Learning Processing: A Beginner's Guide to Programming Images ...

366 Learning Processing
19.5
Example 19-5: Client reading values as rotation value
// Import the net libraries
import processing.net.*;
// Declare a client
Client client;
// The data we will read from the server
int data;
void setup() {
size(200,200);
smooth();
// Create the Client
client = new Client(this, " 127.0.0.1 " , 5204);
}
void draw() {
if (client.available() > 0) {
data = client.read(); // Read data
}
background(255);
stroke(0);
fill(175);
translate(width/2,height/2);
float theta = (data/255.0) * TWO_PI;
rotate(theta);
rectMode(CENTER);
rect(0,0,64,64);
}
The incoming data is
used to rotate a square.
Exercise 19-3: Write a client that uses the number broadcast from the server to control the
location of a shape.
Multi-User Communication, Part 1: The Server
Th e broadcast example demonstrates one-way communication where a server broadcasts a message and
many clients receive that message. Th e broadcast model, however, does not allow a client to turn around
and send a reply back to the server. In this section, we will cover how to create a sketch that involves
communication between multiple clients facilitated by a server.
Let’s explore how a chat room works. Five clients (you and four friends) connect to a server. One client
types a message: “ Hey everyone! ” Th at message is sent to the server, which relays it back to all fi ve clients.
Most multi-user applications function in a similar fashion. A multiplayer online game, for example,
would likely have clients sending information related to their whereabouts and actions to a server that
broadcasts that data back to all other clients playing the game.
A multi-user application can be developed in Processing using the network library. To demonstrate, we
will create a networked, shared whiteboard. As a client drags its mouse around the screen, the sketch