Learning Processing: Chapter 5: Example 5-3: Rollovers

Example

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

// Example 5-3: Rollovers
void setup() {
  size(200,200);
}

void draw() {
  background(255);
  stroke(0);
  line(100,0,100,200);
  line(0,100,200,100);
  
  // Fill a black color
  noStroke();
  fill(0);

  // Depending on the mouse location, a different rectangle is displayed.    
  if (mouseX < 100 && mouseY < 100) {
    rect(0,0,100,100);
  } else if (mouseX > 100 && mouseY < 100) {
    rect(100,0,100,100);
  } else if (mouseX < 100 && mouseY > 100) {
    rect(0,100,100,100);
  } else if (mouseX > 100 && mouseY > 100) {
    rect(100,100,100,100);
  }
}

Comments (3)

Kit

After a 20 year break from programming this excercise really grabbed my interest. After doing it as above I tried nested if statements (If mouse on left side of screen then if mouse at top of screen etc.) This didn’t make it any prettier.

Then I remembered you could do this

x=(width/2)*int(mouseX>width/2);
y=(height/2)*int(mouseY > height/2);
rect(x,y,width/2,height/2);

What fun!
http://www.mimran.com&patrickmimran.com Patrick Mimran

I did this exercise only with ifs first i thought i made a mistake but it worked as well i am wondering what is the plus to use if else ?

Thanks

PM

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

void draw() {
background(255);
stroke(0);
line(100,0,100,200);
line(0,100,200,100);

// Fill a black color
noStroke();
fill(0);

// Depending on the mouse location, a different rectangle is displayed.
if (mouseX < 100 && mouseY 100 && mouseY < 100) {
rect(100,0,100,100); }
if (mouseX 100) {
rect(0,100,100,100);}
if (mouseX > 100 && mouseY > 100) {
rect(100,100,100,100);
}
}
http://www.learningprocessing.com Daniel Shiffman
In this case, it doesn’t really matter, but an if/else structure will only allow the first instance of true to be executed whereas multiple if statements are treated separately. The following illustrates the point more effectively:
```
int x = 50;

if (x > 30) {
  println("A");
} else if (x > 20) {
  println("B");
}

if (x > 30) {
  println("C");
}

if (x > 20) {
  println("D"); 
}
```