Name: bk70084 Date: 06/23/98


/* What algorithm are you using to scan convert
 * ellipses/circles? It doesn't appear to be any of the
 * famous ones, e.g.: Pitteway, Van Aken, Kappel, Da Silva.
 * I am working on the next edition of the Addison-Wesley
 * textbook "Computer Graphics -- Fundamentals and
 * Practice", in which we use Java as the model graphics
 * package, and I am distressed at the poor quality of
 * filled ellipses/circles coming from JDK 1.2beta3. (I
 * refer to those rendered *without* antialiasing, which
 * allows me to see exactly what the rendering algorithm was
 * doing.)
 *
 * Generated circles/ellipses are strange in that the top
 * and left "sides" experience a kind of clipping that
 * yields a rather long portion which is essentially a
 * straight line segment. This doesn't happen on the right
 * and bottom "sides"; they look as though they were
 * generated by one of the famous algorithms.
 *
 * Attached is an applet that generates a number of filled
 * primitives. The white circle (atop a dark grey filled
 * ellipse) is the one that shows the problem best; look at
 * how non-symmetrical the circle's shape is on both the
 * vert and horiz axes. Note that the left "side" is the
 * worst of them; it looks as though clipping has occurred
 * (except for a 1-pixel "escape" exactly at the vertical
 * center).
 *
 * The grey filled ellipse arc's left "side" exhibits the
 * same "clip" problem exhibited in the white circle's left
 * side.
 *
 * Show the generated image to anyone who teaches computer
 * graphics rendering algorithms and I guarantee he/she will
 * cry "foul". There is definitely something wrong in the
 * scan conversion algorithm.
 *
 * Please note that I have not tested drawn (as opposed to
 * filled) circles/ellipses; it would be important for you
 * to ensure any fixes get translated into outline
 * generation as well, of course.
 *
 * Here's the code to my demo applet:
*/
import java.applet.Applet;
import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.awt.event.*;
import java.io.*;
import java.lang.*;
import java.net.*;

public class EArc extends Applet {
  static Frame appletFrame;
  BufferedImage offscrbuff;

  public synchronized void init() {
    System.out.println("java.version = " +
System.getProperty("java.version"));
    appletFrame = new Frame();
    appletFrame.setSize(600, 500);
    offscrbuff =
      new BufferedImage (600, 500, BufferedImage.TYPE_INT_ARGB/*_PRE*/);
    ppaint (offscrbuff.createGraphics());
  }

  public void stop() {
  }

  public void start() {
// appletFrame.pack();
try {
appletFrame.show();
} catch(NullPointerException e) {
System.out.println("Exception thrown by f.show(): "
+ e.getMessage());
e.printStackTrace();
}
  }

  public void destroy() {
  }


  public void update(Graphics g) {
  }

  public void paint(Graphics g) {
    g.drawImage(offscrbuff, 0, 0, this);
  }



  public void ppaint(Graphics g) {
    Graphics2D g2d = (Graphics2D)g;

    Polygon starshape = new Polygon();

    g2d.setStroke (new BasicStroke(2));

    //CONTROL IMAGE QUALITY
    //g2d.setRenderingHints (Graphics2D.ANTIALIASING, Graphics2D.ANTIALIAS_ON);
    g2d.setRenderingHints (Graphics2D.RENDERING, Graphics2D.RENDER_QUALITY);

    // FILL A STAR (a) WITH BLACK
    g2d.setColor (new Color(0,0,0));
    starshape.addPoint (80, 30);
    starshape.addPoint (30, 130);
    starshape.addPoint (130, 60);
    starshape.addPoint (30, 60);
    starshape.addPoint (130, 130);
    g2d.fill (starshape);

    // FILL A PIESLICE (b) WITH DARK GREY
    g2d.setColor (new Color(150,150,150));
    g2d.fillArc (150,60, 130,75, 45, 270);

    // FILL A CIRCLE (c) IN WHITE
    g2d.setColor (new Color(255,255,255));
    g2d.fillOval (165,80, 40,40);

    // FILL A RECTANGLE (d) WITH MEDIUM GREY
    g2d.setColor (new Color(180,180,180));
    g2d.fill (new Rectangle(200,30, 80,50));

    // FILL (e) WITH SAME COLOR BUT IN TRANSLUCENT MODE
    AlphaComposite acDestOverTranslu =
      AlphaComposite.getInstance(AlphaComposite.DST_OVER, (float)0.65);
    g2d.setComposite(acDestOverTranslu);
    g2d.fill (new Rectangle(200,115, 80,50));
  }

  public String getAppletInfo() {
    return "Filled shapes";
  }
      
  public String[][] getParameterInfo() {
    String[][] info = {};
    return info;
  }

  public static void main (String[] args) {
    Applet theApplet = new EArc();

    theApplet.init();

    //appletFrame.pack();
    appletFrame.add(theApplet, "Center");

    appletFrame.setLocation(140,100);
    appletFrame.addWindowListener( new AppQuitter());

    theApplet.start();
    theApplet.stop();
    theApplet.destroy();

  } // end "public static void main"

  /*
   * An inner class for quitting the application
   */
  static class AppQuitter extends WindowAdapter {
    public void windowClosing(WindowEvent e) {
      e.getWindow().dispose();
      System.exit(0);
    } // end "public void windowClosing"
  } // end "static class AppQuitter"
} // End "public class EArc extends Applet"
(Review ID: 34052)
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