Review

• Identifiers, Variables
• Types, Type Conversion
• Operators, Expressions
• Modules
• Problem Solving with Variables and Expressions

Anatomy of a Function

Custom Functions

• Named, reusable packages of code
• Useful for organizing and abstracting software
• Can be defined to take 0 or more arguments
• Can return values to function caller

Custom Function Syntax

def funcName( arg1, arg2, arg3 ): # Header
    statement1                    # Body
    statement2
    statement3

• 'def' keyword
• arguments
• colon at end of function header
• whitespace!
• Note how the statments in the body are indented to the same extent.
• Very important!

Custom Functions - Example

# Draw an eyeball at position x, y
def eyeball(x, y):
    stroke(0)
    fill(255)
    ellipse(x, y, 50, 40)  # Sclera
    fill(0, 255, 0)
    ellipse(x, y, 25, 25)  # Iris
    fill(0)
    ellipse(x, y, 10, 10)  # Pupil

Custom Functions - Example

from Processing import *
window(350, 300)

# Draw an eyeball at position x, y
def eyeball(x, y):
    stroke(0)
    fill(255)
    ellipse(x, y, 50, 40)  # Sclera
    fill(0, 255, 0)
    ellipse(x, y, 25, 25)  # Iris
    fill(0)
    ellipse(x, y, 10, 10)  # Pupil

eyeball(100, 100)
eyeball(250, 100)

Custom Functions

Note: Values passed to the eyeball() function are copied into local arguments x and y The function must be declared *before* it is used When the function is called, the calling statement waits until the function completes

Function Return Values

• Functions accept values as arguments (between parens - values in)
• They return values using the return keyword (values out)
• Function execution stops when the return statement is executed
• Upon executing the return statement, the returned value takes the place of the function call
• Execution picks up where left off

Function Return Values - Example

def square(x):
    y = x * x
    return y

toSquare = 10
result = square(toSquare)
print("The result of ", toSquare, " squared is ", result)

Function Return Values - None

If a function has no return statement, it returns None when complete

• None is a special keyword meaning the absense of a value

What does eyeball() return?

rv = eyeball(100, 100)
print( rv )     # rv has the value None 

Event-driven Programming

• Flow of control is determined by "events":
  ... mouse clicks, mouse moves, key presses, timer ticks, etc.
• Events allow the user to interact with your program
• A Timer can be used to create animations by repeatedly calling a function on a Tick event
• An event can be handled by a function...
  ... the handling function is called whenever the event is raised

Events in Calico Processing

Handling Events

• Events are handled by functions

  def myFunction(o, e):
      pass                    # pass by, do nothing
  

• Functions are hooked to events using the += operator

  onMousePressed += myFunction

• Functions are unhooked from events usng the -= operators

  onMousePressed -= myFunction

Event Handling Functions

Functions that handle events must take two arguments: object (o), and eventData (e)

# clickEllipse.py
from Processing import *
window(300, 300)

# Draw a randomly colored ellipse
# at the current mouse location
def draw(o, e):
    fill(random(255), random(255), random(255))
    ellipse(mouseX(), mouseY(), 30, 30)

# Hook draw function to the mousepressed event
onMousePressed += draw

Event Handling Functions

Use pmouseX() and pmouseY() to build a drawing program

# draw.py - A simple drawing program
from Processing import *
window(500, 500)

# Draw lines from previous to current mouse
def doDragged(o, e):
    x1 = pmouseX()
    y1 = pmouseY()
    x2 = mouseX()
    y2 = mouseY()
    line(x1, y1, x2, y2)

# Handle mouse dragged
onMouseDragged += doDragged

Calico Processing loop Timer

• An internal loop timer periodically fires an onLoop event.
• The frameRate() function sets the rate at which the event is fired.
• Calling loop() starts the timer.
• Calling noLoop() stops the timer.
• startLoop() and stopLoop() can be used in place of loop() and noLoop()

Simple Animations with the loop Timer

# randomEllipse.py
from Processing import *
window(300, 300)

# Draw ellipses on frame rate
def draw(o, e):
    fill(random(255), random(255), random(255))
    ellipse(mouseX(), mouseY(), 30, 30)

frameRate(10)   # Set loop rate to 10/second
onLoop += draw  # Handle the loop event
loop()          # Start looping

Simple Animations with the loop Timer

# lineRotate.py
from Processing import *
from math import *
window(500, 500)

# Globals and settings
angle, dangle = 0.0, 0.01
strokeWeight(20)
stroke(0, 255, 0)

# Draw the line at the current angle
def rotate(o, e):
    global angle
    background(255)
    x1 = cos(angle)*200+250
    y1 = sin(angle)*200+250
    x2 = cos(angle + PI)*200+250
    y2 = sin(angle + PI)*200+250
    line(x1, y1, x2, y2)
    angle = angle + dangle

# Set up the loop
frameRate(100)
onLoop += rotate
loop()

Events Examples

• clickEllipse.py : Draw an ellipse when the mouse is clicked
• draw.py : A simple drawing program
• randomEllipse.py : Draw an ellipse on a specified interval
• lineRotate.py : A rotating line
• lineRotate2.py : A rotating line with click flip
• drawLines.py : Draw connected lines
• orbitingOrb.py : Draw orbiting orbs