1 /*
2 * Copyright (c) 1995, 2015, 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 void setGraphicsConfiguration(GraphicsConfiguration gc) {
74 synchronized(getTreeLock()) {
75 CanvasPeer peer = (CanvasPeer) this.peer;
76 if (peer != null) {
77 gc = peer.getAppropriateGraphicsConfiguration(gc);
78 }
79 super.setGraphicsConfiguration(gc);
80 }
81 }
82
83 /**
84 * Construct a name for this component. Called by getName() when the
85 * name is null.
86 */
87 String constructComponentName() {
88 synchronized (Canvas.class) {
89 return base + nameCounter++;
90 }
91 }
92
93 /**
94 * Creates the peer of the canvas. This peer allows you to change the
95 * user interface of the canvas without changing its functionality.
96 * @see java.awt.Component#getToolkit()
97 */
98 public void addNotify() {
99 synchronized (getTreeLock()) {
100 if (peer == null)
101 peer = getComponentFactory().createCanvas(this);
102 super.addNotify();
103 }
104 }
105
106 /**
107 * Paints this canvas.
108 * <p>
109 * Most applications that subclass <code>Canvas</code> should
110 * override this method in order to perform some useful operation
111 * (typically, custom painting of the canvas).
112 * The default operation is simply to clear the canvas.
113 * Applications that override this method need not call
114 * super.paint(g).
115 *
116 * @param g the specified Graphics context
117 * @see #update(Graphics)
118 * @see Component#paint(Graphics)
119 */
120 public void paint(Graphics g) {
121 g.clearRect(0, 0, width, height);
122 }
123
124 /**
125 * Updates this canvas.
126 * <p>
127 * This method is called in response to a call to <code>repaint</code>.
128 * The canvas is first cleared by filling it with the background
129 * color, and then completely redrawn by calling this canvas's
130 * <code>paint</code> method.
131 * Note: applications that override this method should either call
132 * super.update(g) or incorporate the functionality described
133 * above into their own code.
134 *
135 * @param g the specified Graphics context
136 * @see #paint(Graphics)
137 * @see Component#update(Graphics)
138 */
139 public void update(Graphics g) {
140 g.clearRect(0, 0, width, height);
141 paint(g);
142 }
143
144 boolean postsOldMouseEvents() {
145 return true;
146 }
147
148 /**
149 * Creates a new strategy for multi-buffering on this component.
150 * Multi-buffering is useful for rendering performance. This method
151 * attempts to create the best strategy available with the number of
152 * buffers supplied. It will always create a <code>BufferStrategy</code>
153 * with that number of buffers.
154 * A page-flipping strategy is attempted first, then a blitting strategy
155 * using accelerated buffers. Finally, an unaccelerated blitting
156 * strategy is used.
157 * <p>
158 * Each time this method is called,
159 * the existing buffer strategy for this component is discarded.
160 * @param numBuffers number of buffers to create, including the front buffer
161 * @exception IllegalArgumentException if numBuffers is less than 1.
162 * @exception IllegalStateException if the component is not displayable
163 * @see #isDisplayable
164 * @see #getBufferStrategy
165 * @since 1.4
166 */
167 public void createBufferStrategy(int numBuffers) {
168 super.createBufferStrategy(numBuffers);
169 }
170
171 /**
172 * Creates a new strategy for multi-buffering on this component with the
173 * required buffer capabilities. This is useful, for example, if only
174 * accelerated memory or page flipping is desired (as specified by the
175 * buffer capabilities).
176 * <p>
177 * Each time this method
178 * is called, the existing buffer strategy for this component is discarded.
179 * @param numBuffers number of buffers to create
180 * @param caps the required capabilities for creating the buffer strategy;
181 * cannot be <code>null</code>
182 * @exception AWTException if the capabilities supplied could not be
183 * supported or met; this may happen, for example, if there is not enough
184 * accelerated memory currently available, or if page flipping is specified
185 * but not possible.
186 * @exception IllegalArgumentException if numBuffers is less than 1, or if
187 * caps is <code>null</code>
188 * @see #getBufferStrategy
189 * @since 1.4
190 */
191 public void createBufferStrategy(int numBuffers,
192 BufferCapabilities caps) throws AWTException {
193 super.createBufferStrategy(numBuffers, caps);
194 }
195
196 /**
197 * Returns the <code>BufferStrategy</code> used by this component. This
198 * method will return null if a <code>BufferStrategy</code> has not yet
199 * been created or has been disposed.
200 *
201 * @return the buffer strategy used by this component
202 * @see #createBufferStrategy
203 * @since 1.4
204 */
205 public BufferStrategy getBufferStrategy() {
206 return super.getBufferStrategy();
207 }
208
209 /*
210 * --- Accessibility Support ---
211 *
212 */
213
214 /**
215 * Gets the AccessibleContext associated with this Canvas.
216 * For canvases, the AccessibleContext takes the form of an
217 * AccessibleAWTCanvas.
218 * A new AccessibleAWTCanvas instance is created if necessary.
219 *
220 * @return an AccessibleAWTCanvas that serves as the
221 * AccessibleContext of this Canvas
222 * @since 1.3
223 */
224 public AccessibleContext getAccessibleContext() {
225 if (accessibleContext == null) {
226 accessibleContext = new AccessibleAWTCanvas();
227 }
228 return accessibleContext;
229 }
230
231 /**
232 * This class implements accessibility support for the
233 * <code>Canvas</code> class. It provides an implementation of the
234 * Java Accessibility API appropriate to canvas user-interface elements.
235 * @since 1.3
236 */
237 protected class AccessibleAWTCanvas extends AccessibleAWTComponent
238 {
239 private static final long serialVersionUID = -6325592262103146699L;
240
241 /**
242 * Get the role of this object.
243 *
244 * @return an instance of AccessibleRole describing the role of the
245 * object
246 * @see AccessibleRole
247 */
248 public AccessibleRole getAccessibleRole() {
249 return AccessibleRole.CANVAS;
250 }
251
252 } // inner class AccessibleAWTCanvas
253 }