import javax.swing.; import java.awt.; import java.awt.event.; 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("Grid", 500, 500, 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 objects; private HashMap 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); frame.addWindowListener( new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } } );

canvas.setPreferredSize(new Dimension(width, height)); backgroundColour = bgColour; frame.pack(); objects = new ArrayList(); shapes = new HashMap(); }

/* 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(); }

/* 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); } }

}