1 /*
2 * Copyright (c) 1995, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25 package java.awt;
26
27 import java.awt.image.BufferStrategy;
28 import java.awt.peer.CanvasPeer;
29 import javax.accessibility.*;
30
31 /**
32 * A <code>Canvas</code> component represents a blank rectangular
33 * area of the screen onto which the application can draw or from
34 * which the application can trap input events from the user.
35 * <p>
36 * An application must subclass the <code>Canvas</code> class in
37 * order to get useful functionality such as creating a custom
38 * component. The <code>paint</code> method must be overridden
39 * in order to perform custom graphics on the canvas.
40 *
41 * @author Sami Shaio
42 * @since 1.0
43 */
44 public class Canvas extends Component implements Accessible {
45
46 private static final String base = "canvas";
47 private static int nameCounter = 0;
48
49 /*
50 * JDK 1.1 serialVersionUID
51 */
52 private static final long serialVersionUID = -2284879212465893870L;
53
54 /**
55 * Constructs a new Canvas.
56 */
57 public Canvas() {
58 }
59
60 /**
61 * Constructs a new Canvas given a GraphicsConfiguration object.
62 *
63 * @param config a reference to a GraphicsConfiguration object.
64 *
65 * @see GraphicsConfiguration
66 */
67 public Canvas(GraphicsConfiguration config) {
68 this();
69 setGraphicsConfiguration(config);
70 }
71
72 @Override
73 @SuppressWarnings("deprecation")
74 void setGraphicsConfiguration(GraphicsConfiguration gc) {
75 synchronized(getTreeLock()) {
76 CanvasPeer peer = (CanvasPeer)getPeer();
77 if (peer != null) {
78 gc = peer.getAppropriateGraphicsConfiguration(gc);
79 }
80 super.setGraphicsConfiguration(gc);
81 }
82 }
83
84 /**
85 * Construct a name for this component. Called by getName() when the
86 * name is null.
87 */
88 String constructComponentName() {
89 synchronized (Canvas.class) {
90 return base + nameCounter++;
91 }
92 }
93
94 /**
95 * Creates the peer of the canvas. This peer allows you to change the
96 * user interface of the canvas without changing its functionality.
97 * @see java.awt.Toolkit#createCanvas(java.awt.Canvas)
98 * @see java.awt.Component#getToolkit()
99 */
100 public void addNotify() {
101 synchronized (getTreeLock()) {
102 if (peer == null)
103 peer = getToolkit().createCanvas(this);
104 super.addNotify();
105 }
106 }
107
108 /**
109 * Paints this canvas.
110 * <p>
111 * Most applications that subclass <code>Canvas</code> should
112 * override this method in order to perform some useful operation
113 * (typically, custom painting of the canvas).
114 * The default operation is simply to clear the canvas.
115 * Applications that override this method need not call
116 * super.paint(g).
117 *
118 * @param g the specified Graphics context
119 * @see #update(Graphics)
120 * @see Component#paint(Graphics)
121 */
122 public void paint(Graphics g) {
123 g.clearRect(0, 0, width, height);
124 }
125
126 /**
127 * Updates this canvas.
128 * <p>
129 * This method is called in response to a call to <code>repaint</code>.
130 * The canvas is first cleared by filling it with the background
131 * color, and then completely redrawn by calling this canvas's
132 * <code>paint</code> method.
133 * Note: applications that override this method should either call
134 * super.update(g) or incorporate the functionality described
135 * above into their own code.
136 *
137 * @param g the specified Graphics context
138 * @see #paint(Graphics)
139 * @see Component#update(Graphics)
140 */
141 public void update(Graphics g) {
142 g.clearRect(0, 0, width, height);
143 paint(g);
144 }
145
146 boolean postsOldMouseEvents() {
147 return true;
148 }
149
150 /**
151 * Creates a new strategy for multi-buffering on this component.
152 * Multi-buffering is useful for rendering performance. This method
153 * attempts to create the best strategy available with the number of
154 * buffers supplied. It will always create a <code>BufferStrategy</code>
155 * with that number of buffers.
156 * A page-flipping strategy is attempted first, then a blitting strategy
157 * using accelerated buffers. Finally, an unaccelerated blitting
158 * strategy is used.
159 * <p>
160 * Each time this method is called,
161 * the existing buffer strategy for this component is discarded.
162 * @param numBuffers number of buffers to create, including the front buffer
163 * @exception IllegalArgumentException if numBuffers is less than 1.
164 * @exception IllegalStateException if the component is not displayable
165 * @see #isDisplayable
166 * @see #getBufferStrategy
167 * @since 1.4
168 */
169 public void createBufferStrategy(int numBuffers) {
170 super.createBufferStrategy(numBuffers);
171 }
172
173 /**
174 * Creates a new strategy for multi-buffering on this component with the
175 * required buffer capabilities. This is useful, for example, if only
176 * accelerated memory or page flipping is desired (as specified by the
177 * buffer capabilities).
178 * <p>
179 * Each time this method
180 * is called, the existing buffer strategy for this component is discarded.
181 * @param numBuffers number of buffers to create
182 * @param caps the required capabilities for creating the buffer strategy;
183 * cannot be <code>null</code>
184 * @exception AWTException if the capabilities supplied could not be
185 * supported or met; this may happen, for example, if there is not enough
186 * accelerated memory currently available, or if page flipping is specified
187 * but not possible.
188 * @exception IllegalArgumentException if numBuffers is less than 1, or if
189 * caps is <code>null</code>
190 * @see #getBufferStrategy
191 * @since 1.4
192 */
193 public void createBufferStrategy(int numBuffers,
194 BufferCapabilities caps) throws AWTException {
195 super.createBufferStrategy(numBuffers, caps);
196 }
197
198 /**
199 * Returns the <code>BufferStrategy</code> used by this component. This
200 * method will return null if a <code>BufferStrategy</code> has not yet
201 * been created or has been disposed.
202 *
203 * @return the buffer strategy used by this component
204 * @see #createBufferStrategy
205 * @since 1.4
206 */
207 public BufferStrategy getBufferStrategy() {
208 return super.getBufferStrategy();
209 }
210
211 /*
212 * --- Accessibility Support ---
213 *
214 */
215
216 /**
217 * Gets the AccessibleContext associated with this Canvas.
218 * For canvases, the AccessibleContext takes the form of an
219 * AccessibleAWTCanvas.
220 * A new AccessibleAWTCanvas instance is created if necessary.
221 *
222 * @return an AccessibleAWTCanvas that serves as the
223 * AccessibleContext of this Canvas
224 * @since 1.3
225 */
226 public AccessibleContext getAccessibleContext() {
227 if (accessibleContext == null) {
228 accessibleContext = new AccessibleAWTCanvas();
229 }
230 return accessibleContext;
231 }
232
233 /**
234 * This class implements accessibility support for the
235 * <code>Canvas</code> class. It provides an implementation of the
236 * Java Accessibility API appropriate to canvas user-interface elements.
237 * @since 1.3
238 */
239 protected class AccessibleAWTCanvas extends AccessibleAWTComponent
240 {
241 private static final long serialVersionUID = -6325592262103146699L;
242
243 /**
244 * Get the role of this object.
245 *
246 * @return an instance of AccessibleRole describing the role of the
247 * object
248 * @see AccessibleRole
249 */
250 public AccessibleRole getAccessibleRole() {
251 return AccessibleRole.CANVAS;
252 }
253
254 } // inner class AccessibleAWTCanvas
255 }