gomp-20050608-branch/libjava/classpath/java/awt/Canvas.java

   1 /* Canvas.java --
   2    Copyright (C) 1999, 2000, 2002, 2004  Free Software Foundation
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.awt;
  40
  41 import java.awt.image.BufferStrategy;
  42 import java.awt.peer.ComponentPeer;
  43 import java.io.Serializable;
  44
  45 import javax.accessibility.Accessible;
  46 import javax.accessibility.AccessibleContext;
  47 import javax.accessibility.AccessibleRole;
  48
  49 /**
  50  * The <code>Canvas</code> component provides a blank rectangular
  51  * area, which the client application can use for drawing and for
  52  * capturing events.  By overriding the <code>paint()</code> method,
  53  * the canvas can be used for anything from simple line drawings to
  54  * full-scale custom components.
  55  *
  56  * @author Original author unknown
  57  * @author Tom Tromey  (tromey@redhat.com)
  58  * @author Andrew John Hughes  (gnu_andrew@member.fsf.org)
  59  * @since 1.0
  60  */
  61
  62 public class Canvas
  63   extends Component
  64   implements Serializable, Accessible
  65 {
  66
  67   /**
  68    * Compatible with Sun's JDK.
  69    */
  70   private static final long serialVersionUID = -2284879212465893870L;
  71
  72   /**
  73    * The graphics configuration associated with the canvas.
  74    */
  75   transient GraphicsConfiguration graphicsConfiguration;
  76
  77   /**
  78    * The buffer strategy associated with this canvas.
  79    */
  80   transient BufferStrategy bufferStrategy;
  81
  82   /**
  83    * Initializes a new instance of <code>Canvas</code>.
  84    */
  85   public Canvas()
  86   {
  87   }
  88
  89   /**
  90    * Initializes a new instance of <code>Canvas</code>
  91    * with the supplied graphics configuration.
  92    *
  93    * @param graphicsConfiguration the graphics configuration to use
  94    *        for this particular canvas.
  95    */
  96   public Canvas(GraphicsConfiguration graphicsConfiguration)
  97   {
  98     this.graphicsConfiguration = graphicsConfiguration;
  99   }
 100
 101   GraphicsConfiguration getGraphicsConfigurationImpl()
 102   {
 103     if (graphicsConfiguration != null)
 104       return graphicsConfiguration;
 105     return super.getGraphicsConfigurationImpl();
 106   }
 107
 108   /**
 109    * Creates the native peer for this object.
 110    */
 111   public void addNotify()
 112   {
 113     if (peer == null)
 114       peer = (ComponentPeer) getToolkit().createCanvas(this);
 115     super.addNotify();
 116   }
 117
 118   /**
 119    * Repaints the canvas window.  This method should be overridden by
 120    * a subclass to do something useful, as this method simply paints
 121    * the window with the background color.
 122    *
 123    * @param gfx the <code>Graphics</code> to use for painting
 124    */
 125   public void paint(Graphics gfx)
 126   {
 127     /* This implementation doesn't make much sense since the filling
 128       of background color is guaranteed for heavyweight components
 129       such as this.  But there's no need to worry, since paint() is
 130       usually overridden anyway.  */
 131     gfx.setColor(getBackground());
 132     Dimension size = getSize();
 133     gfx.fillRect(0, 0, size.width, size.height);
 134   }
 135
 136   /**
 137    * This class provides accessibility support for the canvas.
 138    */
 139   protected class AccessibleAWTCanvas
 140     extends AccessibleAWTComponent
 141   {
 142     /**
 143      * For compatability with Sun's JDK
 144      */
 145     private static final long serialVersionUID = -6325592262103146699L;
 146
 147     /**
 148      * Constructor for the accessible canvas.
 149      */
 150     protected AccessibleAWTCanvas()
 151     {
 152     }
 153
 154     /**
 155      * Returns the accessible role for the canvas.
 156      *
 157      * @return an instance of <code>AccessibleRole</code>, describing
 158      *         the role of the canvas.
 159      */
 160     public AccessibleRole getAccessibleRole()
 161     {
 162       return AccessibleRole.CANVAS;
 163     }
 164
 165   }
 166
 167   /**
 168    * Gets the AccessibleContext associated with this <code>Canvas</code>.
 169    * The context is created, if necessary.
 170    *
 171    * @return the associated context
 172    */
 173   public AccessibleContext getAccessibleContext()
 174   {
 175     /* Create the context if this is the first request */
 176     if (accessibleContext == null)
 177       accessibleContext = new AccessibleAWTCanvas();
 178     return accessibleContext;
 179   }
 180
 181   /**
 182    * A BltBufferStrategy for canvases.
 183    */
 184   private class CanvasBltBufferStrategy extends BltBufferStrategy
 185   {
 186     /**
 187      * Creates a block transfer strategy for this canvas.
 188      *
 189      * @param numBuffers the number of buffers in this strategy
 190      * @param accelerated true if the buffer should be accelerated,
 191      * false otherwise
 192      */
 193     CanvasBltBufferStrategy(int numBuffers, boolean accelerated)
 194     {
 195       super(numBuffers,
 196             new BufferCapabilities(new ImageCapabilities(accelerated),
 197                                    new ImageCapabilities(accelerated),
 198                                    BufferCapabilities.FlipContents.COPIED));
 199     }
 200   }
 201
 202   /**
 203    * A FlipBufferStrategy for canvases.
 204    */
 205   private class CanvasFlipBufferStrategy extends FlipBufferStrategy
 206   {
 207     /**
 208      * Creates a flip buffer strategy for this canvas.
 209      *
 210      * @param numBuffers the number of buffers in this strategy
 211      *
 212      * @throws AWTException if the requested number of buffers is not
 213      * supported
 214      */
 215     CanvasFlipBufferStrategy(int numBuffers)
 216       throws AWTException
 217     {
 218       super(numBuffers,
 219             new BufferCapabilities(new ImageCapabilities(true),
 220                                    new ImageCapabilities(true),
 221                                    BufferCapabilities.FlipContents.COPIED));
 222     }
 223   }
 224
 225   /**
 226    * Creates a buffering strategy that manages how this canvas is
 227    * repainted.  This method attempts to create the optimum strategy
 228    * based on the desired number of buffers.  Hardware or software
 229    * acceleration may be used.
 230    *
 231    * createBufferStrategy attempts different levels of optimization,
 232    * but guarantees that some strategy with the requested number of
 233    * buffers will be created even if it is not optimal.  First it
 234    * attempts to create a page flipping strategy, then an accelerated
 235    * blitting strategy, then an unaccelerated blitting strategy.
 236    *
 237    * Calling this method causes any existing buffer strategy to be
 238    * destroyed.
 239    *
 240    * @param numBuffers the number of buffers in this strategy
 241    *
 242    * @throws IllegalArgumentException if requested number of buffers
 243    * is less than one
 244    * @throws IllegalStateException if this canvas is not displayable
 245    *
 246    * @since 1.4
 247    */
 248   public void createBufferStrategy(int numBuffers)
 249   {
 250     if (numBuffers < 1)
 251       throw new IllegalArgumentException("Canvas.createBufferStrategy: number"
 252                                          + " of buffers is less than one");
 253
 254     if (!isDisplayable())
 255       throw new IllegalStateException("Canvas.createBufferStrategy: canvas is"
 256                                       + " not displayable");
 257
 258     BufferStrategy newStrategy = null;
 259
 260     // try a flipping strategy
 261     try
 262       {
 263         newStrategy = new CanvasFlipBufferStrategy(numBuffers);
 264       }
 265     catch (AWTException e)
 266       {
 267       }
 268
 269     // fall back to an accelerated blitting strategy
 270     if (newStrategy == null)
 271       newStrategy = new CanvasBltBufferStrategy(numBuffers, true);
 272
 273     bufferStrategy = newStrategy;
 274   }
 275
 276   /**
 277    * Creates a buffering strategy that manages how this canvas is
 278    * repainted.  This method attempts to create a strategy based on
 279    * the specified capabilities and throws an exception if the
 280    * requested strategy is not supported.
 281    *
 282    * Calling this method causes any existing buffer strategy to be
 283    * destroyed.
 284    *
 285    * @param numBuffers the number of buffers in this strategy
 286    * @param caps the requested buffering capabilities
 287    *
 288    * @throws AWTException if the requested capabilities are not
 289    * supported
 290    * @throws IllegalArgumentException if requested number of buffers
 291    * is less than one or if caps is null
 292    *
 293    * @since 1.4
 294    */
 295   public void createBufferStrategy(int numBuffers, BufferCapabilities caps)
 296     throws AWTException
 297   {
 298     if (numBuffers < 1)
 299       throw new IllegalArgumentException("Canvas.createBufferStrategy: number"
 300                                          + " of buffers is less than one");
 301
 302     if (caps == null)
 303       throw new IllegalArgumentException("Canvas.createBufferStrategy:"
 304                                          + " capabilities object is null");
 305
 306     // a flipping strategy was requested
 307     if (caps.isPageFlipping())
 308       bufferStrategy = new CanvasFlipBufferStrategy(numBuffers);
 309     else
 310       bufferStrategy = new CanvasBltBufferStrategy(numBuffers, true);
 311   }
 312
 313   /**
 314    * Returns the buffer strategy used by the canvas.
 315    *
 316    * @return the buffer strategy.
 317    * @since 1.4
 318    */
 319   public BufferStrategy getBufferStrategy()
 320   {
 321     return bufferStrategy;
 322   }
 323
 324   /**
 325    * Updates the canvas in response to a request to
 326    * <code>repaint()</code> it.  The canvas is cleared
 327    * with the current background colour, before <code>paint()</code>
 328    * is called to add the new contents.  Subclasses
 329    * which override this method should either call this
 330    * method via <code>super.update(graphics)</code> or re-implement
 331    * this behaviour, so as to ensure that the canvas is
 332    * clear before painting takes place.
 333    *
 334    * @param graphics the graphics context.
 335    */
 336   public void update(Graphics graphics)
 337   {
 338     Dimension size;
 339
 340     /* Clear the canvas */
 341     size = getSize();
 342     graphics.clearRect(0, 0, size.width, size.height);
 343     /* Call the paint method */
 344     paint(graphics);
 345   }
 346 }