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

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5 5.1 Conditionals Conditionals 59 “ Th at language is an instrument of human reason, and not merely a medium for the expression of thought, is a truth generally admitted. ” —George Boole “ Th e way I feel about music is that there is no right and wrong. Only true and false. ” —Fiona Apple In this chapter: – Boolean expressions. – Conditional statements: How a program produces different results based on varying circumstances. – If, Else If, Else . Boolean Expressions What’s your favorite kind of test? Essay format? Multiple choice? In the world of computer programming, we only take one kind of test: a boolean test—true or false. A boolean expression (named for mathematician George Boole) is an expression that evaluates to either true or false. Let’s look at some common language examples: • I am hungry. → true • I am afraid of computer programming. → false • This book is a hilarious read. → false In the formal logic of computer science, we test relationships between numbers. • 15 is greater than 20 → false • 5 equals 5 → true • 32 is less than or equal to 33 → true In this chapter, we will learn how to use a variable in a boolean expression, allowing our sketch to take diff erent paths depending on the current value stored in the variable. • x � 20 → depends on current value of x • y � � 5 → depends on current value of y • z � � 33 → depends on current value of z Th e following operators can be used in a boolean expression. Relational Operators � greater than � � less than or equal to � less than � � equality � � greater than or equal to ! � inequality
60 Learning Processing 5.2 Conditionals: If, Else, Else If Boolean expressions (often referred to as “ conditionals ” ) operate within the sketch as questions. Is 15 greater than 20? If the answer is yes (i.e., true), we can choose to execute certain instructions (such as draw a rectangle); if the answer is no (i.e., false), those instructions are ignored. Th is introduces the idea of branching; depending on various conditions, the program can follow diff erent paths. In the physical world, this might amount to instructions like so: If I am hungry then eat some food, otherwise if I am thirsty, drink some water, otherwise, take a nap . In Processing , we might have something more like: If the mouse is on the left side of the screen, draw a rectangle on the left side of the screen . Or, more formally, with the output shown in Figure 5.1 , if (mouseX < width/2) { fill(255); rect(0,0,width/2,height); } Th e boolean expression and resulting instructions in the above source code is contained within a block of code with the following syntax and structure: if (boolean expression) { // code to execute if boolean expression is true } Th e structure can be expanded with the keyword else to include code that is executed if the boolean expression is false. Th is is the equivalent of “ otherwise, do such and such. ” if (boolean expression) { // code to execute if boolean expression is true } else { // code to execute if boolean expression is false } For example, we could say the following, with the output shown in Figure 5.2 . If the mouse is on the left side of the screen, draw a white background, otherwise draw a black background . if (mouseX < width/2) { background(255); } else { background(0); } fi g. 5.2 fi g. 5.1
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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
Page 28 and 29: 1.3 Pixels 9 Exercise 1-3: Reverse
Page 30 and 31: Example 1-2: noFill ( ) background(
Page 32 and 33: fi g. 1.19 Pixels 13 Exercise 1-5:
Page 34 and 35: colorMode(RGB,100); Pixels 15 Th e
Page 36 and 37: 2 2.1 Processing “ Computers in t
Page 38 and 39: fi g. 2.2 Once you have opened the
Page 40 and 41: Let’s write a fi rst example ( se
Page 42 and 43: Line 9 fi g. 2.6 Processing is case
Page 44 and 45: fi g. 2.7 Processing 25 Processing
Page 46 and 47: Example 2-1: Zoog again size(200,20
Page 48 and 49: Processing 29 To see the applet wor
Page 50 and 51: 3 3.1 Interaction “ Always rememb
Page 52 and 53: Let’s look at what will surely be
Page 54 and 55: 3.3 Variation with the Mouse Intera
Page 56 and 57: Draw Zoog's eyes fill(0); ellipse(8
Page 58 and 59: 3.4 Mouse Clicks and Key Presses In
Page 60 and 61: Draw Zoog's eyes fill(mo useX,0,mou
Page 62 and 63: Lesson Two Everything You Need to K
Page 64 and 65: 4 4.1 Variables “ All of the book
Page 66 and 67: 4.2 Variable Declaration and Initia
Page 68 and 69: A variable can also be initialized
Page 70 and 71: x = 5; x = a + b; x = y - 10 * 20;
Page 72 and 73: void draw() { // Draw the backgroun
Page 74 and 75: 4.6 Random: Variety is the spice of
Page 76 and 77: 4.7 Example 4-7: Filling variables
Page 80 and 81: Finally, for testing multiple condi
Page 82 and 83: Conditionals 63 It is worth pointin
Page 84 and 85: Conditionals 65 Getting into the ha
Page 86 and 87: Our fi rst instinct might be to wri
Page 88 and 89: 5.5 Multiple Rollovers Conditionals
Page 90 and 91: Conditionals 71 We can then check t
Page 92 and 93: 5.7 Conditionals 73 Exercise 5-8: E
Page 94 and 95: Reversing the Polarity of a Number
Page 96 and 97: One way to solve this problem is to
Page 98 and 99: Display the square fill(0); noStrok
Page 100 and 101: 6 Loops “ Repetition is the reali
Page 102 and 103: Loops 83 (see Chapter 5). However,
Page 104 and 105: while (y < 100) { // Loop! } 3. Wha
Page 106 and 107: while (x < = endLegs) { line(x,y,x,
Page 108 and 109: Th e same exact loop can be program
Page 110 and 111: Loops 91 Th is was a nice simplifi
Page 112 and 113: 6.6 Loop Inside the Main Loop Loops
Page 114 and 115: 6.7 float distance = abs(mouseX - i
Page 116 and 117: Draw Zoog's legs stroke(0); line(x-
Page 118 and 119: Lesson Three Organization 7 Functio
Page 120 and 121: 7 7.1 Functions “ When it’s all
Page 122 and 123: 7.2 “ User Defi ned ” Functions
Page 124 and 125: Example 5-6: Bouncing ball // Decla
Page 126 and 127: 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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import processing.net.* ; Server se
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Data Streams 361 Once the server is
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19.4 void draw() { background(255);
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Data Streams 365 must be networked
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Data Streams 367 will send X , Y co
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Data Streams 369 Here is the full S
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Here is the entire client sketch: 1
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Data Streams 373 Serial communicati
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Data Streams 375 of information, ca
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Corresponding Arduino code: int sen
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Lesson Nine Making Noise 20 Sound 2
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20 Sound “ Check. Check. Check 1.
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void setup() { Sonia.start(this); }
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void mousePressed() { // If the use
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Sound 387 check and see if a sound
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Is a point inside the doorbell (use
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Pressing the mouse stops and starts
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20.6 void draw() { background(255,1
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In code, this translates to: // If
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21 Exporting “ Wait a minute. I t
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Th is code can be inserted anywhere
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void setup() { size(400, 400); begi
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Exporting 403 save( ) takes one arg
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Exporting 405 Example 21-5 records
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Lesson Ten Beyond Processing 22 Adv
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22 Advanced Object-Oriented Program
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class Point { float x,y; Point(floa
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Advanced Object-Oriented Programmin
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Advanced Object-Oriented Programmin
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class Circle extends Shape { // inh
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for (int i = 0; i < dogs.length; i
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22.5 Example 22-2: Polymorphism //
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23 23.1 Java “ I l o ve c off ee,
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Java 425 instead of Processing , sp
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fi g. 23.2 Java 427 Just as with th
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Particle p = parray[i]; p.run(); p.
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Hint: Add a function that returns a
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Example 23-4: Super fancy ArrayList
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Java 435 It is sad when these error
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Th e tutorials will cover the same
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Appendix: Common Errors Appendix 43
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Error: No accessible fi eld named
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void draw() { thing.display(); } Co
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Error: Perhaps you wanted the overl
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Index AIFF (Audio Interchange File
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Fill( ) function 10 , 11 , 256 , 30
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One-dimensional Perlin noise 208 OP
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solar system, processing 247-9 vert
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