Learning Processing: Chapter 6: Example 6-9: Simple While Loop with Interactivity

Example

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

// Example 6-9: Simple while loop with interactivity

void setup() {
  size(255,255);
}

void draw() {
  background(0);

  // Start with i as 0
  int i = 0;

  // While i is less than the width of the window
  while (i < width) {
    noStroke();
    // The distance between the current rectangle and the mouse is equal to the absolute value of the difference between i and mouseX.
    float distance = abs(mouseX - i); 
    // That distance is used to fill the color of a rectangle at horizontal location i.
    fill(distance);
    rect(i,0,10,height);
    // Increase i by 10
    i += 10;
  }
}

Comments (3)

michel

Hi.
I’m really enjoying this book and have been able to follow the course so far.
Now I’m having some troubles understanding this chapter.

1: In exercise 6-4 I don’t understand why the outcome of #2: \Local count\
is zero and not 100 as #1.

2: I just can’t figure out this example. I manage to do the exercise, to rewrite the example with a for loop instead of a while loop but I still doesn’t understand how it works.
I would really appreciate an explanation of each step. What is happening to fill etc…

thanks for a fantastic book!

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

1) Because “count” is declared in draw(), it is reset to 0 every time draw executes, and therefore can never be any other value than 0.

2) Check out figure 6-7 for the exact inner workings of a “for” loop.

Good luck!
michel

Thank you Daniel!

#2 in my question referred to example 6-9 here above but I just managed to figure it out by recreating each step in the loop on paper after your suggestion.

Michel