Scribble.java

// Smooth Scribble
// see http://c2.com/~ward/java/Scribble.html

import java.applet.*;
import java.awt.*;

public class Scribble extends Applet implements Runnable {
  private double cx = 0, cy = 0;	// current x, y
  private int fx, fy;			// final x, y
  private Thread coast = null;

  double smooth(double p, double q) {
    return (.8 * p) + (.2 * q);
  }

  void stop() {
    if ((coast != null) && coast.isAlive())
      coast.stop();
    coast = null;
  }

  boolean mouseDown(Event e, int x, int y) {
    this.stop();
    cx = x; cy = y;
    return true;
  }

  public synchronized boolean mouseDrag(Event e, int x, int y) {
    Graphics g = getGraphics();
    double nx = smooth(cx, x);		// next x, y
    double ny = smooth(cy, y);
    g.drawLine((int)cx, (int)cy, (int)nx, (int)ny);
    cx = nx; cy = ny;
    return true;
  }

  boolean mouseUp(Event e, int x, int y) {
    fx = x; fy = y;
    if (coast==null) {
      coast = new Thread(this);
      coast.start();
    }
    return true;
  }

  void run() {
    while(true) {
      mouseDrag(null, fx, fy);
      Thread.sleep(50);
    }
  }
}