/*
 * @(#)Canvas.java	1.35 04/03/16
 *
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
package java.awt;

import java.awt.image.BufferStrategy;
import java.awt.peer.CanvasPeer;
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.
 *
 * @version 	1.35 03/16/04
 * @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();
        graphicsConfig = config;
    }

    /**
     * Construct a name for this component.  Called by getName() when the
     * name is null.
     */
    String constructComponentName() {
        synchronized (getClass()) {
	    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);
    }
    
    /**
     * @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
     */
    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.
     */
    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
}
