Introduction to Computer Science – Chapter 8CSc 2010Spring 2011Marco Valero

Overview

• Drawing a canvas

• Objects and constructors

• Animation

• Scope

• Text and images

• Sound

• Scales and making music

• Songs

Drawing a canvas

• We’ve seen the canvas before

▫Asking a question

▫Showing a picture

• myCanvas = GraphWin()

▫myCanvas.close()

▫myCanvas.setBackground(‘white’)

• myCanvas = GraphWin(‘My Masterpiece’, 200,

300)

Drawing a canvas

•Uses a grid layout of coordinates for position

▫(0,0) is the top left corner

•We can create points and lines

▫p = Point(100, 50)

▫p.draw(myCanvas)

▫l = Line(Point(0,0), Point(100, 200))

▫l.draw(myCanvas)

Objects and constructors

• We’ve seen this style of functions before

▫ myList.append(‘a’)

▫ myList.sort()

• <object>.<function identifier>(<parameters>)

• Think of variables as an object that encapsulates some

data and functionality

• We construct these objects with special functions called

constructors

▫ p = Point(100, 50)

Objects and constructors

• Objects may have many member functions

• p = Point(100, 50)

• p.getX() returns 100

• p.getY() returns 50

• l = Line(p, Point(75,200))

• l.getP1().getX() returns?

• L.getP2().getX() returns?

Animation

• <graphic object>.undraw()

▫Erases object from the screen

• Circles are defined as a point with a radius

▫c = Circle(Point(100, 50), 30)

▫c.draw(myCanvas)

• By using the undraw and draw methods we

can animate our graphics

Scope

• Scope is the ability to ‘see’ or ‘know of’ an

identifier in python

• Scope of an identifier in python is in ‘textual

order’, and local to functions

• A global defined at the top will be visible to all

• A variable within a function will only be

visible to that specific function’s body

Text and images

•We can create graphic representations of

text

•myText = Text(<anchor point>, <string>)

▫mytext = Text(Point(50,50), ‘hello world’)

▫mytext.draw(myCanvas)

•We can also display images

▫myphoto = Image(<center point>, <file

name>)

Sound

•We have used the beep command

▫beep(<seconds>, <frequency>)

•We can make our computer beep as well

▫computer.beep(<seconds>, <frequency>)

•Sorry, no wobble bass electro music

Scales and making music

•A scale is 12 notes▫C C#/Db D D#/Eb E F F#/Gb G G#/Ab A

A#/Bb B▫Also known as an octave

•We can double an octave by doubling the frequency▫C3 (130.815)▫C4 (261.63)

•The lowest scribbler can go is A0(27.5 Hz)

Songs• We can create a string of notes and durations

for myro to play as a song▫Note1 [Note2] Fraction of a Whole Note▫ ‘C5 1;’

• readSong(<file name>)▫Reads a file and returns a song object

• playSong(<song>)▫Plays the given song

• makeSong(<textual song>)▫Returns a song object based on the string of

notes given