gcc/libjava/classpath/javax/swing/border/LineBorder.java

/* LineBorder.java --
   Copyright (C) 2003 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath 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, or (at your option)
any later version.

GNU Classpath 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.

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02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package javax.swing.border;

import java.awt.Color;
import java.awt.Component;
import java.awt.Graphics;
import java.awt.Insets;


/**
 * A border that consists of a line whose thickness and color can be
 * specified. There also is a variant with rounded corners.
 *
 * @author Sascha Brawer (brawer@dandelis.ch)
 */
public class LineBorder extends AbstractBorder
{
  /**
   * Determined using the <code>serialver</code> tool
   * of Apple/Sun JDK 1.3.1 on MacOS X 10.1.5.
   */
  static final long serialVersionUID = -787563427772288970L;


  /**
   * A shared instance of a black, one pixel thick, plain LineBorder.
   * The singleton object is lazily created by {@link
   * #createBlackLineBorder()} upon its first invocation.
   */
  private static LineBorder blackLineBorder;


  /**
   * A shared instance of a gray, one pixel thick, plain LineBorder.
   * The singleton object is lazily created by {@link
   * #createGrayLineBorder()} upon its first invocation.
   */
  private static LineBorder grayLineBorder;


  /**
   * The width of the line in pixels.
   */
  protected int thickness;


  /**
   * The color of the line.
   */
  protected Color lineColor;


  /**
   * Indicates whether the line is drawn with rounded corners
   * (<code>true</code>) or not ((<code>false</code>).
   */
  protected boolean roundedCorners;


  /**
   * Constructs a LineBorder given its color.  The border will be one
   * pixel thick and have plain corners.
   *
   * @param color the color for drawing the border.
   *
   * @see #LineBorder(java.awt.Color, int, boolean)
   */
  public LineBorder(Color color)
  {
    this(color, /* thickness */ 1, /* roundedCorners */ false);
  }


  /**
   * Constructs a LineBorder given its color and thickness.  The
   * border will have plain corners.
   *
   * @param color the color for drawing the border.
   * @param thickness the width of the line in pixels.
   *
   * @see #LineBorder(java.awt.Color, int, boolean)
   */
  public LineBorder(Color color, int thickness)
  {
    this (color, thickness, /* roundedCorners */ false);
  }


  /**
   * Constructs a LineBorder given its color, thickness, and whether
   * it has rounded corners.
   *
   * <p><img src="doc-files/LineBorder-1.png" width="500" height="200"
   * alt="[An illustration of two LineBorders]" />
   *
   * <p>Note that the enlarged view in the right-hand picture shows
   * that the implementation draws one more pixel than specified,
   * provided that <code>roundedCorders</code> is <code>true</code>
   * and anti-aliasing is turned on while painting. While this might
   * be considered a bug, the Sun reference implementation (at least
   * JDK 1.3.1 on Apple MacOS X 10.1.5) can be observed to fill
   * exactly the same pixels as shown above. The GNU Classpath
   * LineBorder replicates the observed behavior of the Sun
   * implementation.
   *
   * @param color the color for drawing the border.
   * @param thickness the width of the line in pixels.
   * @param roundedCorners <code>true</code> for rounded corners,
   *        <code>false</code> for plain corners.
   *
   * @since 1.3
   */
  // For the bug mentioned in the JavaDoc, please see also the comment
  // in the paintBorder method below.
  //
  public LineBorder(Color color, int thickness, boolean roundedCorners)
  {
    if ((color == null) || (thickness < 0))
      throw new IllegalArgumentException();

    this.lineColor = color;
    this.thickness = thickness;
    this.roundedCorners = roundedCorners;
  }


  /**
   * Returns a black, one pixel thick, plain {@link LineBorder}. The method
   * may always return the same (singleton) {@link LineBorder} instance.
   *
   * @return The border.
   */
  public static Border createBlackLineBorder()
  {
    /* Swing is not designed to be thread-safe, so there is no
     * need to synchronize the access to the global variable.
     */
    if (blackLineBorder == null)
      blackLineBorder = new LineBorder(Color.black);

    return blackLineBorder;
  }


  /**
   * Returns a gray, one pixel thick, plain {@link LineBorder}. The method
   * may always return the same (singleton) {@link LineBorder} instance.
   *
   * @return The border.
   */
  public static Border createGrayLineBorder()
  {
    /* Swing is not designed to be thread-safe, so there is no
     * need to synchronize the access to the global variable.
     */
    if (grayLineBorder == null)
      grayLineBorder = new LineBorder(Color.gray);

    return grayLineBorder;
  }


  /**
   * Paints the line border around a given Component.
   *
   * @param c the component whose border is to be painted.
   * @param g the graphics for painting.
   * @param x the horizontal position for painting the border.
   * @param y the vertical position for painting the border.
   * @param width the width of the available area for painting the border.
   * @param height the height of the available area for painting the border.
   */
  public void paintBorder(Component c, Graphics  g,
                          int x, int y, int width, int height)
  {
    Color oldColor = g.getColor();

    try
    {
      g.setColor(lineColor);

      // If width and height were not adjusted, the border would
      // appear one pixel too large in both directions.
      width -= 1;
      height -= 1;

      // Blurred, too large appearance
      // -----------------------------
      // While Java 2D has introduced line strokes of arbitrary width,
      // it seems desirable to keep this code independent of Java 2D.
      // Therefore, multiple nested rectangles (or rounded rectangles)
      // are drawn in order to simulate a line whose thickness is
      // greater than one pixel.
      //
      // This hack causes a blurred appearance when anti-aliasing is
      // on. Interestingly enough, though, the Sun JDK 1.3.1 (at least
      // on MacOS X 10.1.5) shows exactly the same appearance under
      // this condition. It thus seems likely that Sun does the same
      // hack for simulating thick lines.  For this reason, the
      // blurred appearance seems acceptable -- especially since GNU
      // Classpath tries to be compatible with the Sun reference
      // implementation.
      for (int i = 0; i < thickness; i++)
      {
        if (roundedCorners)
          g.drawRoundRect(x, y, width, height, thickness, thickness);
        else
          g.drawRect(x, y, width, height);

        x += 1;
        y += 1;
        width -= 2;
        height -= 2;
      }
    }
    finally
    {
      g.setColor(oldColor);
    }
  }


  /**
   * Measures the width of this border.
   *
   * @param c the component whose border is to be measured.
   *
   * @return an Insets object whose <code>left</code>, <code>right</code>,
   *         <code>top</code> and <code>bottom</code> fields indicate the
   *         width of the border at the respective edge, which is the
   *         thickness of the line.
   *
   * @see #getBorderInsets(java.awt.Component, java.awt.Insets)
   */
  public Insets getBorderInsets(Component c)
  {
    return new Insets(thickness, thickness, thickness, thickness);
  }


  /**
   * Measures the width of this border, storing the results into a
   * pre-existing Insets object.
   *
   * @param insets an Insets object for holding the result values.
   *        After invoking this method, the <code>left</code>,
   *        <code>right</code>, <code>top</code> and
   *        <code>bottom</code> fields indicate the width of the
   *        border at the respective edge, which is the thickness
   *        of the line.
   *
   * @return the same object that was passed for <code>insets</code>.
   *
   * @see #getBorderInsets(Component)
   */
  public Insets getBorderInsets(Component c, Insets insets)
  {
    insets.left = insets.right = insets.top = insets.bottom = thickness;
    return insets;
  }


  /**
   * Returns the color of the line.
   *
   * @return The line color (never <code>null</code>).
   */
  public Color getLineColor()
  {
    return lineColor;
  }


  /**
   * Returns the thickness of the line in pixels.
   *
   * @return The line thickness (in pixels).
   */
  public int getThickness()
  {
    return thickness;
  }


  /**
   * Returns whether this LineBorder os drawm with rounded
   * or with plain corners.
   *
   * @return <code>true</code> if the corners are rounded,
   *         <code>false</code> if the corners are plain.
   */
  public boolean getRoundedCorners()
  {
    return roundedCorners;
  }


  /**
   * Determines whether this border fills every pixel in its area
   * when painting.
   *
   * @return <code>true</code> if the corners are plain and the line
   *         color is fully opaque; <code>false</code> if the corners
   *         are rounded or the line color is partially transparent.
   */
  public boolean isBorderOpaque()
  {
    return (!roundedCorners) && (lineColor.getAlpha() == 255);
  }
}