Back to index...

	/*
	* Copyright (c) 1995, 2010, Oracle and/or its affiliates. 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. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/
	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
	}

Back to index...