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ScribblePane.javaAPI DocExample4158Sat Jan 24 10:44:32 GMT 2004je3.gui

ScribblePane

public class ScribblePane extends JComponent
This custom component allows the user to scribble, and retains the scribbles so that they can be redrawn when needed. It uses the PolyLine custom Shape implementation defined elsewhere in this book, and demonstrates event handling with low-level event processing methods.

Fields Summary
List
lines
je3.graphics.PolyLine
currentLine
Stroke
stroke
Constructors Summary
public ScribblePane()

	setPreferredSize(new Dimension(450,200)); // We need a default size
	lines = new ArrayList();                  // Initialize a list of lines
	stroke = new BasicStroke(3.0f);           // Lines are 3 pixels wide

	// Register interest in mouse button and mouse motion events, so
	// that processMouseEvent() and processMouseMotionEvent() will be 
	// invoked, even if no event listeners are registered.
	enableEvents(AWTEvent.MOUSE_EVENT_MASK |
		     AWTEvent.MOUSE_MOTION_EVENT_MASK);
Methods Summary
public voidclear()
Erase all lines and repaint. This method is for the convenience of programs that use this component.

	lines.clear();
	repaint();
public voidpaintComponent(java.awt.Graphics g)
We override this method to draw ourselves.

	// Let the superclass do its painting first
	super.paintComponent(g);

	// Make a copy of the Graphics context so we can modify it
	// We cast it at the same time so we can use Java2D graphics
	Graphics2D g2 = (Graphics2D) (g.create()); 

	// Our superclass doesn't paint the background, so do this ourselves.
	g2.setColor(getBackground());
	g2.fillRect(0, 0, getWidth(), getHeight());

	// Set the line width and color to use for the foreground
	g2.setStroke(stroke);
	g2.setColor(this.getForeground());

	// Now loop through the PolyLine shapes and draw them all
	int numlines = lines.size();
	for(int i = 0; i < numlines; i++)
	    g2.draw((PolyLine)lines.get(i));
public voidprocessMouseEvent(java.awt.event.MouseEvent e)
We override this method to receive notification of mouse button events. See also the enableEvents() call in the constructor method.

	// If the type and button are correct, then process it.
	if (e.getButton() == MouseEvent.BUTTON1) {
	    if (e.getID() == MouseEvent.MOUSE_PRESSED) {
		// Start a new line on mouse down
		currentLine = new PolyLine(e.getX(), e.getY());
		lines.add(currentLine);
		e.consume();
	    }
	    else if (e.getID() == MouseEvent.MOUSE_RELEASED) {
		// End the line on mouse up
		currentLine = null;
		e.consume();
	    }
	}

	// The superclass method dispatches to registered event listeners
	super.processMouseEvent(e);
public voidprocessMouseMotionEvent(java.awt.event.MouseEvent e)
We override this method to receive notification of mouse motion events.

	if (e.getID() == MouseEvent.MOUSE_DRAGGED && // If we're dragging
	    currentLine != null) {                   // and a line exists
	    currentLine.addSegment(e.getX(), e.getY());  // Add a line segment
	    e.consume();

	    // Redraw the whole component.
	    // Exercise: optimize this by passing the bounding box
	    // of the region that needs redrawing to the repaint() method.
	    // Don't forget to take line width into account, however.
	    repaint();
	}

	super.processMouseMotionEvent(e);