### Lesson Notes 30

— golan @ 4:45 am

Notes for 9/19

• modulo (%) arithmetic
• case, switch
• if/mouse: make a button
• click, set a boolean

The Trinary (or Ternary) Comparison Operator (see http://en.wikipedia.org/wiki/Ternary_operation):

```void setup() {
size(400, 200);
}

void draw() {
int g = (mouseX < 200) ? 0 : 255;
background (g);
}
```

Modulo Arithmetic: the % operator

```size(400, 100);

background(255);
for (int i=0; i
Trigger an event every N frames, using modulo arithmetic:
void setup() {
size(400, 100);
}

void draw() {
fill(0);

int x = frameCount % 100;
if (x == 0){
background(255,0,0);
text("bang!!", 200,50);

} else {
background(129);
text(x, 200,50);
}
}

Periodic movement (animation) using Modulo Arithmetic:
float x = 0;

void setup() {
size(400, 100);
}

void draw() {
background(255);
fill(0);

x = x + 2.7;
float pos = x % width;
ellipse (pos, 50, 20,20);
}

Periodic color animations with Modulo Arithmetic:
void setup() {
size(400, 150);
}

void draw() {

int moddedCounter = frameCount % 100;
float grayLevel = map(moddedCounter, 0,100, 0,255);
background(grayLevel);

fill (255-grayLevel);
text(moddedCounter, width/2, height/2);
}

Switch{} statement as alternative to a large number of if/else{}:
char theKey;

//=======================
void setup() {
size(400, 400);
}

//=======================
void keyPressed() {
theKey = key;
println("At " + millis() + " milliseconds, you pressed " + theKey);
}

//=======================
void draw() {
background(200);

switch (theKey) {

case 'e':
case 'E':
if (theKey == 'e') {
strokeWeight(1);
} else {
strokeWeight(5);
}
ellipse(200, 200, 100, 100);
break;

case 'r':
case 'R':
rect (100, 150, 200, 100);
break;

case 's':
rect (150, 150, 100, 100);
break;

default:
break;
}

}

Comparison: Random position, non-drunk walk:
void setup() {
size (300, 300);
}

void draw() {
background(200);

float rx;
float ry;
rx = width/2;
ry = height/2;

rx = rx + random(-10, 10);
ry = ry + random(-10, 10);
ellipse(rx, ry, 40, 40);
}

Comparison: Random position, drunk walk -- achieved through proper scoping of (persistent) variables:
float rx;
float ry;

void setup() {
size (300, 300);
rx = width/2;
ry = height/2;
}

void draw() {
background(200);
rx = rx + random(-10, 10);
ry = ry + random(-10, 10);
ellipse(rx, ry, 40, 40);
}

A simple toggle, achieved through negation of a boolean state variable:
boolean isTheBackgroundBlack;

void setup(){
size(200,200);
isTheBackgroundBlack = true;
}

void draw(){
if (isTheBackgroundBlack){
background(0,0,0);
} else {
background(255,200,200);
}
}

void mousePressed(){
isTheBackgroundBlack = ! isTheBackgroundBlack;
}

Detecting presence of the cursor in a rectangular region:
int buttL, buttR, buttW;
int buttT, buttB, buttH;

void setup(){
size(200,200);
buttT = 50;
buttL = 50;
buttH = 100;
buttW = 100;
buttR = buttL + buttW;
buttB = buttT + buttH;
}

void draw(){
background(128);

if ((mouseX > buttL) && (mouseX < buttR)  &&
(mouseY > buttT) && (mouseY < buttB)){
fill (0,250,250);
} else {
fill (255,255,255);
}

rect (buttL,buttT, buttW,buttH);
}

A toggling region ("on-screen button"):
boolean buttOff;
int buttL, buttR, buttW;
int buttT, buttB, buttH;

//------------------------------------
void setup(){
size(200,200);
buttOff = true;
buttT = buttL = 50;
buttH = buttW = 100;
buttR = buttL + buttW;
buttB = buttT + buttH;
}

//------------------------------------
void mousePressed(){
if ((mouseX > buttL) && (mouseX < buttR)  &&
(mouseY > buttT) && (mouseY < buttB)){
buttOff = !buttOff;
}
}

//------------------------------------
void draw(){
background(128);
color onColor   = color(0,255,255);  // cyan
color offColor  = color(0,0,0);      // black
color whatColorToUse = (buttOff) ? offColor : onColor; // trinary operator!
fill ( whatColorToUse );
rect(buttL,buttT, buttW,buttH);
}

```