/*
 * Copyright (c) 2009, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.swing.plaf;

import javax.accessibility.Accessible;
import javax.swing.*;
import javax.swing.plaf.ComponentUI;
import java.awt.*;
import java.awt.event.*;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeSupport;
import java.beans.PropertyChangeListener;
import java.io.Serializable;

/**
 * The base class for all {@link javax.swing.JLayer}'s UI delegates.
 * <p/>
 * {@link #paint(java.awt.Graphics, javax.swing.JComponent)} method performes the
 * painting of the {@code JLayer}
 * and {@link #eventDispatched(AWTEvent, JLayer)} method is notified
 * about any {@code AWTEvent}s which have been generated by a {@code JLayer}
 * or any of its subcomponents.
 * <p/>
 * The {@code LayerUI} differs from the UI delegates of the other components,
 * because it is LookAndFeel independent and is not updated by default when
 * the system LookAndFeel is changed.
 * <p/>
 * The subclasses of {@code LayerUI} can either be stateless and shareable
 * by multiple {@code JLayer}s or not shareable.
 *
 * @param <V> one of the super types of {@code JLayer}'s view component
 *
 * @see JLayer#setUI(LayerUI)
 * @see JLayer#setView(Component)
 * @see JLayer#getView()
 * @since 1.7
 *
 * @author Alexander Potochkin
 */
public class LayerUI<V extends Component>
        extends ComponentUI implements Serializable {

    private final PropertyChangeSupport propertyChangeSupport =
            new PropertyChangeSupport(this);

    /**
     * Paints the specified component.
     * Subclasses should override this method and use
     * the specified {@code Graphics} object to
     * render the content of the component.
     * <p/>
     * The default implementation paints the passed component as is.
     *
     * @param g the {@code Graphics} context in which to paint
     * @param c the component being painted
     */
    public void paint(Graphics g, JComponent c) {
        c.paint(g);
    }

    /**
     * Processes {@code AWTEvent}s for {@code JLayer}
     * and <b>all its descendants</b> to this {@code LayerUI} instance.
     * <p/>
     * To enable the {@code AWTEvent}s of a particular type,
     * you call {@link JLayer#setLayerEventMask}
     * in {@link #installUI(javax.swing.JComponent)}
     * and set the layer event mask to {@code 0}
     * in {@link #uninstallUI(javax.swing.JComponent)} after that.
     * By default this  method calls the appropriate
     * {@code process&lt;event&nbsp;type&gt;Event}
     * method for the given class of event.
     * <p/>
     * <b>Note:</b> Events are processed only for displayable {@code JLayer}s.
     *
     * @param e the event to be dispatched
     * @param l the layer this LayerUI is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see Component#isDisplayable()
     * @see #processComponentEvent
     * @see #processFocusEvent
     * @see #processKeyEvent
     * @see #processMouseEvent
     * @see #processMouseMotionEvent
     * @see #processInputMethodEvent
     * @see #processHierarchyEvent
     * @see #processMouseWheelEvent
     */
    public void eventDispatched(AWTEvent e, JLayer<? extends V> l){
        if (e instanceof FocusEvent) {
            processFocusEvent((FocusEvent)e, l);

        } else if (e instanceof MouseEvent) {
            switch(e.getID()) {
              case MouseEvent.MOUSE_PRESSED:
              case MouseEvent.MOUSE_RELEASED:
              case MouseEvent.MOUSE_CLICKED:
              case MouseEvent.MOUSE_ENTERED:
              case MouseEvent.MOUSE_EXITED:
                  processMouseEvent((MouseEvent)e, l);
                  break;
              case MouseEvent.MOUSE_MOVED:
              case MouseEvent.MOUSE_DRAGGED:
                  processMouseMotionEvent((MouseEvent)e, l);
                  break;
              case MouseEvent.MOUSE_WHEEL:
                  processMouseWheelEvent((MouseWheelEvent)e, l);
                  break;
            }
        } else if (e instanceof KeyEvent) {
            processKeyEvent((KeyEvent)e, l);
        } else if (e instanceof ComponentEvent) {
            processComponentEvent((ComponentEvent)e, l);
        } else if (e instanceof InputMethodEvent) {
            processInputMethodEvent((InputMethodEvent)e, l);
        } else if (e instanceof HierarchyEvent) {
            switch (e.getID()) {
              case HierarchyEvent.HIERARCHY_CHANGED:
                  processHierarchyEvent((HierarchyEvent)e, l);
                  break;
              case HierarchyEvent.ANCESTOR_MOVED:
              case HierarchyEvent.ANCESTOR_RESIZED:
                  processHierarchyBoundsEvent((HierarchyEvent)e, l);
                  break;
            }
        }
    }

    /**
     * Processes component events occurring on the {@link JLayer}
     * or any of its subcomponents.
     * <p/>
     * This method is not called unless component events are
     * enabled for the {@code JLayer} objects, this {@code LayerUI} is set to.
     * Component events are enabled in the overridden {@link #installUI} method
     * and should be disabled in the {@link #uninstallUI} method after that.
     * <pre>
     * public void installUI(JComponent c) {
     *    super.installUI(c);
     *    JLayer l = (JLayer) c;
     *    l.setLayerEventMask(AWTEvent.COMPONENT_EVENT_MASK);
     * }
     *
     * public void unistallUI(JComponent c) {
     *     super.uninstallUI(c);
     *     JLayer l = (JLayer) c;
     *     l.setLayerEventMask(0);
     * }
     * </pre>
     *
     * @param e the {@code ComponentEvent} to be processed
     * @param l the layer this {@code LayerUI} instance is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see #installUI(javax.swing.JComponent)
     * @see #uninstallUI(javax.swing.JComponent)
     */
    protected void processComponentEvent(ComponentEvent e, JLayer<? extends V> l) {
    }

    /**
     * Processes focus events occurring on the {@link JLayer}
     * or any of its subcomponents.
     * <p/>
     * This method is not called unless focus events are
     * enabled for the {@code JLayer} objects, this {@code LayerUI} is set to.
     * Focus events are enabled in the overridden {@link #installUI} method
     * and should be disabled in the {@link #uninstallUI} method after that.
     * <pre>
     * public void installUI(JComponent c) {
     *    super.installUI(c);
     *    JLayer l = (JLayer) c;
     *    l.setLayerEventMask(AWTEvent.FOCUS_EVENT_MASK);
     * }
     *
     * public void unistallUI(JComponent c) {
     *     super.uninstallUI(c);
     *     JLayer l = (JLayer) c;
     *     l.setLayerEventMask(0);
     * }
     * </pre>
     *
     * @param e the {@code FocusEvent} to be processed
     * @param l the layer this {@code LayerUI} instance is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see #installUI(javax.swing.JComponent)
     * @see #uninstallUI(javax.swing.JComponent)
     */
    protected void processFocusEvent(FocusEvent e, JLayer<? extends V> l) {
    }

    /**
     * Processes key events occurring on the {@link JLayer}
     * or any of its subcomponents.
     * <p/>
     * This method is not called unless key events are
     * enabled for the {@code JLayer} objects, this {@code LayerUI} is set to.
     * Key events are enabled in the overridden {@link #installUI} method
     * and should be disabled in the {@link #uninstallUI} method after that.
     * <pre>
     * public void installUI(JComponent c) {
     *    super.installUI(c);
     *    JLayer l = (JLayer) c;
     *    l.setLayerEventMask(AWTEvent.KEY_EVENT_MASK);
     * }
     *
     * public void unistallUI(JComponent c) {
     *     super.uninstallUI(c);
     *     JLayer l = (JLayer) c;
     *     l.setLayerEventMask(0);
     * }
     * </pre>
     *
     * @param e the {@code KeyEvent} to be processed
     * @param l the layer this {@code LayerUI} instance is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see #installUI(javax.swing.JComponent)
     * @see #uninstallUI(javax.swing.JComponent)
     */
    protected void processKeyEvent(KeyEvent e, JLayer<? extends V> l) {
    }

    /**
     * Processes mouse events occurring on the {@link JLayer}
     * or any of its subcomponents.
     * <p/>
     * This method is not called unless mouse events are
     * enabled for the {@code JLayer} objects, this {@code LayerUI} is set to.
     * Mouse events are enabled in the overridden {@link #installUI} method
     * and should be disabled in the {@link #uninstallUI} method after that.
     * <pre>
     * public void installUI(JComponent c) {
     *    super.installUI(c);
     *    JLayer l = (JLayer) c;
     *    l.setLayerEventMask(AWTEvent.MOUSE_EVENT_MASK);
     * }
     *
     * public void unistallUI(JComponent c) {
     *     super.uninstallUI(c);
     *     JLayer l = (JLayer) c;
     *     l.setLayerEventMask(0);
     * }
     * </pre>
     *
     * @param e the {@code MouseEvent} to be processed
     * @param l the layer this {@code LayerUI} instance is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see #installUI(javax.swing.JComponent)
     * @see #uninstallUI(javax.swing.JComponent)
     */
    protected void processMouseEvent(MouseEvent e, JLayer<? extends V> l) {
    }

    /**
     * Processes mouse motion event occurring on the {@link JLayer}
     * or any of its subcomponents.
     * <p/>
     * This method is not called unless mouse motion events are
     * enabled for the {@code JLayer} objects, this {@code LayerUI} is set to.
     * Mouse motion events are enabled in the overridden {@link #installUI} method
     * and should be disabled in the {@link #uninstallUI} method after that.
     * <pre>
     * public void installUI(JComponent c) {
     *    super.installUI(c);
     *    JLayer l = (JLayer) c;
     *    l.setLayerEventMask(AWTEvent.MOUSE_MOTION_EVENT_MASK);
     * }
     *
     * public void unistallUI(JComponent c) {
     *     super.uninstallUI(c);
     *     JLayer l = (JLayer) c;
     *     l.setLayerEventMask(0);
     * }
     * </pre>
     *
     * @param e the {@code MouseEvent} to be processed
     * @param l the layer this {@code LayerUI} instance is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see #installUI(javax.swing.JComponent)
     * @see #uninstallUI(javax.swing.JComponent)
     */
    protected void processMouseMotionEvent(MouseEvent e, JLayer<? extends V> l) {
    }

    /**
     * Processes mouse wheel event occurring on the {@link JLayer}
     * or any of its subcomponents.
     * <p/>
     * This method is not called unless mouse wheel events are
     * enabled for the {@code JLayer} objects, this {@code LayerUI} is set to.
     * Mouse wheel events are enabled in the overridden {@link #installUI} method
     * and should be disabled in the {@link #uninstallUI} method after that.
     * <pre>
     * public void installUI(JComponent c) {
     *    super.installUI(c);
     *    JLayer l = (JLayer) c;
     *    l.setLayerEventMask(AWTEvent.MOUSE_WHEEL_EVENT_MASK);
     * }
     *
     * public void unistallUI(JComponent c) {
     *     super.uninstallUI(c);
     *     JLayer l = (JLayer) c;
     *     l.setLayerEventMask(0);
     * }
     * </pre>
     *
     * @param e the {@code MouseEvent} to be processed
     * @param l the layer this {@code LayerUI} instance is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see #installUI(javax.swing.JComponent)
     * @see #uninstallUI(javax.swing.JComponent)
     */
    protected void processMouseWheelEvent(MouseWheelEvent e, JLayer<? extends V> l) {
    }

    /**
     * Processes input event occurring on the {@link JLayer}
     * or any of its subcomponents.
     * <p/>
     * This method is not called unless input events are
     * enabled for the {@code JLayer} objects, this {@code LayerUI} is set to.
     * Input events are enabled in the overridden {@link #installUI} method
     * and should be disabled in the {@link #uninstallUI} method after that.
     * <pre>
     * public void installUI(JComponent c) {
     *    super.installUI(c);
     *    JLayer l = (JLayer) c;
     *    l.setLayerEventMask(AWTEvent.INPUT_METHOD_EVENT_MASK);
     * }
     *
     * public void unistallUI(JComponent c) {
     *     super.uninstallUI(c);
     *     JLayer l = (JLayer) c;
     *     l.setLayerEventMask(0);
     * }
     * </pre>
     *
     * @param e the {@code InputMethodEvent} to be processed
     * @param l the layer this {@code LayerUI} instance is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see #installUI(javax.swing.JComponent)
     * @see #uninstallUI(javax.swing.JComponent)
     */
    protected void processInputMethodEvent(InputMethodEvent e, JLayer<? extends V> l) {
    }

    /**
     * Processes hierarchy event occurring on the {@link JLayer}
     * or any of its subcomponents.
     * <p/>
     * This method is not called unless hierarchy events are
     * enabled for the {@code JLayer} objects, this {@code LayerUI} is set to.
     * Hierarchy events are enabled in the overridden {@link #installUI} method
     * and should be disabled in the {@link #uninstallUI} method after that.
     * <pre>
     * public void installUI(JComponent c) {
     *    super.installUI(c);
     *    JLayer l = (JLayer) c;
     *    l.setLayerEventMask(AWTEvent.HIERARCHY_EVENT_MASK);
     * }
     *
     * public void unistallUI(JComponent c) {
     *     super.uninstallUI(c);
     *     JLayer l = (JLayer) c;
     *     l.setLayerEventMask(0);
     * }
     * </pre>
     *
     * @param e the {@code HierarchyEvent} to be processed
     * @param l the layer this {@code LayerUI} instance is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see #installUI(javax.swing.JComponent)
     * @see #uninstallUI(javax.swing.JComponent)
     */
    protected void processHierarchyEvent(HierarchyEvent e, JLayer<? extends V> l) {
    }

    /**
     * Processes hierarchy bounds event occurring on the {@link JLayer}
     * or any of its subcomponents.
     * <p/>
     * This method is not called unless hierarchy bounds events are
     * enabled for the {@code JLayer} objects, this {@code LayerUI} is set to.
     * Hierarchy bounds events are enabled in the overridden {@link #installUI}
     * method and should be disabled in the {@link #uninstallUI} method after that.
     * <pre>
     * public void installUI(JComponent c) {
     *    super.installUI(c);
     *    JLayer l = (JLayer) c;
     *    l.setLayerEventMask(AWTEvent.HIERARCHY_BOUNDS_EVENT_MASK);
     * }
     *
     * public void unistallUI(JComponent c) {
     *     super.uninstallUI(c);
     *     JLayer l = (JLayer) c;
     *     l.setLayerEventMask(0);
     * }
     * </pre>
     *
     * @param e the {@code HierarchyEvent} to be processed
     * @param l the layer this {@code LayerUI} instance is set to
     *
     * @see JLayer#setLayerEventMask(long)
     * @see #installUI(javax.swing.JComponent)
     * @see #uninstallUI(javax.swing.JComponent)
     */
    protected void processHierarchyBoundsEvent(HierarchyEvent e, JLayer<? extends V> l) {
    }

    /**
     * Invoked when {@link javax.swing.JLayer#updateUI()} is called
     * by the {@code JLayer} this {@code LayerUI} is set to.
     *
     * @param l the {@code JLayer} which UI is updated
     */
    public void updateUI(JLayer<? extends V> l){
    }

    /**
     * Configures the {@code JLayer} this {@code LayerUI} is set to.
     * The default implementation registers the {@code LayerUI}
     * as a property change listener for the passed {@code JLayer} component.
     *
     * @param c the {@code JLayer} component where this UI delegate is being installed
     */
    public void installUI(JComponent c) {
        addPropertyChangeListener((JLayer) c);
    }

    /**
     * Reverses the configuration which was previously set
     * in the {@link #installUI(JComponent)} method.
     * The default implementation unregisters the property change listener
     * for the passed JLayer component.
     *
     * @param c the component from which this UI delegate is being removed.
     */
    public void uninstallUI(JComponent c) {
        removePropertyChangeListener((JLayer) c);
    }

    /**
     * Adds a PropertyChangeListener to the listener list. The listener is
     * registered for all bound properties of this class.
     * <p/>
     * If {@code listener} is {@code null},
     * no exception is thrown and no action is performed.
     *
     * @param listener the property change listener to be added
     * @see #removePropertyChangeListener
     * @see #getPropertyChangeListeners
     * @see #addPropertyChangeListener(String, java.beans.PropertyChangeListener)
     */
    public void addPropertyChangeListener(PropertyChangeListener listener) {
        propertyChangeSupport.addPropertyChangeListener(listener);
    }

    /**
     * Removes a PropertyChangeListener from the listener list. This method
     * should be used to remove PropertyChangeListeners that were registered
     * for all bound properties of this class.
     * <p/>
     * If {@code listener} is {@code null},
     * no exception is thrown and no action is performed.
     *
     * @param listener the PropertyChangeListener to be removed
     * @see #addPropertyChangeListener
     * @see #getPropertyChangeListeners
     * @see #removePropertyChangeListener(String, PropertyChangeListener)
     */
    public void removePropertyChangeListener(PropertyChangeListener listener) {
        propertyChangeSupport.removePropertyChangeListener(listener);
    }

    /**
     * Returns an array of all the property change listeners
     * registered on this component.
     *
     * @return all of this ui's {@code PropertyChangeListener}s
     *         or an empty array if no property change
     *         listeners are currently registered
     * @see #addPropertyChangeListener
     * @see #removePropertyChangeListener
     * @see #getPropertyChangeListeners(String)
     */
    public PropertyChangeListener[] getPropertyChangeListeners() {
        return propertyChangeSupport.getPropertyChangeListeners();
    }

    /**
     * Adds a PropertyChangeListener to the listener list for a specific
     * property.
     * <p/>
     * If {@code propertyName} or {@code listener} is {@code null},
     * no exception is thrown and no action is taken.
     *
     * @param propertyName one of the property names listed above
     * @param listener     the property change listener to be added
     * @see #removePropertyChangeListener(String, PropertyChangeListener)
     * @see #getPropertyChangeListeners(String)
     * @see #addPropertyChangeListener(String, PropertyChangeListener)
     */
    public void addPropertyChangeListener(String propertyName,
                                          PropertyChangeListener listener) {
        propertyChangeSupport.addPropertyChangeListener(propertyName, listener);
    }

    /**
     * Removes a {@code PropertyChangeListener} from the listener
     * list for a specific property. This method should be used to remove
     * {@code PropertyChangeListener}s
     * that were registered for a specific bound property.
     * <p/>
     * If {@code propertyName} or {@code listener} is {@code null},
     * no exception is thrown and no action is taken.
     *
     * @param propertyName a valid property name
     * @param listener     the PropertyChangeListener to be removed
     * @see #addPropertyChangeListener(String, PropertyChangeListener)
     * @see #getPropertyChangeListeners(String)
     * @see #removePropertyChangeListener(PropertyChangeListener)
     */
    public void removePropertyChangeListener(String propertyName,
                                             PropertyChangeListener listener) {
        propertyChangeSupport.removePropertyChangeListener(propertyName, listener);
    }

    /**
     * Returns an array of all the listeners which have been associated
     * with the named property.
     *
     * @param propertyName  The name of the property being listened to
     * @return all of the {@code PropertyChangeListener}s associated with
     *         the named property; if no such listeners have been added or
     *         if {@code propertyName} is {@code null}, an empty
     *         array is returned
     * @see #addPropertyChangeListener(String, PropertyChangeListener)
     * @see #removePropertyChangeListener(String, PropertyChangeListener)
     * @see #getPropertyChangeListeners
     */
    public PropertyChangeListener[] getPropertyChangeListeners(String propertyName) {
        return propertyChangeSupport.getPropertyChangeListeners(propertyName);
    }

    /**
     * Support for reporting bound property changes for Object properties.
     * This method can be called when a bound property has changed and it will
     * send the appropriate PropertyChangeEvent to any registered
     * PropertyChangeListeners.
     *
     * @param propertyName the property whose value has changed
     * @param oldValue     the property's previous value
     * @param newValue     the property's new value
     */
    protected void firePropertyChange(String propertyName,
                                      Object oldValue, Object newValue) {
        propertyChangeSupport.firePropertyChange(propertyName, oldValue, newValue);
    }

    /**
     * Notifies the {@code LayerUI} when any of its property are changed
     * and enables updating every {@code JLayer}
     * this {@code LayerUI} instance is set to.
     *
     * @param evt the PropertyChangeEvent generated by this {@code LayerUI}
     * @param l the {@code JLayer} this LayerUI is set to
     */
    public void applyPropertyChange(PropertyChangeEvent evt, JLayer<? extends V> l) {
    }

    /**
     * Returns the preferred size of the viewport for a view component.
     *
     * @param l the {@code JLayer} component where this UI delegate is being installed
     * @return the preferred size of the viewport for a view component
     * @see Scrollable#getPreferredScrollableViewportSize()
     */
    public Dimension getPreferredScrollableViewportSize(JLayer<? extends V> l) {
        if (l.getView() instanceof Scrollable) {
            return ((Scrollable)l.getView()).getPreferredScrollableViewportSize();
        }
        return l.getPreferredSize();
    }

    /**
     * Returns a scroll increment, which is required for components
     * that display logical rows or columns in order to completely expose
     * one block of rows or columns, depending on the value of orientation.
     *
     * @param l the {@code JLayer} component where this UI delegate is being installed
     * @param visibleRect The view area visible within the viewport
     * @param orientation Either SwingConstants.VERTICAL or SwingConstants.HORIZONTAL.
     * @param direction Less than zero to scroll up/left, greater than zero for down/right.
     * @return the "block" increment for scrolling in the specified direction
     * @see Scrollable#getScrollableBlockIncrement(Rectangle, int, int)
     */
     public int getScrollableBlockIncrement(JLayer<? extends V> l,
                                           Rectangle visibleRect,
                                           int orientation, int direction) {
        if (l.getView() instanceof Scrollable) {
            return ((Scrollable)l.getView()).getScrollableBlockIncrement(
                    visibleRect,orientation, direction);
        }
        return (orientation == SwingConstants.VERTICAL) ? visibleRect.height :
            visibleRect.width;
    }

    /**
     * Returns {@code false} to indicate that the height of the viewport does not
     * determine the height of the layer, unless the preferred height
     * of the layer is smaller than the height of the viewport.
     *
     * @param l the {@code JLayer} component where this UI delegate is being installed
     * @return whether the layer should track the height of the viewport
     * @see Scrollable#getScrollableTracksViewportHeight()
     */
    public boolean getScrollableTracksViewportHeight(JLayer<? extends V> l) {
        if (l.getView() instanceof Scrollable) {
            return ((Scrollable)l.getView()).getScrollableTracksViewportHeight();
        }
        return false;
    }

    /**
     * Returns {@code false} to indicate that the width of the viewport does not
     * determine the width of the layer, unless the preferred width
     * of the layer is smaller than the width of the viewport.
     *
     * @param l the {@code JLayer} component where this UI delegate is being installed
     * @return whether the layer should track the width of the viewport
     * @see Scrollable
     * @see LayerUI#getScrollableTracksViewportWidth(JLayer)
     */
    public boolean getScrollableTracksViewportWidth(JLayer<? extends V> l) {
        if (l.getView() instanceof Scrollable) {
            return ((Scrollable)l.getView()).getScrollableTracksViewportWidth();
        }
        return false;
    }

    /**
     * Returns a scroll increment, which is required for components
     * that display logical rows or columns in order to completely expose
     * one new row or column, depending on the value of orientation.
     * Ideally, components should handle a partially exposed row or column
     * by returning the distance required to completely expose the item.
     * <p>
     * Scrolling containers, like JScrollPane, will use this method
     * each time the user requests a unit scroll.
     *
     * @param l the {@code JLayer} component where this UI delegate is being installed
     * @param visibleRect The view area visible within the viewport
     * @param orientation Either SwingConstants.VERTICAL or SwingConstants.HORIZONTAL.
     * @param direction Less than zero to scroll up/left, greater than zero for down/right.
     * @return The "unit" increment for scrolling in the specified direction.
     *         This value should always be positive.
     * @see Scrollable#getScrollableUnitIncrement(Rectangle, int, int)
     */
    public int getScrollableUnitIncrement(JLayer<? extends V> l,
                                          Rectangle visibleRect,
                                          int orientation, int direction) {
        if (l.getView() instanceof Scrollable) {
            return ((Scrollable)l.getView()).getScrollableUnitIncrement(
                    visibleRect, orientation, direction);
        }
        return 1;
    }

    /**
     * If the {@code JLayer}'s view component is not {@code null},
     * this calls the view's {@code getBaseline()} method.
     * Otherwise, the default implementation is called.
     *
     * @param c {@code JLayer} to return baseline resize behavior for
     * @param width the width to get the baseline for
     * @param height the height to get the baseline for
     * @return baseline or a value &lt; 0 indicating there is no reasonable
     *                  baseline
     */
    public int getBaseline(JComponent c, int width, int height) {
        JLayer l = (JLayer) c;
        if (l.getView() != null) {
            return l.getView().getBaseline(width, height);
        }
        return super.getBaseline(c, width, height);
     }

    /**
     * If the {@code JLayer}'s view component is not {@code null},
     * this calls the view's {@code getBaselineResizeBehavior()} method.
     * Otherwise, the default implementation is called.
     *
     * @param c {@code JLayer} to return baseline resize behavior for
     * @return an enum indicating how the baseline changes as the component
     *         size changes
     */
    public Component.BaselineResizeBehavior getBaselineResizeBehavior(JComponent c) {
        JLayer l = (JLayer) c;
        if (l.getView() != null) {
            return l.getView().getBaselineResizeBehavior();
        }
        return super.getBaselineResizeBehavior(c);
    }
}