Package org.jcsp.awt

Class ActiveCanvas

java.lang.Object
java.awt.Component
java.awt.Canvas
org.jcsp.awt.ActiveCanvas
All Implemented Interfaces:
ImageObserver, MenuContainer, Serializable, Accessible, CSProcess
public class ActiveCanvas extends Canvas implements CSProcess
java.awt.Canvas with a channel interface.

Process Diagram

Description

ActiveCanvas is a process extension of java.awt.Canvas with channels for run-time configuration/interrogation and event notification. The event channels should be connected to one or more application-specific server. processes (instead of registering a passive object as a Listener to this component).

All channels are optional. The toGraphics/fromGraphics channels are set by calling the setGraphicsChannels method. Event channels can be added to notify the occurrence of any type of Event the component generates by calling the appropriate addXXXEventChannel method. All channel connections must be made before the process is run.

Messages can be sent down the toGraphics channel at any time to configure or interrogate the component. A reply or acknowledgment is returned down the fromGraphics channel and must be read. See the table below and GraphicsProtocol for details.

Graphics operations on an ActiveCanvas are most conveniently managed by attaching, and then setting GraphicsCommands on, a DisplayList (or any user-defined object implementing the Paintable interface). This can be done either statically via the setPaintable method, or dynamically via the toGraphics/fromGraphics channels (see GraphicsProtocol.SetPaintable).

All channels are managed by independent internal handler processes. It is, therefore, safe for a serial application process both to service an event channel and configure the component -- no deadlock can occur.

IMPORTANT: it is essential that event channels from this process are always serviced -- otherwise the Java Event Thread will be blocked and the GUI will stop responding. A simple way to guarantee this is to use channels configured with overwriting buffers. For example: 

   final One2OneChannel myMouseEvent = Channel.one2one (new OverWriteOldestBuffer (n));
 
   final ActiveCanvas myCanvas = new ActiveCanvas ();
   myCanvas.addMouseEventChannel (myMouseEvent.out ());
This will ensure that the Java Event Thread will never be blocked. Slow or inattentive readers may miss rapidly generated events, but the n most recent events will always be available.

Channel Protocols

Input Channels
displayList GraphicsCommand[] See DisplayList and GraphicsCommand.
toGraphics GraphicsProtocol See GraphicsProtocol.
Output Channels
fromGraphics Object Response to the fromGraphics message. See the documentation on GraphicsProtocol.
componentEvent ComponentEvent See the addComponentEventChannel method.
focusEvent FocusEvent See the addFocusEventChannel method.
keyEvent KeyEvent See the addKeyEventChannel method.
mouseEvent MouseEvent See the addMouseEventChannel method.
mouseMotionEvent MouseEvent See the addMouseMotionEventChannel method.

Example

 import java.awt.*;
 import java.awt.event.*;
 import org.jcsp.lang.*;
 import org.jcsp.util.*;
 import org.jcsp.awt.*;
 
 public class ActiveCanvasExample {
 
   public static void main (String argv[]) {
 
     final ActiveClosingFrame activeClosingFrame =
       new ActiveClosingFrame ("ActiveCanvas Example");
     final Frame frame = activeClosingFrame.getActiveFrame ();
 
     final One2OneChannel mouseEvent = Channel.one2one (new OverWriteOldestBuffer (10));
 
     final DisplayList displayList = new DisplayList ();
 
     final ActiveCanvas canvas = new ActiveCanvas ();
     canvas.addMouseEventChannel (mouseEvent.out ());
     canvas.setPaintable (displayList);
     canvas.setSize (600, 400);
 
     frame.add (canvas);
     frame.pack ();
     frame.setVisible (true);
 
     new Parallel (
       new CSProcess[] {
         activeClosingFrame,
         canvas,
         new CSProcess () {
           public void run () {
             final String clickMessage = "D O U B L E - C L I C K   T H E   M O U S E   T O   E X I T";
             final String clickPlea = "       P L E A S E   M O V E   T H E   M O U S E   B A C K    ";
             final GraphicsCommand[] mouseEntered =
               {new GraphicsCommand.SetColor (Color.cyan),
                new GraphicsCommand.FillRect (0, 0, 600, 400),
                new GraphicsCommand.SetColor (Color.black),
                new GraphicsCommand.DrawString (clickMessage, 140, 200)};
             final GraphicsCommand[] mouseExited =
               {new GraphicsCommand.SetColor (Color.pink),
                new GraphicsCommand.FillRect (0, 0, 600, 400),
                new GraphicsCommand.SetColor (Color.black),
                new GraphicsCommand.DrawString (clickPlea, 140, 200)};
             final GraphicsCommand mousePressed =
               new GraphicsCommand.DrawString (clickMessage, 160, 220);
             final GraphicsCommand mouseReleased =
               new GraphicsCommand.DrawString (clickMessage, 140, 200);
             displayList.set (mouseExited);
             boolean running = true;
             while (running) {
               final MouseEvent event = (MouseEvent) mouseEvent.in ().read ();
               switch (event.getID ()) {
                 case MouseEvent.MOUSE_ENTERED:
                   System.out.println ("MOUSE_ENTERED");
                   displayList.set (mouseEntered);
                 break;
                 case MouseEvent.MOUSE_EXITED:
                   System.out.println ("MOUSE_EXITED");
                   displayList.set (mouseExited);
                 break;
                 case MouseEvent.MOUSE_PRESSED:
                   System.out.println ("MOUSE_PRESSED");
                   displayList.change (mousePressed, 3);
                 break;
                 case MouseEvent.MOUSE_RELEASED:
                   System.out.println ("MOUSE_RELEASED");
                   displayList.change (mouseReleased, 3);
                 break;
                 case MouseEvent.MOUSE_CLICKED:
                   if (event.getClickCount() > 1) {
                     System.out.println ("MOUSE_DOUBLE_CLICKED ... goodbye!");
                     running = false;
                   }
                 break;
               }
             }
             frame.setVisible (false);
             System.exit (0);
           }
         }
       }
     ).run ();
   }
 
 }
See Also:

  • Field Details

    • toGraphics

      private ChannelInput toGraphics

    • fromGraphics

      private ChannelOutput fromGraphics

    • paintable

      private Paintable paintable

    • vec

      private Vector vec
      The Vector construct containing the handlers.

    • requestedWidth

      private int requestedWidth

    • requestedHeight

      private int requestedHeight

  • Constructor Details

    • ActiveCanvas

      public ActiveCanvas()

  • Method Details

    • setGraphicsChannels

      public void setGraphicsChannels(ChannelInput toGraphics, ChannelOutput fromGraphics)
      Set the toGraphics/fromGraphics channels for configuring and/or examining this component. A org.jcsp.awt.GraphicsProtocol object sent down the toGraphics channel generates the appropriate configuration or enquiry action. A reply object is always returned down the fromGraphics channel.

      NOTE: This method must be called before this process is run.

      Parameters:
      toGraphics - the channel down which GraphicsProtocol objects are sent.
      fromGraphics - the reply/acknowledgement channel responding to the GraphicsProtocol object.

    • setPaintable

      public void setPaintable(Paintable paintable)
      Set the Paintable object that will be used by the paint and update methods of this canvas. If paintable is null, the paint/update methods will not be overriden.

      JCSP provides a DisplayList as an example Paintable class. This can be thought of as a special form of channel. A user process at the other end writes to it by setting up and/or editing an ordered list of GraphicsCommands. This method may be used to connect the DisplayList to this ActiveCanvas. For example: 

         final ActiveCanvas myActiveCanvas = new ActiveCanvas ();
   
   final DisplayList draw = new DisplayList ();
   myActiveCanvas.setPaintable (draw);
   
   ...  connect other channels (toGraphics, fromGraphics, mouseEvent, etc.)
   
   // myActiveCanvas is now ready to run

      NOTE: If setPaintable is going to be invoked, this must happen before this process is run.

      Alternatively, the Paintable object may be set dynamically by sending an appropriate GraphicsProtocol.SetPaintable object down the toGraphics channel.

      Parameters:
      paintable - the object to be used for painting/updating the canvas.

    • paint

      public void paint(Graphics g)
      This method is used by the JVM event thread -- it is not really for public consumption. If setPaintable has been invoked on this canvas or a GraphicsProtocol.SetPaintable object has been sent down the toGraphics channel, this method uses the supplied Paintable object to do the painting.

      Overrides:
      paint in class Canvas

    • update

      public void update(Graphics g)
      This method is used by the JVM event thread -- it is not really for public consumption. If setPaintable has been invoked on this canvas or a GraphicsProtocol.SetPaintable object has been sent down the toGraphics channel, this method uses the supplied Paintable object to do the updating.

      Overrides:
      update in class Canvas

    • addComponentEventChannel

      public void addComponentEventChannel(ChannelOutput componentEvent)
      Add a new channel to this component that will be used to notify that a ComponentEvent has occurred. This should be used instead of registering a ComponentListener with the component. It is possible to add more than one Channel by calling this method multiple times If the channel passed is null, no action will be taken.

      NOTE: This method must be called before this process is run.

      Parameters:
      componentEvent - the channel down which to send ComponentEvents.

    • addFocusEventChannel

      public void addFocusEventChannel(ChannelOutput focusEvent)
      Add a new channel to this component that will be used to notify that a FocusEvent has occurred. This should be used instead of registering a FocusListener with the component. It is possible to add more than one Channel by calling this method multiple times If the channel passed is null, no action will be taken.

      NOTE: This method must be called before this process is run.

      Parameters:
      focusEvent - the channel down which to send FocusEvents.

    • addKeyEventChannel

      public void addKeyEventChannel(ChannelOutput keyEvent)
      Add a new channel to this component that will be used to notify that a KeyEvent has occurred. This should be used instead of registering a KeyListener with the component. It is possible to add more than one Channel by calling this method multiple times If the channel passed is null, no action will be taken.

      NOTE: This method must be called before this process is run.

      Parameters:
      keyEvent - the channel down which to send KeyEvents.

    • addMouseEventChannel

      public void addMouseEventChannel(ChannelOutput mouseEvent)
      Add a new channel to this component that will be used to notify that a MouseEvent has occurred. This should be used instead of registering a MouseListener with the component. It is possible to add more than one Channel by calling this method multiple times If the channel passed is null, no action will be taken.

      NOTE: This method must be called before this process is run.

      Parameters:
      mouseEvent - the channel down which to send MouseEvents.

    • addMouseMotionEventChannel

      public void addMouseMotionEventChannel(ChannelOutput mouseMotionEvent)
      Add a new channel to this component that will be used to notify that a MouseMotionEvent has occurred. This should be used instead of registering a MouseMotionListener with the component. It is possible to add more than one Channel by calling this method multiple times If the channel passed is null, no action will be taken.

      NOTE: This method must be called before this process is run.

      Parameters:
      mouseMotionEvent - the channel down which to send MouseMotionEvents.

    • setSize

      public void setSize(int requestedWidth, int requestedHeight)
      Request that the canvas takes the size given by the parameters. The methods getPreferredSize and getMinimumSize are overridden to return these dimensions.

      NOTE: This method must be called before this process is run.

      Overrides:
      setSize in class Component
      Parameters:
      requestedWidth - the requested width for the canvas.
      requestedHeight - the requested height for the canvas.

    • getPreferredSize

      public Dimension getPreferredSize()
      This method is used by system classes -- it is not really for public consumption!

      Overrides:
      getPreferredSize in class Component

    • getMinimumSize

      public Dimension getMinimumSize()
      This method is used by system classes -- it is not really for public consumption!

      Overrides:
      getMinimumSize in class Component

    • run

      public void run()
      The main body of this process.
      Specified by:
      run in interface CSProcess