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

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22 Advanced Object-Oriented Programming “ Do you ever think about things that you do think about? ” —Henry Drummond, Inherit the Wind In this chapter: – Encapsulation. – Inheritance. – Polymorphism. – Overloading. Advanced Object-Oriented Programming 409 In Chapter 8, we introduced object-oriented programming ( “ OOP ” ). Th e driving principle of the chapter was the pairing of data and functionality into one single idea, a class . A class is a template and from that template we made instances of objects and stored them in variables and arrays. Although we learned how to write classes and make objects, we did not delve very deeply into the core principles of OOP and explore its advanced features. Now that we are nearing the end of the book (and about to leap into the world of Java in the next chapter), it is a good time to refl ect on the past and take steps toward the future. Object-oriented programming in Processing and Java is defi ned by three fundamental concepts: encapsulation , inheritance , and polymorphism . We are familiar with encapsulation already; we just have not formalized our understanding of the concept and used the terminology. Inheritance and polymorphism are completely new concepts we will cover in this chapter. (At the end of this chapter, we will also take a quick look at method overloading , which allows objects to have more than one way of calling the constructor.) 22.1 Encapsulation To understand encapsulation , let’s return to the example of a Car class. And let’s take that example out into the world and think about a real-life Car object, operated by a real-life driver: you . It is a nice summer day and you are tired of programming and opt to head to the beach for the weekend. Traffi c permitting, you are hoping for a nice drive where you will turn the steering wheel a bunch of times, press on the gas and brakes, and fi ddle with dial on the radio. Th is car that you are driving is encapsulated . All you have to do to drive is operate the functions: steer( ) , gas( ) , brake( ) , and radio( ) . Do you know what is under the hood? How the catalytic converter connects to the engine or how the engine connects to the intercooler? What valves and wires and gears and belts do what? Sure, if you are an experienced auto mechanic you might be able to answer these questions, but the point is you don’t have to in order to drive the car. Th is is encapsulation . Encapsulation is defi ned as hiding the inner workings of an object from the user of that object.
410 Learning Processing In terms of object-oriented programming, the “ inner workings ” of an object are the data (variables of that object) and functions. Th e “ user ” of the object is you, the programmer, who is making object instances and using them throughout your code. Now, why is this a good idea? Chapter 8 (and all of the OOP examples throughout the book) emphasized the principles of modularity and reusability. Meaning, if you already fi gured out how to program a Car, why do it over and over again each time you have to make a Car? Just organize it all into the Car class, and you have saved yourself a lot of headaches. Encapsulation goes a step further. OOP does not just help you organize your code, it protects you from making mistakes . If you do not mess with the wiring of the car while you are driving it, you are less likely to break the car. Of course, sometimes a car breaks down and you need to fi x it, but this requires opening the hood and looking at the code inside the class itself. Take the following example. Let’s say you are writing a BankAccount class which has a fl oating point variable for the bank account balance . BankAccount account = new BankAccount(1000); A bank account object with a starting balance of $1,000. You will want to encapsulate that balance and keep it hidden. Why? Let’s say you need to withdraw money from that account. So you subtract $100 from that account. Withdrawing $100 by accessing account.balance = account.balance – 100. the balance variable directly. But what if there is a fee to withdraw money? Say, $1.25? We are going to get fi red from our bank programming job pretty quickly, having left this detail out. With encapsulation, we would keep our job, having written the following code instead. Withdrawing $100 by account.withdraw(100); calling a method! If the withdraw( ) function is written correctly, we will never forget the fee, since it will happen every single time the method is called. This function ensures that a void withdraw(float amount) { fee is also deducted whenever float fee = 1.25; the money is withdrawn. account – = (amount + fee); } Another benefi t of this strategy is that if the bank decides to raise the fee to $1.50, it can simply adjust the fee variable inside the BankAccount class and everything will keep working! Technically speaking, in order to follow the principles of encapsulation, variables inside of a class should never be accessed directly and can only be retrieved with a method. Th is is why you will often see programmers use a lot of functions known as getters and setters , functions that retrieve or change the value of variables. Here is an example of a Point class with two variables ( x and y ) that are accessed with getters and setters.
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Learning Processing A Beginner’s
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Learning Processing A Beginner’s
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Contents Acknowledgments vii Introd
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Acknowledgments In the fall of 2001
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Introduction What is this book? Th
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Introduction xi While both of these
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Introduction xiii Th e book is desi
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Introduction xv Th is book’s web
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Introductory Exercise: Write instru
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Lesson One The Beginning 1 Pixels 2
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1 Pixels “ A journey of a thousan
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1.2 Simple Shapes Pixels 5 Th e vas
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0 1 2 3 4 5 6 7 8 9 fi g. 1.9 top l
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1.3 Pixels 9 Exercise 1-3: Reverse
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Example 1-2: noFill ( ) background(
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fi g. 1.19 Pixels 13 Exercise 1-5:
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colorMode(RGB,100); Pixels 15 Th e
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2 2.1 Processing “ Computers in t
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fi g. 2.2 Once you have opened the
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Let’s write a fi rst example ( se
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Line 9 fi g. 2.6 Processing is case
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fi g. 2.7 Processing 25 Processing
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Example 2-1: Zoog again size(200,20
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Processing 29 To see the applet wor
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3 3.1 Interaction “ Always rememb
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Let’s look at what will surely be
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3.3 Variation with the Mouse Intera
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Draw Zoog's eyes fill(0); ellipse(8
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3.4 Mouse Clicks and Key Presses In
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Draw Zoog's eyes fill(mo useX,0,mou
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Lesson Two Everything You Need to K
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4 4.1 Variables “ All of the book
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4.2 Variable Declaration and Initia
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A variable can also be initialized
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x = 5; x = a + b; x = y - 10 * 20;
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void draw() { // Draw the backgroun
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4.6 Random: Variety is the spice of
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4.7 Example 4-7: Filling variables
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5 5.1 Conditionals Conditionals 59
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Finally, for testing multiple condi
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Conditionals 63 It is worth pointin
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Conditionals 65 Getting into the ha
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Our fi rst instinct might be to wri
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5.5 Multiple Rollovers Conditionals
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Conditionals 71 We can then check t
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5.7 Conditionals 73 Exercise 5-8: E
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Reversing the Polarity of a Number
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One way to solve this problem is to
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Display the square fill(0); noStrok
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6 Loops “ Repetition is the reali
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Loops 83 (see Chapter 5). However,
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while (y < 100) { // Loop! } 3. Wha
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while (x < = endLegs) { line(x,y,x,
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Th e same exact loop can be program
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Loops 91 Th is was a nice simplifi
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6.6 Loop Inside the Main Loop Loops
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6.7 float distance = abs(mouseX - i
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Draw Zoog's legs stroke(0); line(x-
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Lesson Three Organization 7 Functio
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7 7.1 Functions “ When it’s all
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7.2 “ User Defi ned ” Functions
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Example 5-6: Bouncing ball // Decla
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7.5 Functions 107 Exercise 7-3: Tak
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Functions 109 It should be fairly a
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int globalX = 0; int globalY = 100;
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void setup() { println( "a"); funct
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If we did not include a return stat
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7.8 Zoog Reorganization Zoog is now
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void draw() { } background(0); // D
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8 8.1 Objects “ No object is so b
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Setup: Draw: Initialize car color.
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Objects 125 • The Class Name—Th
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Objects 127 One other thing; with t
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fi g. 8.1 fi g. 8.2 fi g. 8.4 fi g.
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Objects 131 Nevertheless, this is q
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void draw() { } background(100); ba
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Objects 135 modular, reusable packa
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Lesson Three Project Step 1. Take y
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Lesson Four More of the Same 9 Arra
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9 Arrays “ I might repeat to myse
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Car myCar80 Car myCar81 Car myCar82
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9.3 Declaring and Creating an Array
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9.4 Initializing an Array One way t
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Example 9-5: Using a for loop to in
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Arrays 151 Now comes the hard part.
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9.7 Arrays 153 Exercise 9-7: Rewrit
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9.8 Interactive Objects Arrays 155
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Check if point is inside of Stripe
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alls[i].gravity(); balls[i].move();
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Draw Zoog's arms with a for loop fo
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Lesson Five Putting It All Together
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10 10.1 Algorithms “ Lather. Rins
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Translating the preceding algorithm
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void draw() { background(255); stro
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Example 10-2: Bouncing ball class c
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Now that the function is complete,
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10.6 // Constructor Ball(float temp
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Algorithms 177 With the above logic
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Drop() { r = 8; // All raindrops ar
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Example 10-7: Drops one at a time /
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Algorithms 183 Notice how every sin
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oolean intersecting = ball1.interse
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} void setLocation(float tempX, flo
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Algorithms 189 It is important to r
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11 Debugging “ Th e diff erence b
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Debugging 193 Once all the code is
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12 Libraries “ If truth is beauty
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or /Applications/Processing 0135/ c
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Lesson Six The World Revolves Aroun
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13 Mathematics Mathematics 201 “
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Mathematics 203 Th erefore, modulo
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Th e probability of a coin fl ippin
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13.6 Perlin Noise Mathematics 207 O
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Mathematics 209 How quickly we incr
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It is fairly intuitive for us to th
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fi g. 13.9 y-axis sine(theta) � y
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Example 13-6: Oscillation float the
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Mathematics 217 In 1975, Benoit Man
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Mathematics 219 said about recursio
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Mathematics 221 A two-dimensional a
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Example 13-10: Two-dimensional arra
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} void display() { } // FILL IN Mat
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14 14.1 Translation and Rotation (i
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Our fi rst instinct might be to add
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Example 14-3: A rectangle moving al
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When using the OPENGL mode, you mus
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Translation and Rotation (in 3D!) 2
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14.5 fill(150,150); vertex(-t, t,-t
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14.6 Example 14-5: Rectangle rotati
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fill(0,100); // Note the use of pus
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14.9 Example 14-17: Nested push and
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stroke(0); fill(175); ellipse(0,0,d
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Lesson Seven Pixels Under a Microsc
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15 Images Images 255 “ Politics w
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And yet: PImage img = loadImage( "f
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15.3 My Very First Image Processing
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Images 261 Even better, if we just
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Images 263 // Create a grayscale co
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Images 265 15.6 Intro to Image Proc
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Images 267 Since we are altering th
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15.9 More on fi lter( ): fi lter(mo
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Images 271 Example 15-13 performs a
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Example 15-14: “ Pointillism ”
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16 16.1 Video “ I have no memory.
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Video 277 Th e above line of code i
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void draw() { // Check to see if a
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16.3 Recorded Video Video 281 Displ
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16.4 Video 283 Exercise 16-3: Using
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Video 285 For every square at colum
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} } // Each rect is colored white w
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16.5 Video as Sensor, Computer Visi
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Now, we are ready to compare the co
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16.6 Video 293 Exercise 16-5: Take
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void setup() { size(320,240); video
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Example 16-13: Simple motion detect
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16.8 // Step 4, compare colors (pre
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Lesson Seven Project Develop a soft
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Lesson Eight The Outside World 17 T
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17 17.1 Text “ I could entertain
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Exercise 17-2: Loop through and pri
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17.3 Displaying Text Text 309 We wi
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println(PFont.list()); For demonstr
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X = �50 fi g. 17.4 float w = text
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Example 17-4: Text mirror import pr
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textFont(f); // Set the font transl
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Exercise 17-9: Using textWidth( ) ,
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Example 17-7: Boxes along a curve P
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Text 323 Exercise 17-10: Create a s
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18 Data Input “ A million monkeys
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Example 18-1: User input PFont f; /
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Data Input 329 Th e reverse of spli
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Example 18-2: Graphing comma separa
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Data Input 333 Th e rollover( ) fun
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18.4 diameter = diameter_; } // Tru
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} // Find the index of the end tag
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void mousePressed() { // Increment
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18.6 for (int i = 0; i < kinglear.l
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Create and make an asynchronous req
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� student � � id � 002 �
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Requests for XML data are made via
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18.8 Using the Processing XML Libra
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XMLElement diameterElement = childr
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Example 18-10: A Yahoo search impor
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However, if you request a URL on a
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19 19.1 Data Streams “ I’m mad
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Page 380 and 381: Data Streams 361 Once the server is
Page 382 and 383: 19.4 void draw() { background(255);
Page 384 and 385: Data Streams 365 must be networked
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Page 388 and 389: Data Streams 369 Here is the full S
Page 390 and 391: Here is the entire client sketch: 1
Page 392 and 393: Data Streams 373 Serial communicati
Page 394 and 395: Data Streams 375 of information, ca
Page 396 and 397: Corresponding Arduino code: int sen
Page 398 and 399: Lesson Nine Making Noise 20 Sound 2
Page 400 and 401: 20 Sound “ Check. Check. Check 1.
Page 402 and 403: void setup() { Sonia.start(this); }
Page 404 and 405: void mousePressed() { // If the use
Page 406 and 407: Sound 387 check and see if a sound
Page 408 and 409: Is a point inside the doorbell (use
Page 410 and 411: Pressing the mouse stops and starts
Page 412 and 413: 20.6 void draw() { background(255,1
Page 414 and 415: In code, this translates to: // If
Page 416 and 417: 21 Exporting “ Wait a minute. I t
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Page 420 and 421: void setup() { size(400, 400); begi
Page 422 and 423: Exporting 403 save( ) takes one arg
Page 424 and 425: Exporting 405 Example 21-5 records
Page 426 and 427: Lesson Ten Beyond Processing 22 Adv
Page 430 and 431: class Point { float x,y; Point(floa
Page 432 and 433: Advanced Object-Oriented Programmin
Page 434 and 435: Advanced Object-Oriented Programmin
Page 436 and 437: class Circle extends Shape { // inh
Page 438 and 439: for (int i = 0; i < dogs.length; i
Page 440 and 441: 22.5 Example 22-2: Polymorphism //
Page 442 and 443: 23 23.1 Java “ I l o ve c off ee,
Page 444 and 445: Java 425 instead of Processing , sp
Page 446 and 447: fi g. 23.2 Java 427 Just as with th
Page 448 and 449: Particle p = parray[i]; p.run(); p.
Page 450 and 451: Hint: Add a function that returns a
Page 452 and 453: Example 23-4: Super fancy ArrayList
Page 454 and 455: Java 435 It is sad when these error
Page 456 and 457: Th e tutorials will cover the same
Page 458 and 459: Appendix: Common Errors Appendix 43
Page 460 and 461: Error: No accessible fi eld named
Page 462 and 463: void draw() { thing.display(); } Co
Page 464 and 465: Error: Perhaps you wanted the overl
Page 466 and 467: Index AIFF (Audio Interchange File
Page 468 and 469: Fill( ) function 10 , 11 , 256 , 30
Page 470 and 471: One-dimensional Perlin noise 208 OP
Page 472: solar system, processing 247-9 vert
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