/*

 * Copyright 1995-2007 Sun Microsystems, Inc.  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.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.awt;

import java.awt.image.BufferStrategy;

import javax.accessibility.*;

/**

 * A <code>Canvas</code> component represents a blank rectangular

 * area of the screen onto which the application can draw or from

 * which the application can trap input events from the user.

 * <p>

 * An application must subclass the <code>Canvas</code> class in

 * order to get useful functionality such as creating a custom

 * component. The <code>paint</code> method must be overridden

 * in order to perform custom graphics on the canvas.

 *

 * @author      Sami Shaio

 * @since       JDK1.0

 */

public class Canvas extends Component implements Accessible {

    private static final String base = "canvas";

    private static int nameCounter = 0;

    /*

     * JDK 1.1 serialVersionUID

     */

     private static final long serialVersionUID = -2284879212465893870L;

    /**

     * Constructs a new Canvas.

     */

    public Canvas() {

    }

    /**

     * Constructs a new Canvas given a GraphicsConfiguration object.

     *

     * @param config a reference to a GraphicsConfiguration object.

     *

     * @see GraphicsConfiguration

     */

    public Canvas(GraphicsConfiguration config) {

        this();

    }

    /**

     * Construct a name for this component.  Called by getName() when the

     * name is null.

     */

    String constructComponentName() {

        synchronized (Canvas.class) {

            return base + nameCounter++;

        }

    }

    /**

     * Creates the peer of the canvas.  This peer allows you to change the

     * user interface of the canvas without changing its functionality.

     * @see     java.awt.Toolkit#createCanvas(java.awt.Canvas)

     * @see     java.awt.Component#getToolkit()

     */

    public void addNotify() {

        synchronized (getTreeLock()) {

            if (peer == null)

                peer = getToolkit().createCanvas(this);

            super.addNotify();

        }

    }

    /**

     * Paints this canvas.

     * <p>

     * Most applications that subclass <code>Canvas</code> should

     * override this method in order to perform some useful operation

     * (typically, custom painting of the canvas).

     * The default operation is simply to clear the canvas.

     * Applications that override this method need not call

     * super.paint(g).

     *

     * @param      g   the specified Graphics context

     * @see        #update(Graphics)

     * @see        Component#paint(Graphics)

     */

    public void paint(Graphics g) {

        g.clearRect(0, 0, width, height);

    }

    /**

     * Updates this canvas.

     * <p>

     * This method is called in response to a call to <code>repaint</code>.

     * The canvas is first cleared by filling it with the background

     * color, and then completely redrawn by calling this canvas's

     * <code>paint</code> method.

     * Note: applications that override this method should either call

     * super.update(g) or incorporate the functionality described

     * above into their own code.

     *

     * @param g the specified Graphics context

     * @see   #paint(Graphics)

     * @see   Component#update(Graphics)

     */

    public void update(Graphics g) {

        g.clearRect(0, 0, width, height);

        paint(g);

    }

    boolean postsOldMouseEvents() {

        return true;

    }

    /**

     * Creates a new strategy for multi-buffering on this component.

     * Multi-buffering is useful for rendering performance.  This method

     * attempts to create the best strategy available with the number of

     * buffers supplied.  It will always create a <code>BufferStrategy</code>

     * with that number of buffers.

     * A page-flipping strategy is attempted first, then a blitting strategy

     * using accelerated buffers.  Finally, an unaccelerated blitting

     * strategy is used.

     * <p>

     * Each time this method is called,

     * the existing buffer strategy for this component is discarded.

     * @param numBuffers number of buffers to create, including the front buffer

     * @exception IllegalArgumentException if numBuffers is less than 1.

     * @exception IllegalStateException if the component is not displayable

     * @see #isDisplayable

     * @see #getBufferStrategy

     * @since 1.4

     */

    public void createBufferStrategy(int numBuffers) {

        super.createBufferStrategy(numBuffers);

    }

    /**

     * Creates a new strategy for multi-buffering on this component with the

     * required buffer capabilities.  This is useful, for example, if only

     * accelerated memory or page flipping is desired (as specified by the

     * buffer capabilities).

     * <p>

     * Each time this method

     * is called, the existing buffer strategy for this component is discarded.

     * @param numBuffers number of buffers to create

     * @param caps the required capabilities for creating the buffer strategy;

     * cannot be <code>null</code>

     * @exception AWTException if the capabilities supplied could not be

     * supported or met; this may happen, for example, if there is not enough

     * accelerated memory currently available, or if page flipping is specified

     * but not possible.

     * @exception IllegalArgumentException if numBuffers is less than 1, or if

     * caps is <code>null</code>

     * @see #getBufferStrategy

     * @since 1.4

     */

    public void createBufferStrategy(int numBuffers,

        BufferCapabilities caps) throws AWTException {

        super.createBufferStrategy(numBuffers, caps);

    }

    /**

     * Returns the <code>BufferStrategy</code> used by this component.  This

     * method will return null if a <code>BufferStrategy</code> has not yet

     * been created or has been disposed.

     *

     * @return the buffer strategy used by this component

     * @see #createBufferStrategy

     * @since 1.4

     */

    public BufferStrategy getBufferStrategy() {

        return super.getBufferStrategy();

    }

    /*

     * --- Accessibility Support ---

     *

     */

    /**

     * Gets the AccessibleContext associated with this Canvas.

     * For canvases, the AccessibleContext takes the form of an

     * AccessibleAWTCanvas.

     * A new AccessibleAWTCanvas instance is created if necessary.

     *

     * @return an AccessibleAWTCanvas that serves as the

     *         AccessibleContext of this Canvas

     * @since 1.3

     */

    public AccessibleContext getAccessibleContext() {

        if (accessibleContext == null) {

            accessibleContext = new AccessibleAWTCanvas();

        }

        return accessibleContext;

    }

    /**

     * This class implements accessibility support for the

     * <code>Canvas</code> class.  It provides an implementation of the

     * Java Accessibility API appropriate to canvas user-interface elements.

     * @since 1.3

     */

    protected class AccessibleAWTCanvas extends AccessibleAWTComponent

    {

        private static final long serialVersionUID = -6325592262103146699L;

        /**

         * Get the role of this object.

         *

         * @return an instance of AccessibleRole describing the role of the

         * object

         * @see AccessibleRole

         */

        public AccessibleRole getAccessibleRole() {

            return AccessibleRole.CANVAS;

        }

    } // inner class AccessibleAWTCanvas

}