainter.java - A highlight painter whose rendered highlights
 * don't "grow" when the user appends text to the end of them.
 *
 * This library is distributed under a modified BSD license.  See the included
 * LICENSE file for details.
 */
package org.fife.ui.rtextarea;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Paint;
import java.awt.Rectangle;
import java.awt.Shape;

import javax.swing.text.BadLocationException;
import javax.swing.text.JTextComponent;
import javax.swing.text.Position;
import javax.swing.text.View;


/**
 * A "smart" highlight painter designed for use in RSyntaxTextArea.  Adds the
 * following features:
 *
 * 
 *    Rendered highlights don't "grow" when users append text to the "end"
 *        of them.  This is implemented by assuming that the highlights
 *        themselves specify their end offset as one offset "too short".  This
 *        behavior is baked into various RSTA highlights (mark all, mark
 *        occurrences, etc.).
 *    
Ability to paint a border line around highlights.
 * 
 *
 * @author Robert Futrell
 * @version 1.0
 */
public class SmartHighlightPainter extends ChangeableHighlightPainter {

	/**
	 * The default highlight color.
	 */
	public static final Color DEFAULT_HIGHLIGHT_COLOR = Color.LIGHT_GRAY;

	private Color borderColor;
	private boolean paintBorder;


	/**
	 * Creates a highlight painter using a default color.
	 */
	public SmartHighlightPainter() {
		super(DEFAULT_HIGHLIGHT_COLOR);
	}


	/**
	 * Constructor.
	 *
	 * @param paint The color or paint to use for this painter.
	 */
	public SmartHighlightPainter(Paint paint) {
		super(paint);
	}


	/**
	 * Returns whether a border is painted around marked occurrences.
	 *
	 * @return Whether a border is painted.
	 * @see #setPaintBorder(boolean)
	 * @see #getPaint()
	 */
	public boolean getPaintBorder() {
		return paintBorder;
	}


	@Override
	public Shape paintLayer(Graphics g, int p0, int p1, Shape viewBounds,
								JTextComponent c, View view) {

		g.setColor((Color)getPaint());
System.out.println("... SmartHighlightPainter: rendering: " + p0 + " - " + p1);
		// This special case isn't needed for most standard Swing Views (which
		// always return a width of 1 for modelToView() calls), but it is
		// needed for RSTA views, which actually return the width of chars for
		// modelToView calls.  But this should be faster anyway, as we
		// short-circuit and do only one modelToView() for one offset.
		if (p0==p1) {
			try {
				Shape s = view.modelToView(p0, viewBounds,
											Position.Bias.Forward);
				Rectangle r = s.getBounds();
				g.drawLine(r.x, r.y, r.x, r.y+r.height);
				return r;
			} catch (BadLocationException ble) {
				ble.printStackTrace(); // Never happens
				return null;
			}
		}

		// Occurs in word wrap mode only.  Mark an occurrence that ends at the
		// last offset in the document, then hit backspace.  That last marked
		// occurrence will fill the entire viewport's height until repainted
		// 1 second later.  To avoid this, short-circuit if a highlight
		// being painted has an offset past the document length.
		// https://github.com/bobbylight/RSyntaxTextArea/issues/149
		p1 = Math.min(p1, c.getDocument().getLength());

		if (p0 == view.getStartOffset() && p1 == view.getEndOffset()) {

			// Contained in view, can just use bounds.
			Rectangle alloc;
			if (viewBounds instanceof Rectangle) {
				alloc = (Rectangle) viewBounds;
			} else {
				alloc = viewBounds.getBounds();
			}
			g.fillRect(alloc.x, alloc.y, alloc.width, alloc.height);
			return alloc;
		}

		// Should only render part of View.
		try {
			// --- determine locations ---
			Shape shape = view.modelToView(p0, Position.Bias.Forward, p1,
					Position.Bias.Backward, viewBounds);
			Rectangle r = shape instanceof Rectangle ? (Rectangle) shape :
														shape.getBounds();
			g.fillRect(r.x, r.y, r.width, r.height);
			if (paintBorder) {
				g.setColor(borderColor);
				g.drawRect(r.x,r.y, r.width-1,r.height-1);
			}
			return r;
		} catch (BadLocationException e) { // Never happens
			e.printStackTrace();
			return null;
		}

	}


	@Override
	public void setPaint(Paint paint) {
		super.setPaint(paint);
		if (paint instanceof Color) {
			borderColor = ((Color)paint).darker();
		}
	}


	/**
	 * Toggles whether a border is painted around highlights.
	 *
	 * @param paint Whether to paint a border.
	 * @see #getPaintBorder()
	 * @see #setPaint(Paint)
	 */
	public void setPaintBorder(boolean paint) {
		this.paintBorder = paint;
	}


}