Learning Processing: Chapter 5: Example 5-4: Hold Down the Button

Example

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

// Example 5-4: Hold down the button
boolean button = false;

int x = 50;
int y = 50;
int w = 100;
int h = 75;

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

void draw() {
  // The button is pressed if (mouseX,mouseY) is inside the rectangle and mousePressed is true.
  if (mouseX > x && mouseX < x+w && mouseY > y && mouseY < y+h && mousePressed) {
    button = true; 
  } else {
    button = false;
  }

 if (button) {
    background(255);
    stroke(0);
  } else {
    background(0);
    stroke(255);
  }
  
  fill(175);
  rect(x,y,w,h);
}

Comments (7)

http://www.mimran.com&patrickmimran.com Patrick Mimran

i would like to understand something please , if a boolean is anyway only t or false why do we have to specify
true or false when we declare the variable name in this example .
Or if flase is specified when variable is declared why shouldn’t we write only “button” instead of button = false when button false ?

Thank you

Patrick
http://www.learningprocessing.com Daniel Shiffman

Yes, the default value of a boolean variable is false. So

boolean button = false;

and

boolean button;

are the same. However, it’s a good habit to always initialize your variables, just so that your code is more clear.
http://www.mimran.com&patrickmimran.com Patrick Mimran

Thank you very much

Patrick
mhelke

what if I want to have more than one of these rectangles?
I tried this but it doesn’t work…// Learning Processing
// Daniel Shiffman
// http://www.learningprocessing.com

// Example 5-4: Hold down the button
boolean button1 = false;

int x = 800;
int y = 230;
int w = 10;
int h = 10;

boolean button2 = false;
int x1 = 200;
int y1 = 230;
int w1 = 10;
int h1 = 10;

PImage b;
PImage c;
PImage d;
PImage e;

void setup() {
size(960,540);
noStroke();
}

void draw() {
// The button is pressed if (mouseX,mouseY) is inside the rectangle and mousePressed is true.
if (mouseX > x && mouseX y && mouseY x && mouseX y && mouseY < y1+h1 && mousePressed) {
button2 = true;
} else {
button2 = false;
}

if (button1) {
b = loadImage("first.gif");
background(b);
noStroke();
} else {
c = loadImage("second.gif");
background(c);

}

if (button2) {
d = loadImage("first.jpeg");
background(d);
noStroke();
} else {
e = loadImage("second.jpeg");
background(e);

}

fill(#e09554);
rect(x,y,w,h);
rect(x1,y1,w1,h1);
}
Anonymous

your second conditional needs to reference x1, not x. Also, you’ll want to use an if, else if, else structure, i.e.

if (button1) {
background(0,255,0);
} else if (button2) {
background(255,0,0);
} else {
background(0,0,255);
}

Object-oriented programming will really make this easier. See:

http://www.learningprocessing.com/exercises/chapter-9/exercise-9-8/
http://profiles.google.com/will.price94 Will Price

For this bit ” if(button) ”
why does it not read “if(button == true)”
Anonymous

These are equivalent. if (button) is simple a shorter way of writing it. Since a boolean variable can only be “true” or “false” by definition, asking if it is equal to true is redundant.