/******************************************************************************* * Copyright (c) 2000, 2003 IBM Corporation and others. * All rights reserved. This program and the accompanying materials  * are made available under the terms of the Common Public License v1.0 * which accompanies this distribution, and is available at * http://www.eclipse.org/legal/cpl-v10.html *  * Contributors: *     IBM Corporation - initial API and implementation *******************************************************************************/package org.eclipse.swt.widgets;import org.eclipse.swt.graphics.*;/** * A layout controls the position and size * of the children of a composite widget. * This class is the abstract base class for * layouts.  */public abstract class Layout {/** * Computes and returns the size of the specified * composite's client area according to this layout. * <p> * This method computes the minimum size that the * client area of the composite must be in order to * position all children at their minimum size inside * the composite according to the layout algorithm * encoded by this layout. * </p> * <p> * When a width or height hint is supplied, it is * used to constrain the result. For example, if a * width hint is provided that is less than the minimum * width of the client area, the layout may choose * to wrap and increase height, clip, overlap, or * otherwise constrain the children. * </p> * * @param composite a composite widget using this layout * @param wHint width (<code>SWT.DEFAULT</code> for minimum) * @param hHint height (<code>SWT.DEFAULT</code> for minimum) * @param flushCache <code>true</code> means flush cached layout values * @return a point containing the computed size (width, height) *  * @see #layout * @see Control#getBorderWidth * @see Control#getBounds * @see Control#getSize * @see Control#pack * @see "computeTrim, getClientArea for controls that implement them" */protected abstract Point computeSize (Composite composite, int wHint, int hHint, boolean flushCache);/** * Lays out the children of the specified composite * according to this layout. * <p> * This method positions and sizes the children of a * composite using the layout algorithm encoded by this * layout. Children of the composite are positioned in * the client area of the composite. The position of * the composite is not altered by this method. * </p> * <p> * When the flush cache hint is true, the layout is * instructed to flush any cached values associated * with the children. Typically, a layout will cache * the preferred sizes of the children to avoid the * expense of computing these values each time the * widget is layed out. * </p> * <p> * When layout is triggered explicitly by the programmer * the flush cache hint is true. When layout is triggered * by a resize, either caused by the programmer or by the * user, the hint is false. * </p> * * @param composite a composite widget using this layout * @param flushCache <code>true</code> means flush cached layout values */protected abstract void layout (Composite composite, boolean flushCache);}