uni

Canvas.java (7181B)

---

 import javax.swing.*;
 import java.awt.*;
 import java.util.List;
 import java.util.*; 
 
 /**
  * Canvas is a class to allow for simple graphical drawing on a canvas.
  * This is a modification of the general purpose Canvas, specially made for
  * the BlueJ "shapes" example. 
  *
  * @author: Bruce Quig
  * @author: Michael Kolling (mik)
  *
  * @version: 1.6 (shapes)
  */
 public class Canvas
 {
     // Note: The implementation of this class (specifically the handling of
     // shape identity and colors) is slightly more complex than necessary. This
     // is done on purpose to keep the interface and instance fields of the
     // shape objects in this project clean and simple for educational purposes.
 
 	private static Canvas canvasSingleton;
 
 	/**
 	 * Factory method to get the canvas singleton object.
 	 */
 	public static Canvas getCanvas()
 	{
 		if(canvasSingleton == null) {
 			canvasSingleton = new Canvas("BlueJ Shapes Demo", 300, 300, 
 										 Color.white);
 		}
 		canvasSingleton.setVisible(true);
 		return canvasSingleton;
 	}
 
 	//  ----- instance part -----
 
     private JFrame frame;
     private CanvasPane canvas;
     private Graphics2D graphic;
     private Color backgroundColour;
     private Image canvasImage;
     private List<Object> objects;
     private HashMap<Object,Object> shapes;
     
     /**
      * Create a Canvas.
      * @param title  title to appear in Canvas Frame
      * @param width  the desired width for the canvas
      * @param height  the desired height for the canvas
      * @param bgClour  the desired background colour of the canvas
      */
     private Canvas(String title, int width, int height, Color bgColour)
     {
         frame = new JFrame();
         canvas = new CanvasPane();
         frame.setContentPane(canvas);
         frame.setTitle(title);
         canvas.setPreferredSize(new Dimension(width, height));
         backgroundColour = bgColour;
         frame.pack();
         frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
         objects = new ArrayList<Object>();
         shapes = new HashMap<Object,Object> ();
     }
 
     /**
      * Set the canvas visibility and brings canvas to the front of screen
      * when made visible. This method can also be used to bring an already
      * visible canvas to the front of other windows.
      * @param visible  boolean value representing the desired visibility of
      * the canvas (true or false) 
      */
     public void setVisible(boolean visible)
     {
         if(graphic == null) {
             // first time: instantiate the offscreen image and fill it with
             // the background colour
             Dimension size = canvas.getSize();
             canvasImage = canvas.createImage(size.width, size.height);
             graphic = (Graphics2D)canvasImage.getGraphics();
             graphic.setColor(backgroundColour);
             graphic.fillRect(0, 0, size.width, size.height);
             graphic.setColor(Color.black);
         }
         frame.setVisible(visible);
     }
 
     /**
      * Draw a given shape onto the canvas.
      * @param  referenceObject  an object to define identity for this shape
      * @param  color            the color of the shape
      * @param  shape            the shape object to be drawn on the canvas
      */
      // Note: this is a slightly backwards way of maintaining the shape
      // objects. It is carefully designed to keep the visible shape interfaces
      // in this project clean and simple for educational purposes.
     public void draw(Object referenceObject, String color, Shape shape)
     {
     	objects.remove(referenceObject);   // just in case it was already there
     	objects.add(referenceObject);      // add at the end
     	shapes.put(referenceObject, new ShapeDescription(shape, color));
     	redraw();
     }
  
     /**
      * Erase a given shape's from the screen.
      * @param  referenceObject  the shape object to be erased 
      */
     public void erase(Object referenceObject)
     {
     	objects.remove(referenceObject);   // just in case it was already there
     	shapes.remove(referenceObject);
     	redraw();
     }
 
     /**
      * Set the foreground colour of the Canvas.
      * @param  newColour   the new colour for the foreground of the Canvas 
      */
     public void setForegroundColor(String colorString)
     {
 		if(colorString.equals("red"))
 			graphic.setColor(Color.red);
 		else if(colorString.equals("black"))
 			graphic.setColor(Color.black);
 		else if(colorString.equals("blue"))
 			graphic.setColor(Color.blue);
 		else if(colorString.equals("yellow"))
 			graphic.setColor(Color.yellow);
 		else if(colorString.equals("green"))
 			graphic.setColor(Color.green);
 		else if(colorString.equals("magenta"))
 			graphic.setColor(Color.magenta);
 		else if(colorString.equals("white"))
 			graphic.setColor(Color.white);
 		else
 			graphic.setColor(Color.black);
     }
 
     /**
      * Wait for a specified number of milliseconds before finishing.
      * This provides an easy way to specify a small delay which can be
      * used when producing animations.
      * @param  milliseconds  the number 
      */
     public void wait(int milliseconds)
     {
         try
         {
             Thread.sleep(milliseconds);
         } 
         catch (Exception e)
         {
             // ignoring exception at the moment
         }
     }
 
 	/**
 	 * Redraw ell shapes currently on the Canvas.
 	 */
 	private void redraw()
 	{
 		erase();
 		for(Iterator i=objects.iterator(); i.hasNext(); ) {
             ((ShapeDescription)shapes.get(i.next())).draw(graphic);
         }
         canvas.repaint();
     }
     
     /**
      * Get the width
      */
     public int getWidth(){
         return canvas.getWidth();
     }
     
     /**
      * Get the height
      */
     public int getHeight(){
         return canvas.getHeight();
     }
        
     /**
      * Erase the whole canvas. (Does not repaint.)
      */
     private void erase()
     {
         Color original = graphic.getColor();
         graphic.setColor(backgroundColour);
         Dimension size = canvas.getSize();
         graphic.fill(new Rectangle(0, 0, size.width, size.height));
         graphic.setColor(original);
     }
 
 
     /************************************************************************
      * Inner class CanvasPane - the actual canvas component contained in the
      * Canvas frame. This is essentially a JPanel with added capability to
      * refresh the image drawn on it.
      */
     private class CanvasPane extends JPanel
     {
         public void paint(Graphics g)
         {
             g.drawImage(canvasImage, 0, 0, null);
         }
     }
     
     /************************************************************************
      * Inner class CanvasPane - the actual canvas component contained in the
      * Canvas frame. This is essentially a JPanel with added capability to
      * refresh the image drawn on it.
      */
     private class ShapeDescription
     {
     	private Shape shape;
     	private String colorString;
 
 		public ShapeDescription(Shape shape, String color)
     	{
     		this.shape = shape;
     		colorString = color;
     	}
 
 		public void draw(Graphics2D graphic)
 		{
 			setForegroundColor(colorString);
 			graphic.fill(shape);
 		}
     }
 
 }