/*
* 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
}