teaching machines

CS 145 Lecture 14 – Logic Part Trois

October 3, 2014 by Chris Johnson. Filed under cs145, fall 2014, lectures.

Agenda

• what ?s
• Venn
• collision detection
• short circuiting

TODO

• Read section 5.3 in your book. 1/4 sheet.
• Start homework 3. Due before October 17. I’ve made some fixes to the specification and SpecChecker. You will need to sync through Bitbucket’s website and pull in Eclipse. Do not half-read this statement. Watch the lecture 2 video for a refresher.

Collision Detection

• What’s the signature for a method that can report whether or not two axis-aligned (non-rotated) rectangles are colliding?
• How can you implement that method?
• How are you thinking about this problem?
• Are you drawing pictures or tangible models? Are you scaling the problem back? Are you flipping the problem on its head?
• How can you tell if two pencils trapped in a tube are not colliding?
• How can you tell if two pencils trapped in a tube are colliding?
• How can you tell if two rectangular pieces of paper are colliding?
• How can you complete the original method?

Code

RectangleMover.java

package lecture1003;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.lang.ProcessBuilder.Redirect;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class RectangleMover extends JFrame {
  private Rectangle r1 = new Rectangle(50, 100, 100, 150);
  private Rectangle r2 = new Rectangle(300, 400, 200, 50);
  private Rectangle target;
  private Point downAt;

  public static void main(String[] args) {
    new RectangleMover();
  }

  public RectangleMover() {
    super("Rectangle Mover");
    add(new Panel());
    setSize(1000, 600);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
  }

  class Panel extends JPanel implements MouseListener, MouseMotionListener {
    public Panel() {
      addMouseListener(this);
      addMouseMotionListener(this);
    }
    
    @Override
    public void paintComponent(Graphics g) {
      super.paintComponent(g);

      g.setColor(RectangleUtilities.collides(r1.getMinX(), r1.getMaxX(), r1.getMinY(), r1.getMaxY(),
                                             r2.getMinX(), r2.getMaxX(), r2.getMinY(), r2.getMaxY()) ? Color.RED : Color.BLUE);

      g.fillRect(r1.x, r1.y, r1.width, r1.height);
      g.fillRect(r2.x, r2.y, r2.width, r2.height);
    }

    @Override
    public void mouseClicked(MouseEvent e) {
    }

    @Override
    public void mousePressed(MouseEvent e) {
      downAt = e.getPoint();
      if (r1.contains(e.getPoint())) {
        target = r1;
      } else if (r2.contains(e.getPoint())) {
        target = r2;
      } else {
        target = null;
      }
    }

    @Override
    public void mouseReleased(MouseEvent e) {
      target = null;
    }

    @Override
    public void mouseEntered(MouseEvent e) {
    }

    @Override
    public void mouseExited(MouseEvent e) {
    }

    @Override
    public void mouseDragged(MouseEvent e) {
      if (target != null) {
        target.translate(e.getPoint().x - downAt.x, e.getPoint().y - downAt.y);
        downAt = e.getPoint();
        repaint();
      }
    }

    @Override
    public void mouseMoved(MouseEvent e) {
    }
  }
}

RectangleUtilities.java

package lecture1003;

public class RectangleUtilities {
  public static boolean collides(double l1, double r1, double b1, double t1,
                                 double l2, double r2, double b2, double t2) {
    boolean isFree = r1 < l2 || r2 < l1 ||
                     t1 < b2 || t2 < b1;
    
    return !isFree;
  }
}

Haiku