deutsche Version

Functions are an elementary part of programming languages. With them programs can be simplified and presented in a manageable and reusable way (modularisation). Functions also help us to keep our code organised and understandable. 

Functions act as jumps in the program. In the event of a function call, the program jumps to the position where the function is defined and then returns after the function has been executed. Most programming languages have many built in or native functions. To find out how the functions work, and what parameters they expect, we need to look at the processing documentation (https://processing.org/reference/).

In the previous examples we have written programs without functions. These programs were not interactive and do not include animations. So how can you extend a program so that, for example, the keyboard is used as an input? The answer is to use program events, which are recorded and forwarded by the program. Here is a short list of some such events:

• program start
• refresh of the window
• keyboard input
• mouse input

These events can be intercepted. To do this, we only need to write functions (with names defined by processing) that are called automatically for the respective events.

• setup ->  Programme start
• draw -> Refresh of the output window
• keyPressed -> keyboard press
• mousePressed -> Mouse button press

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

void setup()
{
  size(300,300);
  smooth();
  stroke(255,255,255);
}
 
void draw()
{
  background(0);
 
  strokeWeight(1);
  line(100,10,100,150);
  line(150,10,150,200);
  line(200,10,200,250);
 
  fill(0,0,0);
  strokeWeight(5);
  ellipse(100,150,50,50);
  ellipse(150,200,50,50);
  noFill();
  ellipse(200,250,50,50);
}

In this program we use two 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 functions as soon as the corresponding event occurs.

Exercise 3:

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