/*
 * Copyright (c) 1995, 2010, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */
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.
 *
 * @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();
 setGraphicsConfiguration(config);
 }

 @Override
 void setGraphicsConfiguration(GraphicsConfiguration gc) {
 synchronized(getTreeLock()) {
 CanvasPeer peer = (CanvasPeer)getPeer();
 if (peer != null) {
 gc = peer.getAppropriateGraphicsConfiguration(gc);
 }
 super.setGraphicsConfiguration(gc);
 }
 }

 /**
 * 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
}