# teaching machines

## CS 145 Lecture 15 – More colliding

October 31, 2011 by . Filed under cs145, fall 2011, lectures.

### Agenda

• meet JFrame and company
• collide circles
• collide rectangles

### Code

#### CollisionUtilities.java

package lecture;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class CollisionUtilities {

public static void main(String[] args) throws FileNotFoundException {
Scanner in = new Scanner(new File("/home/cjohnson/Desktop/lines.txt"));

while (in.hasNextDouble()) {
double leftA = in.nextDouble();
double rightA = in.nextDouble();
double leftB = in.nextDouble();
double rightB = in.nextDouble();
boolean expected = in.nextBoolean();

boolean actual = isColliding(leftA, rightA, leftB, rightB);
if (actual != expected) {
System.out.printf("[%f, %f] vs. [%f, %f] expected: " + expected + ", actual: " + actual + "%n", leftA, rightA, leftB, rightB);
}
}

in.close();
}

/**
* Checks whether two 1-D line segments intersect.
*
* @param leftA
* Left bounds of line segment A, assumed < rightA
* @param rightA
* Right bounds of line segment A
* @param leftB
* Left bounds of line segment B, assumed < rightB
* @param rightB
* Right bounds of line segment B
* @return True if they collide, false otherwise
*/
public static boolean isColliding(double leftA,
double rightA,
double leftB,
double rightB) {
return !(leftB > rightA || rightB < leftA);
}

/**
* Checks whether two circles intersect.
* @param xA X-coordinate of circle A's center
* @param yA Y-coordinate of circle A's center
* @param radiusA Radius of circle A
* @param xB X-coordinate of circle B's center
* @param yB Y-coordinate of circle B's center
* @param radiusB Radius of circle B
* @returns True if colliding, false otherwise
*/
public static boolean isColliding(double xA,
double yA,
double radiusA,
double xB,
double yB,
double radiusB) {
double distance = Math.sqrt(Math.pow(yA - yB, 2) + Math.pow(xA - xB, 2));
return distance <= radiusA + radiusB;
}
}

#### ColliderPanel.java

package lecture;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class ColliderPanel extends JPanel implements MouseMotionListener {
public static void main(String[] args) {
JFrame frame = new JFrame("Collision");
frame.add(new ColliderPanel());
frame.setSize(512, 512);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}

private int leftA = 200;
private int rightA = 300;

private int leftB;
private int rightB;

private int xA = 200;
private int yA = 300;
private int radiusA = 75;

private int xB;
private int yB;
private int radiusB = 50;

/**
* Creates a new canvas for testing collision detection. It tracks its own
* mouse movement.
*/
public ColliderPanel() {
addMouseMotionListener(this);
}

/**
* Draws the canvas. TODO: have it draw in red when the shapes collide.
*
* @param g
* The drawing canvas
*/
public void paintComponent(Graphics g) {
g.clearRect(0, 0, getWidth(), getHeight());

// if colliding, color chartreuse
// // otherwise black

// if (CollisionUtilities.isColliding(leftA, rightA, leftB, rightB)) {
// // g.setColor(new Color(236, 235, 189));
// g.setColor(Color.PINK);
// } else {
// g.setColor(Color.BLACK);
// }
//
// g.drawLine(leftA, 300, rightA, 300);
// g.drawLine(leftB, 300, rightB, 300);

//
if (CollisionUtilities.isColliding(xA, yA, radiusA, xB, yB, radiusB)) {
g.setColor(new Color(236, 235, 189));
g.setColor(Color.PINK);
} else {
g.setColor(Color.BLACK);
}
//
g.fillOval(xA - radiusA, yA - radiusA, radiusA * 2, radiusA * 2);
g.fillOval(xB - radiusB, yB - radiusB, radiusB * 2, radiusB * 2);
}

/**
* Handles mouse drag (i.e., a button is down) by ignoring them.
*
* @param event
* Mouse drag event
*/
public void mouseDragged(MouseEvent event) {
}

/**
* Handles mouse motion when no button is down. We simply update the current
* mouse position and redraw the canvas so that colliding object is drawn in
* the new position.
*
* @param event
* Mouse motion event
*/
public void mouseMoved(MouseEvent event) {
leftB = event.getX() - 50;
rightB = leftB + 100;

xB = event.getX();
yB = event.getY();

repaint();
}
}

### TODO

• Read section 7.1.

### Haiku

When I code, I’m king
Booleans express my will
Scanner, watch yourself