Initial revision

From-SVN: r102074

libjava/classpath/java/awt/Canvas.java

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+/* Canvas.java --
+   Copyright (C) 1999, 2000, 2002, 2004  Free Software Foundation
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath 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 for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package java.awt;
+
+import java.awt.image.BufferStrategy;
+import java.awt.peer.ComponentPeer;
+import java.io.Serializable;
+
+import javax.accessibility.Accessible;
+import javax.accessibility.AccessibleContext;
+import javax.accessibility.AccessibleRole;
+
+/**
+ * The <code>Canvas</code> component provides a blank rectangular
+ * area, which the client application can use for drawing and for
+ * capturing events.  By overriding the <code>paint()</code> method,
+ * the canvas can be used for anything from simple line drawings to
+ * full-scale custom components.
+ *
+ * @author Original author unknown
+ * @author Tom Tromey  (tromey@redhat.com)
+ * @author Andrew John Hughes  (gnu_andrew@member.fsf.org)
+ * @since 1.0
+ */
+
+public class Canvas
+  extends Component
+  implements Serializable, Accessible
+{
+
+  /**
+   * Compatible with Sun's JDK.
+   */
+  private static final long serialVersionUID = -2284879212465893870L;
+
+  /**
+   * The graphics configuration associated with the canvas.
+   */
+  transient GraphicsConfiguration graphicsConfiguration;
+
+  /**
+   * The buffer strategy associated with this canvas.
+   */
+  transient BufferStrategy bufferStrategy;
+
+  /**
+   * Initializes a new instance of <code>Canvas</code>.
+   */
+  public Canvas() 
+  { 
+  }
+
+  /**
+   * Initializes a new instance of <code>Canvas</code>
+   * with the supplied graphics configuration.
+   *
+   * @param graphicsConfiguration the graphics configuration to use
+   *        for this particular canvas.
+   */
+  public Canvas(GraphicsConfiguration graphicsConfiguration)
+  {
+    this.graphicsConfiguration = graphicsConfiguration;
+  }
+
+  GraphicsConfiguration getGraphicsConfigurationImpl()
+  {
+    if (graphicsConfiguration != null)
+      return graphicsConfiguration;
+    return super.getGraphicsConfigurationImpl();
+  }
+
+  /**
+   * Creates the native peer for this object.
+   */
+  public void addNotify()
+  {
+    if (peer == null)
+      peer = (ComponentPeer) getToolkit().createCanvas(this);
+    super.addNotify();
+  }
+
+  /**
+   * Repaints the canvas window.  This method should be overridden by 
+   * a subclass to do something useful, as this method simply paints
+   * the window with the background color.
+   *
+   * @param gfx the <code>Graphics</code> to use for painting
+   */
+  public void paint(Graphics gfx)
+  {
+    /* This implementation doesn't make much sense since the filling
+      of background color is guaranteed for heavyweight components
+      such as this.  But there's no need to worry, since paint() is
+      usually overridden anyway.  */
+    gfx.setColor(getBackground());
+    Dimension size = getSize();
+    gfx.fillRect(0, 0, size.width, size.height);
+  }
+
+  /**
+   * This class provides accessibility support for the canvas.
+   */
+  protected class AccessibleAWTCanvas
+    extends AccessibleAWTComponent
+  {
+    /**
+     * For compatability with Sun's JDK
+     */
+    private static final long serialVersionUID = -6325592262103146699L;
+
+    /**
+     * Constructor for the accessible canvas.
+     */
+    protected AccessibleAWTCanvas()
+    {
+    }
+
+    /**
+     * Returns the accessible role for the canvas.
+     *
+     * @return an instance of <code>AccessibleRole</code>, describing
+     *         the role of the canvas.
+     */
+    public AccessibleRole getAccessibleRole()
+    {
+      return AccessibleRole.CANVAS;
+    }
+    
+  }
+
+  /**
+   * Gets the AccessibleContext associated with this <code>Canvas</code>.
+   * The context is created, if necessary.
+   *
+   * @return the associated context
+   */
+  public AccessibleContext getAccessibleContext()
+  {
+    /* Create the context if this is the first request */
+    if (accessibleContext == null)
+      accessibleContext = new AccessibleAWTCanvas();
+    return accessibleContext;
+  }
+
+  /**
+   * A BltBufferStrategy for canvases.
+   */
+  private class CanvasBltBufferStrategy extends BltBufferStrategy
+  {
+    /**
+     * Creates a block transfer strategy for this canvas.
+     *
+     * @param numBuffers the number of buffers in this strategy
+     * @param accelerated true if the buffer should be accelerated,
+     * false otherwise
+     */
+    CanvasBltBufferStrategy(int numBuffers, boolean accelerated)
+    {
+      super(numBuffers,
+	    new BufferCapabilities(new ImageCapabilities(accelerated),
+				   new ImageCapabilities(accelerated),
+				   BufferCapabilities.FlipContents.COPIED));
+    }
+  }
+
+  /**
+   * A FlipBufferStrategy for canvases.
+   */
+  private class CanvasFlipBufferStrategy extends FlipBufferStrategy
+  {
+    /**
+     * Creates a flip buffer strategy for this canvas.
+     *
+     * @param numBuffers the number of buffers in this strategy
+     *
+     * @throws AWTException if the requested number of buffers is not
+     * supported
+     */
+    CanvasFlipBufferStrategy(int numBuffers)
+      throws AWTException
+    {
+      super(numBuffers,
+	    new BufferCapabilities(new ImageCapabilities(true),
+				   new ImageCapabilities(true),
+				   BufferCapabilities.FlipContents.COPIED));
+    }
+  }
+
+  /**
+   * Creates a buffering strategy that manages how this canvas is
+   * repainted.  This method attempts to create the optimum strategy
+   * based on the desired number of buffers.  Hardware or software
+   * acceleration may be used.
+   *
+   * createBufferStrategy attempts different levels of optimization,
+   * but guarantees that some strategy with the requested number of
+   * buffers will be created even if it is not optimal.  First it
+   * attempts to create a page flipping strategy, then an accelerated
+   * blitting strategy, then an unaccelerated blitting strategy.
+   *
+   * Calling this method causes any existing buffer strategy to be
+   * destroyed.
+   *
+   * @param numBuffers the number of buffers in this strategy
+   *
+   * @throws IllegalArgumentException if requested number of buffers
+   * is less than one
+   * @throws IllegalStateException if this canvas is not displayable
+   *
+   * @since 1.4
+   */
+  public void createBufferStrategy(int numBuffers)
+  {
+    if (numBuffers < 1)
+      throw new IllegalArgumentException("Canvas.createBufferStrategy: number"
+					 + " of buffers is less than one");
+
+    if (!isDisplayable())
+      throw new IllegalStateException("Canvas.createBufferStrategy: canvas is"
+				      + " not displayable");
+
+    BufferStrategy newStrategy = null;
+
+    // try a flipping strategy
+    try
+      {
+	newStrategy = new CanvasFlipBufferStrategy(numBuffers);
+      }
+    catch (AWTException e)
+      {
+      }
+
+    // fall back to an accelerated blitting strategy
+    if (newStrategy == null)
+      newStrategy = new CanvasBltBufferStrategy(numBuffers, true);
+
+    bufferStrategy = newStrategy;
+  }
+
+  /**
+   * Creates a buffering strategy that manages how this canvas is
+   * repainted.  This method attempts to create a strategy based on
+   * the specified capabilities and throws an exception if the
+   * requested strategy is not supported.
+   *
+   * Calling this method causes any existing buffer strategy to be
+   * destroyed.
+   *
+   * @param numBuffers the number of buffers in this strategy
+   * @param caps the requested buffering capabilities
+   *
+   * @throws AWTException if the requested capabilities are not
+   * supported
+   * @throws IllegalArgumentException if requested number of buffers
+   * is less than one or if caps is null
+   *
+   * @since 1.4
+   */
+  public void createBufferStrategy(int numBuffers,
+				   BufferCapabilities caps)
+  {
+    if (numBuffers < 1)
+      throw new IllegalArgumentException("Canvas.createBufferStrategy: number"
+					 + " of buffers is less than one");
+
+    if (caps == null)
+      throw new IllegalArgumentException("Canvas.createBufferStrategy:"
+					 + " capabilities object is null");
+
+    // a flipping strategy was requested
+    if (caps.isPageFlipping())
+      {
+	try
+	  {
+	    bufferStrategy = new CanvasFlipBufferStrategy(numBuffers);
+	  }
+	catch (AWTException e)
+	  {
+	  }
+      }
+    else
+      bufferStrategy = new CanvasBltBufferStrategy(numBuffers, true);
+  }
+
+  /**
+   * Returns the buffer strategy used by the canvas.
+   *
+   * @return the buffer strategy.
+   * @since 1.4
+   */
+  public BufferStrategy getBufferStrategy()
+  {
+    return bufferStrategy;
+  }
+
+  /**
+   * Updates the canvas in response to a request to
+   * <code>repaint()</code> it.  The canvas is cleared
+   * with the current background colour, before <code>paint()</code>
+   * is called to add the new contents.  Subclasses
+   * which override this method should either call this
+   * method via <code>super.update(graphics)</code> or re-implement
+   * this behaviour, so as to ensure that the canvas is
+   * clear before painting takes place.
+   *
+   * @param graphics the graphics context.
+   */
+  public void update(Graphics graphics)
+  {
+    Dimension size;
+
+    /* Clear the canvas */
+    size = getSize();
+    graphics.clearRect(0, 0, size.width, size.height);
+    /* Call the paint method */
+    paint(graphics);
+  }
+}