Chapter 3: Exercise 3-7: Continous Line with Varying Thickness

The formula for calculating the speed of the mouse’s horizontal motion is the absolute value of the difference between mouseX and pmouseX. The absolute value of a number is defined as that number without its sign:

• The absolute value of –2 is 2.
• The absolute value of 2 is 2.

In Processing, we can get the absolute value of the number by placing it inside the abs() function. The speed at which the mouse is moving is therefore:

• abs(mouseX - pmouseX)

Update Example 3-4 so that the faster the user moves the mouse, the wider the drawn line.

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

void setup() {
  size(200, 200);
  background(255);
  smooth();
}

void draw() {
  stroke(0);
  strokeWeight(abs(pmouseX - mouseX));
  line(pmouseX, pmouseY, mouseX, mouseY);
}