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Let's take the Example 1 and expand it to use events:

int length1 = 0;
int length2 = 0;

void setup() {
  size(300, 300); // define window size
  smoothbackground(0); // define background colour
  stroke(255, 255, 255); }
 // define line colour
}
void draw() {
  background(0);
  length1  strokeWeight(1)= mouseX;
  length2 = mouseY;
  line(100, 10, 100,150 length1); // draw a line
  line(150, 10, 150,200 length2);
  line(200, 10, 200, 250);


  fill(0, 0, 0); // fill colour
  strokeWeight(5); // line thickness
  ellipse(100,150 length1, 50, 50); // draw an ellipse
  ellipse(150,200 length2, 50, 50); // draw an ellipse
  noFill(); // turn off fill
  ellipse(200, 250, 50, 50); // draw an ellipse
}

In this program we use two special functions:

• void setup ()
• void draw ()

These functions accept no parameters so the space between the brackets is left blank, and they have no return value so the 'void' keyword is used . The function names are reserved names that Processing knows, Processing calls these (this will make more sense when we look at writing our functions). Processing calls the setup functions as soon as the corresponding event occurs.program starts, and the draw function every time the screen refreshes. We will use these two functions for all of our future processing sketches.  

Exercise 3:

Take your results to form exercise 2, and modify it so it animates across the screen. 

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