package org.eclipse.swt.widgets;

/*
 * (c) Copyright IBM Corp. 2000, 2001.
 * All Rights Reserved
 */
 
import org.eclipse.swt.internal.motif.*;
import org.eclipse.swt.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.events.*;

/**
 * Instances of this class are selectable user interface
 * objects that represent a range of positive, numeric values. 
 * <p>
 * At any given moment, a given scroll bar will have a 
 * single <em>selection</em> that is considered to be its
 * value, which is constrained to be within the range of
 * values the scroll bar represents (that is, between its
 * <em>minimum</em> and <em>maximum</em> values).
 * </p><p>
 * Typically, scroll bars will be made up of five areas:
 * <ol>
 * <li>an arrow button for decrementing the value</li>
 * <li>a page decrement area for decrementing the value by a larger amount</li>
 * <li>a <em>thumb</em> for modifying the value by mouse dragging</li>
 * <li>a page increment area for incrementing the value by a larger amount</li>
 * <li>an arrow button for incrementing the value</li>
 * </ol>
 * Based on their style, scroll bars are either <code>HORIZONTAL</code>
 * (which have left and right facing buttons for incrementing and
 * decrementing the value) or <code>VERTICAL</code> (which have
 * up and down facing buttons for incrementing and decrementing
 * the value).
 * </p><p>
 * On some platforms, the size of the scroll bar's thumb can be
 * varied relative to the magnitude of the range of values it
 * represents (that is, relative to the difference between its
 * maximum and minimum values). Typically, this is used to
 * indicate some proportional value such as the ratio of the
 * visible area of a document to the total amount of space that
 * it would take to display it. SWT supports setting the thumb
 * size even if the underlying platform does not, but in this
 * case the appearance of the scroll bar will not change.
 * </p><p>
 * Scroll bars are created by specifying either <code>H_SCROLL</code>,
 * <code>V_SCROLL</code> or both when creating a <code>Scrollable</code>.
 * They are accessed from the <code>Scrollable</code> using
 * <code>getHorizontalBar</code> and <code>getVerticalBar</code>.
 * </p><p>
 * Note: Scroll bars are not Controls.  On some platforms, scroll bars
 * that appear as part of some standard controls such as a text or list
 * have no operating system resources and are not children of the control.
 * For this reason, scroll bars are treated specially.  To create a control
 * that looks like a scroll bar but has operating system resources, use
 * <code>Slider</code>. 
 * </p>
 * <dl>
 * <dt><b>Styles:</b></dt>
 * <dd>HORIZONTAL, VERTICAL</dd>
 * <dt><b>Events:</b></dt>
 * <dd>Selection</dd>
 * </dl>
 * <p>
 * IMPORTANT: This class is <em>not</em> intended to be subclassed.
 *
 * @see Slider
 * @see Scrollable
 * @see Scrollable#getHorizontalBar
 * @see Scrollable#getVerticalBar
 */

public /*final*/ class ScrollBar extends Widget {
	Scrollable parent;
ScrollBar () {
	/* Do Nothing */
}
ScrollBar (Scrollable parent, int style) {
	super (parent, checkStyle (style));
	this.parent = parent;
	createWidget (0);
}
/**
 * Adds the listener to the collection of listeners who will
 * be notified when the receiver's value changes, by sending
 * it one of the messages defined in the <code>SelectionListener</code>
 * interface.
 * <p>
 * When <code>widgetSelected</code> is called, the event object detail field contains one of the following values:
 * <code>0</code> - for the end of a drag.
 * <code>SWT.DRAG</code>.
 * <code>SWT.HOME</code>.
 * <code>SWT.END</code>.
 * <code>SWT.ARROW_DOWN</code>.
 * <code>SWT.ARROW_UP</code>.
 * <code>SWT.PAGE_DOWN</code>.
 * <code>SWT.PAGE_UP</code>.
 * <code>widgetDefaultSelected</code> is not called.
 * </p>
 *
 * @param listener the listener which should be notified
 *
 * @exception IllegalArgumentException <ul>
 *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
 * </ul>
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see SelectionListener
 * @see #removeSelectionListener
 * @see SelectionEvent
 */
public void addSelectionListener(SelectionListener listener) {
	checkWidget();
	if (listener == null) error (SWT.ERROR_NULL_ARGUMENT);
	TypedListener typedListener = new TypedListener(listener);
	addListener(SWT.Selection,typedListener);
	addListener(SWT.DefaultSelection,typedListener);
}
static int checkStyle (int style) {
	return checkBits (style, SWT.HORIZONTAL, SWT.VERTICAL, 0, 0, 0, 0);
}
void createHandle (int index) {
	state |= HANDLE;
	int [] argList = {
		OS.XmNancestorSensitive, 1,
		OS.XmNborderWidth, (style & SWT.BORDER) != 0 ? 1 : 0,
		OS.XmNorientation, ((style & SWT.H_SCROLL) != 0) ? OS.XmHORIZONTAL : OS.XmVERTICAL,
	};
	int parentHandle = parent.scrolledHandle;
	handle = OS.XmCreateScrollBar (parentHandle, null, argList, argList.length / 2);
	if (handle == 0) error (SWT.ERROR_NO_HANDLES);
}
/**
* Gets the Display.
*/
public Display getDisplay () {
	Scrollable parent = this.parent;
	if (parent == null) error (SWT.ERROR_WIDGET_DISPOSED);
	return parent.getDisplay ();
}
/**
 * Returns <code>true</code> if the receiver is enabled, and
 * <code>false</code> otherwise. A disabled control is typically
 * not selectable from the user interface and draws with an
 * inactive or "grayed" look.
 *
 * @return the enabled state
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public boolean getEnabled () {
	checkWidget();
	int [] argList = {OS.XmNsensitive, 0};
	OS.XtGetValues (handle, argList, argList.length / 2);
	return argList [1] != 0;
}
/**
 * Returns the amount that the receiver's value will be
 * modified by when the up/down (or right/left) arrows
 * are pressed.
 *
 * @return the increment
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public int getIncrement () {
	checkWidget();
	int [] argList = {OS.XmNincrement, 0};
	OS.XtGetValues (handle, argList, argList.length / 2);
	return argList [1];
}
/**
 * Returns the maximum value which the receiver will allow.
 *
 * @return the maximum
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public int getMaximum () {
	checkWidget();
	int [] argList = {OS.XmNmaximum, 0};
	OS.XtGetValues (handle, argList, argList.length / 2);
	return argList [1];
}
/**
 * Returns the minimum value which the receiver will allow.
 *
 * @return the minimum
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public int getMinimum () {
	checkWidget();
	int [] argList = {OS.XmNminimum, 0};
	OS.XtGetValues (handle, argList, argList.length / 2);
	return argList [1];
}
/**
 * Returns the amount that the receiver's value will be
 * modified by when the page increment/decrement areas
 * are selected.
 *
 * @return the page increment
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public int getPageIncrement () {
	checkWidget();
	int [] argList = {OS.XmNpageIncrement, 0};
	OS.XtGetValues (handle, argList, argList.length / 2);
	return argList [1];
}
/**
 * Returns the receiver's parent, which must be scrollable.
 *
 * @return the receiver's parent
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public Scrollable getParent () {
	checkWidget();
	return parent;
}
/**
 * Returns the single <em>selection</em> that is the receiver's value.
 *
 * @return the selection
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public int getSelection () {
	checkWidget();
	int [] argList = {OS.XmNvalue, 0};
	OS.XtGetValues (handle, argList, argList.length / 2);
	return argList [1];
}
/**
 * For horizontal scroll bars, returns the height of the 
 * instance, and for vertical scroll bars, returns the width
 * of the instance.
 *
 * @return the scroll bar size
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public Point getSize () {
	checkWidget();
	int [] argList = {OS.XmNwidth, 0, OS.XmNheight, 0, OS.XmNborderWidth, 0};
	OS.XtGetValues (handle, argList, argList.length / 2);
	int borders = argList [5] * 2;
	return new Point (argList [1] + borders, argList [3] + borders);
}
/**
 * Answers the size of the receiver's thumb relative to the
 * difference between its maximum and minimum values.
 *
 * @return the thumb value
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see ScrollBar
 */
public int getThumb () {
	checkWidget();
	int [] argList = {OS.XmNsliderSize, 0};
	OS.XtGetValues (handle, argList, argList.length / 2);
	return argList [1];
}
/**
 * Returns <code>true</code> if the receiver is visible, and
 * <code>false</code> otherwise.
 * <p>
 * If one of the receiver's ancestors is not visible or some
 * other condition makes the receiver not visible, this method
 * may still indicate that it is considered visible even though
 * it may not actually be showing.
 * </p>
 *
 * @return the receiver's visibility state
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public boolean getVisible () {
	checkWidget();
	return OS.XtIsManaged (handle);
}
void hookEvents () {
	int windowProc = parent.getDisplay ().windowProc;
	OS.XtAddCallback (handle, OS.XmNvalueChangedCallback, windowProc, SWT.Selection);
	OS.XtAddCallback (handle, OS.XmNdragCallback, windowProc, SWT.Selection);
	OS.XtAddCallback (handle, OS.XmNtoBottomCallback, windowProc, SWT.Selection);
	OS.XtAddCallback (handle, OS.XmNincrementCallback, windowProc, SWT.Selection);
	OS.XtAddCallback (handle, OS.XmNdecrementCallback, windowProc, SWT.Selection);
	OS.XtAddCallback (handle, OS.XmNpageIncrementCallback, windowProc, SWT.Selection);
	OS.XtAddCallback (handle, OS.XmNpageDecrementCallback, windowProc, SWT.Selection);
	OS.XtAddCallback (handle, OS.XmNtoTopCallback, windowProc, SWT.Selection);
}
/**
 * Returns <code>true</code> if the receiver is enabled, and
 * <code>false</code> otherwise. A disabled control is typically
 * not selectable from the user interface and draws with an
 * inactive or "grayed" look.
 * <p>
 * Note: Because of the strong connection between a scroll bar
 * and the widget which contains it (its parent), a scroll bar
 * will not indicate that it is enabled if its parent is not.
 * </p>
 *
 * @return the receiver's enabled state
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public boolean isEnabled () {
	checkWidget();
	return getEnabled () && parent.isEnabled ();
}
/**
 * Returns <code>true</code> if the receiver is visible, and
 * <code>false</code> otherwise.
 * <p>
 * If one of the receiver's ancestors is not visible or some
 * other condition makes the receiver not visible, this method
 * may still indicate that it is considered visible even though
 * it may not actually be showing.
 * </p>
 *
 * @return the receiver's visibility state
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public boolean isVisible () {
	checkWidget();
	return getVisible () && parent.isVisible ();
}
void manageChildren () {
	OS.XtManageChild (handle);
}
int processSelection (int callData) {
	XmAnyCallbackStruct struct = new XmAnyCallbackStruct ();
	OS.memmove (struct, callData, XmAnyCallbackStruct.sizeof);
	Event event = new Event ();
	switch (struct.reason) {
		case OS.XmCR_DRAG:		event.detail = SWT.DRAG;  break;
		/*
		* Do not set the detail field to SWT.DRAG 
		* to indicate that the dragging has ended.
		*/
//		case OS.XmCR_VALUE_CHANGED:	break; 
		case OS.XmCR_TO_TOP:		event.detail = SWT.HOME;  break;
		case OS.XmCR_TO_BOTTOM:		event.detail = SWT.END;  break;
		case OS.XmCR_DECREMENT:		event.detail = SWT.ARROW_UP;  break;
		case OS.XmCR_INCREMENT:		event.detail = SWT.ARROW_DOWN;  break;
		case OS.XmCR_PAGE_DECREMENT: 	event.detail = SWT.PAGE_UP;  break;
		case OS.XmCR_PAGE_INCREMENT: 	event.detail = SWT.PAGE_DOWN;  break;
	}
	
	/*
	* Feature in Motif.  When a scroll bar is selected,
	* it does not make the shell active.  The fix is to
	* make the shell active.
	*/
	Shell shell = parent.getShell ();
	shell.bringToTop ();
	
	sendEvent (SWT.Selection, event);
	return 0;
}
void releaseChild () {
	super.releaseChild ();
	if (parent.horizontalBar == this) parent.horizontalBar = null;
	if (parent.verticalBar == this) parent.verticalBar = null;
}
void releaseWidget () {
	super.releaseWidget ();
	parent = null;
}
/**
 * Removes the listener from the collection of listeners who will
 * be notified when the receiver's value changes.
 *
 * @param listener the listener which should no longer be notified
 *
 * @exception IllegalArgumentException <ul>
 *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
 * </ul>
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see SelectionListener
 * @see #addSelectionListener
 */
public void removeSelectionListener(SelectionListener listener) {
	checkWidget();
	if (listener == null) error (SWT.ERROR_NULL_ARGUMENT);
	if (eventTable == null) return;
	eventTable.unhook(SWT.Selection, listener);
	eventTable.unhook(SWT.DefaultSelection,listener);	
}
/**
 * Enables the receiver if the argument is <code>true</code>,
 * and disables it otherwise. A disabled control is typically
 * not selectable from the user interface and draws with an
 * inactive or "grayed" look.
 *
 * @param enabled the new enabled state
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public void setEnabled (boolean enabled) {
	checkWidget();
	int [] argList = {OS.XmNsensitive, enabled ? 1 : 0};
	OS.XtSetValues (handle, argList, argList.length / 2);
}
/**
 * Sets the amount that the receiver's value will be
 * modified by when the up/down (or right/left) arrows
 * are pressed to the argument, which must be at least 
 * one.
 *
 * @param value the new increment (must be greater than zero)
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public void setIncrement (int value) {
	checkWidget();
	if (value < 1) return;
	int [] argList = {OS.XmNincrement, value};
	OS.XtSetValues (handle, argList, argList.length / 2);
}
/**
 * Sets the maximum value which the receiver will allow
 * to be the argument which must be greater than or
 * equal to zero.
 *
 * @param value the new maximum (must be zero or greater)
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public void setMaximum (int value) {
	checkWidget();
	if (value < 0) return;
	int [] argList = {OS.XmNmaximum, value};
	Display display = getDisplay ();
	boolean warnings = display.getWarnings ();
	display.setWarnings (false);
	OS.XtSetValues (handle, argList, argList.length / 2);
	display.setWarnings (warnings);
}
/**
 * Sets the minimum value which the receiver will allow
 * to be the argument which must be greater than or
 * equal to zero.
 *
 * @param value the new minimum (must be zero or greater)
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public void setMinimum (int value) {
	checkWidget();
	if (value < 0) return;
	int [] argList = {
		OS.XmNminimum, 0,
		OS.XmNmaximum, 0,
		OS.XmNsliderSize, 0,
	};
	/*
	* Feature in Motif.  For some reason, when minimium
	* is set to be greater than or equal to maximum, Motif
	* does not set the minimum.  Instead, the value is
	* changed and the minimum stays the same.  This behavior
	* differs from setting the maximum where the slider size
	* is always decreased to make room for the new maximum.
	* The fix is to decrease the slider to make room for
	* the new minimum.
	*/
	OS.XtGetValues (handle, argList, argList.length / 2);
	if (argList [3] - value - argList [5] < 0) {
		argList [5] = argList [3] - value;
	}
	argList [1] = value;
	Display display = getDisplay ();
	boolean warnings = display.getWarnings ();
	display.setWarnings (false);
	OS.XtSetValues (handle, argList, argList.length / 2);
	display.setWarnings (warnings);
}
/**
 * Sets the amount that the receiver's value will be
 * modified by when the page increment/decrement areas
 * are selected to the argument, which must be at least
 * one.
 *
 * @return the page increment (must be greater than zero)
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public void setPageIncrement (int value) {
	checkWidget();
	if (value < 1) return;
	int [] argList = {OS.XmNpageIncrement, value};
	OS.XtSetValues (handle, argList, argList.length / 2);
}
/**
 * Sets the single <em>selection</em> that is the receiver's
 * value to the argument which must be greater than or equal
 * to zero.
 *
 * @param value the new selection (must be zero or greater)
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public void setSelection (int selection) {
	checkWidget();
	if (selection < 0) return;
	int [] argList = {OS.XmNvalue, selection};
	Display display = getDisplay ();
	boolean warnings = display.getWarnings ();
	display.setWarnings (false);
	OS.XtSetValues (handle, argList, argList.length / 2);
	display.setWarnings (warnings);
}
/**
 * Sets the size of the receiver's thumb relative to the
 * difference between its maximum and minimum values to the
 * argument which must be at least one.
 *
 * @param value the new thumb value (must be at least one)
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see ScrollBar
 */
public void setThumb (int value) {
	checkWidget();
	if (value < 1) return;
	int [] argList = {OS.XmNsliderSize, value};
	Display display = getDisplay ();
	boolean warnings = display.getWarnings ();
	display.setWarnings (false);
	OS.XtSetValues (handle, argList, argList.length / 2);
	display.setWarnings (warnings);
}
/**
 * Sets the receiver's selection, minimum value, maximum
 * value, thumb, increment and page increment all at once.
 * <p>
 * Note: This is equivalent to setting the values individually
 * using the appropriate methods, but may be implemented in a 
 * more efficient fashion on some platforms.
 * </p>
 *
 * @param selection the new selection value
 * @param minimum the new minimum value
 * @param maximum the new maximum value
 * @param thumb the new thumb value
 * @param increment the new increment value
 * @param pageIncrement the new pageIncrement value
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public void setValues (int selection, int minimum, int maximum, int thumb, int increment, int pageIncrement) {
	checkWidget();
	if (selection < 0) return;
	if (minimum < 0) return;
	if (maximum < 0) return;
	if (thumb < 1) return;
	if (maximum - minimum - thumb < 0) return;
	if (increment < 1) return;
	if (pageIncrement < 1) return;
	int [] argList = {
		OS.XmNvalue, selection,
		OS.XmNminimum, minimum,
		OS.XmNmaximum, maximum,
		OS.XmNsliderSize, thumb,
		OS.XmNincrement, increment,
		OS.XmNpageIncrement, pageIncrement,
	};
	Display display = getDisplay ();
	boolean warnings = display.getWarnings ();
	display.setWarnings (false);
	OS.XtSetValues (handle, argList, argList.length / 2);
	display.setWarnings (warnings);
}
/**
 * Marks the receiver as visible if the argument is <code>true</code>,
 * and marks it invisible otherwise. 
 * <p>
 * If one of the receiver's ancestors is not visible or some
 * other condition makes the receiver not visible, marking
 * it visible may not actually cause it to be displayed.
 * </p>
 *
 * @param visible the new visibility state
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public void setVisible (boolean visible) {
	checkWidget();
	/*
	* Feature in Motif.  Hiding or showing a scroll bar
	* can cause the widget to automatically resize in
	* the OS.  This behavior is unwanted.  The fix is
	* to force the widget to resize to original size.
	*/
	int scrolledHandle = parent.scrolledHandle;
	int [] argList = {OS.XmNwidth, 0, OS.XmNheight, 0};
	OS.XtGetValues (scrolledHandle, argList, argList.length / 2);

	/* Hide or show the scroll bar */
	if (visible) {
		OS.XtManageChild (handle);
	} else {
		OS.XtUnmanageChild (handle);
	}

	/* Restore the size */
	OS.XtSetValues (scrolledHandle, argList, argList.length / 2);
}
}