Lecture Notes Five: Anatomy of a Simple Networked Game

Before Spring Break we will have a complete 3D game working.

Meanwhile we need to keep working at the basics.

Besides trying to understand App3DCore we also want to finish the Hockey game.

We will add a puck and implement collisions today.

Here's also a game like Jason wants to implement.

You can find it in

/l/www/classes/a348/t540/lectures/Cannon

The URL for this game is on the What's New? page.

Let's start from a basic working version of the Hockey program.

I am putting the starting point in

/l/www/classes/a348/t540/lectures/Hockey

frilled.cs.indiana.edu%pwd
/nfs/grouchy/home/user2/www/classes/a348-dger/t540/lectures/Hockey
frilled.cs.indiana.edu%du -a
4	./ChatClient.java
1	./.java.policy
1	./ClientExports.java
3	./ChatServer.java
1	./Player.java
3	./ChatClient.class
1	./ServerExports.java
1	./ClientExports.class
1	./Player.class
1	./ServerExports.class
3	./ChatServer.class
3	./ChatClient_Stub.class
2	./ChatClient_Skel.class
4	./ChatServer_Stub.class
2	./ChatServer_Skel.class
32	.
frilled.cs.indiana.edu%

Here's how you get all you need.

burrowww.cs.indiana.edu% pwd
/nfs/paca/home/user1/dgerman/pucka
burrowww.cs.indiana.edu% cp /l/www/classes/a348/t540/lectures/Hockey/* .
burrowww.cs.indiana.edu% du -a . 
3       ./ChatClient.class
4       ./ChatClient.java
2       ./ChatClient_Skel.class
3       ./ChatClient_Stub.class
3       ./ChatServer.class
3       ./ChatServer.java
2       ./ChatServer_Skel.class
4       ./ChatServer_Stub.class
1       ./ClientExports.class
1       ./ClientExports.java
1       ./Player.class
1       ./Player.java
1       ./ServerExports.class
1       ./ServerExports.java
31      .
burrowww.cs.indiana.edu% cp /l/www/classes/a348/t540/lectures/Hockey/.jav* ~
burrowww.cs.indiana.edu% ls -ld ~/.jav*
-rw-r--r--   1 dgerman  faculty        73 Feb 21 11:07 /u/dgerman/.java.policy
burrowww.cs.indiana.edu% cat ~/.jav*
grant {
  permission java.net.SocketPermission "*", "connect,accept";
};
burrowww.cs.indiana.edu% 

• connect to tucotuco, molerat, blesmol
• start the server on one, and the client on the other two
• use 39xxx as the port number to make sure we don't run into conflicts

Once we are sure this works, let's start making the changes.

We want the server to move a Puck around.

So we make the changes,

import java.rmi.*;
// ... 

public class ChatServer extends UnicastRemoteObject 
                        implements ServerExports {
    
    // ... 
    
    Puck puck; 

    // ... 
    
    public ChatServer() throws RemoteException {
        // ... 
	puck = new Puck(ChatClient.WIDTH, ChatClient.HEIGHT, this); 
	System.out.println("Puck has been initialized... "); 
	puck.start(); 
    }
    
    // ... 

}

class Puck extends Thread {
    int width, height;
    ChatServer server; 
    Puck(int w, int h, ChatServer s) {
	width = w; height = h; 
        server = s; 
    }
    public void run() {
	while (true) {
	    try {

		System.out.println("I am the puck..."); 
		Thread.sleep(1000); 

	    } catch(Exception e) {

	    }
	}
    }
}

tucotuco.cs.indiana.edu% pwd
/nfs/paca/home/user1/dgerman/pucka
tucotuco.cs.indiana.edu% javac *.java
Note: ChatClient.java uses or overrides a deprecated API.  Recompile with "-deprecation" for details.
1 warning
tucotuco.cs.indiana.edu% rmic ChatClient
tucotuco.cs.indiana.edu% rmic ChatServer
tucotuco.cs.indiana.edu%

class Puck extends Thread {
    int width, height;
    int x, y; 
    ChatServer server; 
    Puck(int w, int h, ChatServer s) {
	width = w; height = h; 
	server = s; 
    }
    public void run() {
	while (true) {
	    try {
		System.out.println("I am the puck..." + this.report()); 
		this.move(); 
		Thread.sleep(1000); 

	    } catch(Exception e) {

	    }
	}
    }
    int dx = 3, dy = 3; 
    public void move() {
	x += dx; 
	y += dy; 
	if (x < 0) { x = 0; dx = -dx; } 
	else if (x > width) { x = width; dx = -dx; } 
	if (y < 0) { y = 0; dy = -dy; } 
	else if (y > height) { y = height; dy = -dy; } 

    }
    public String report() {
	return "(" + this.x + ", " + this.y + ")"; 
    }
}

// ... 

public class ChatServer extends UnicastRemoteObject 
                        implements ServerExports {

    // ...     

    public void notify(int x, int y) {
	System.out.println("I am the server, the puck's at: (" + 
			   x + ", " + y + ")"); 
	for (int i = 0; i <= size; i++) {
	    // check for collisions with players[i] 
	}

	for (int i = 0; i <= size; i++) {
	    try { 
		clients[i].updatePuckPosition(x, y); 
	    } catch (Exception e) {

	    }
	}

    }
    
    // ... 

}

class Puck extends Thread {

    // ...

    public String report() {
	server.notify(x, y); 
	return "(" + this.x + ", " + this.y + ")"; 
    }

    // ... 
}

// ... 

public class ChatClient extends Frame implements ClientExports, 
						 KeyListener {

    // ... 

    public void updatePuckPosition(int x, int y) {
	System.out.println("I am a client, the puck is at: (" + 
			   x + ", " + y + ")"); 
    }
    
    // ... 

}

// ... 

public interface ClientExports extends Remote {
    // ...
    public void updatePuckPosition(int x, int y) throws RemoteException; 
}

I'll explain the last part in class.

I will also use the following notes:

http://www.cs.indiana.edu/classes/a348/t540/lectures/Feb21.html

The final code is in

/l/www/classes/a348/t540/lectures/ten/hockey