GTKLookAndFeelFixer.java

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 * Copyright 2015 Arduino LLC (http://www.arduino.cc/)
 */

package processing.app.linux;

import javax.swing.*;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class GTKLookAndFeelFixer {

  /*
   * All functions of this class courtesy of Klaus Reimer
   * https://www.ailis.de/~k/archives/67-Workaround-for-borderless-Java-Swing-menus-on-Linux.html
   */

  /*
   * This is free and unencumbered software released into the public domain.
   *
   * Anyone is free to copy, modify, publish, use, compile, sell, or
   * distribute this software, either in source code form or as a compiled
   * binary, for any purpose, commercial or non-commercial, and by any
   * means.
   *
   * In jurisdictions that recognize copyright laws, the author or authors
   * of this software dedicate any and all copyright interest in the
   * software to the public domain. We make this dedication for the benefit
   * of the public at large and to the detriment of our heirs and
   * successors. We intend this dedication to be an overt act of
   * relinquishment in perpetuity of all present and future rights to this
   * software under copyright law.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
   * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
   * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
   * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
   * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
   * OTHER DEALINGS IN THE SOFTWARE.
   *
   * For more information, please refer to <http://unlicense.org/>
   */

  /**
   * Swing menus are looking pretty bad on Linux when the GTK LaF is used (See
   * bug #6925412). It will most likely never be fixed anytime soon so this
   * method provides a workaround for it. It uses reflection to change the GTK
   * style objects of Swing so popup menu borders have a minimum thickness of
   * 1 and menu separators have a minimum vertical thickness of 1.
   */
  public static void installGtkPopupBugWorkaround() {
    // Get current look-and-feel implementation class
    LookAndFeel laf = UIManager.getLookAndFeel();
    Class<?> lafClass = laf.getClass();

    // Do nothing when not using the problematic LaF
    if (!lafClass.getName().equals("com.sun.java.swing.plaf.gtk.GTKLookAndFeel")) {
      return;
    }

    // We do reflection from here on. Failure is silently ignored. The
    // workaround is simply not installed when something goes wrong here
    try {
      // Access the GTK style factory
      Field field = lafClass.getDeclaredField("styleFactory");
      boolean accessible = field.isAccessible();
      field.setAccessible(true);
      Object styleFactory = field.get(laf);
      field.setAccessible(accessible);

      // Fix the horizontal and vertical thickness of popup menu style
      Object style = getGtkStyle(styleFactory, new JPopupMenu(), "POPUP_MENU");
      fixGtkThickness(style, "yThickness");
      fixGtkThickness(style, "xThickness");

      // Fix the vertical thickness of the popup menu separator style
      style = getGtkStyle(styleFactory, new JSeparator(), "POPUP_MENU_SEPARATOR");
      fixGtkThickness(style, "yThickness");
    } catch (Exception e) {
      // Silently ignored. Workaround can't be applied.
    }
  }

  /**
   * Called internally by installGtkPopupBugWorkaround to fix the thickness
   * of a GTK style field by setting it to a minimum value of 1.
   *
   * @param style     The GTK style object.
   * @param fieldName The field name.
   * @throws Exception When reflection fails.
   */
  private static void fixGtkThickness(Object style, String fieldName) throws Exception {
    Field field = style.getClass().getDeclaredField(fieldName);
    boolean accessible = field.isAccessible();
    field.setAccessible(true);
    field.setInt(style, Math.max(1, field.getInt(style)));
    field.setAccessible(accessible);
  }

  /**
   * Called internally by installGtkPopupBugWorkaround. Returns a specific
   * GTK style object.
   *
   * @param styleFactory The GTK style factory.
   * @param component    The target component of the style.
   * @param regionName   The name of the target region of the style.
   * @return The GTK style.
   * @throws Exception When reflection fails.
   */
  private static Object getGtkStyle(Object styleFactory, JComponent component, String regionName) throws Exception {
    // Create the region object
    Class<?> regionClass = Class.forName("javax.swing.plaf.synth.Region");
    Field field = regionClass.getField(regionName);
    Object region = field.get(regionClass);

    // Get and return the style
    Class<?> styleFactoryClass = styleFactory.getClass();
    Method method = styleFactoryClass.getMethod("getStyle", JComponent.class, regionClass);
    boolean accessible = method.isAccessible();
    method.setAccessible(true);
    Object style = method.invoke(styleFactory, component, region);
    method.setAccessible(accessible);
    return style;
  }
}