Learning Processing Example 7-4 Suggested Change Corrected (2nd edition, p. 123)

example_07_03_modularity.pde

// Learning Processing
// Daniel Shiffman
// http://www.learningprocessing.com

// Example 7-3: Bouncing ball with functions

// Declare all global variables (stays the same)
int x = 0;
int speed = 1;

// Setup does not change
void setup() {
  size(480, 270);
}

void draw() {
  background(255);
  move(); // Instead of writing out all the code about the ball is draw(), we simply call three functions. How do we know the names of these functions? We made them up!
  bounce();
  // display(); // display ball, it's the original
  display_smiley(); // display smiley instead
}

// Where should functions be placed?
// You can define your functions anywhere in the code outside of setup() and draw().
// However, the convention is to place your function definitions below draw().

// A function to move the ball
void move() {
  // Change the x location by speed
  x = x + speed;
}

// A function to bounce the ball
void bounce() {
  // If we’ve reached an edge, reverse speed
  if ((x > width) || (x < 0)) {
    speed = speed * - 1;
  }
}

// A function to display the ball
void display() {
  stroke(0);
  fill(175);
  ellipse(x,height/2,32,32);
}

// A function to display a rectangular smiley instead
void display_smiley() {
  float y = height/2; // this declaration of Y is needed but not printed in the book!
  background(255);
  rectMode(CENTER);
  noFill();
  stroke(0);
  rect(x,y,32,32); // will fail without declaration of Y
  fill(255);
  rect(x-4, y-4, 4, 4); // will fail without declaration of Y
  rect(x+4, y-4, 4, 4); // will fail without declaration of Y
  line(x-4, y+4, x+4, y+4); // will fail without declaration of Y
}