Introduction to Computer Science – Chapter 8 CSc 2010 Spring 2011 Marco 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(). ( ) 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.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(, ) ▫mytext = Text(Point(50,50), ‘hello world’) ▫mytext.draw(myCanvas) We can also display images ▫myphoto = Image(, )

Sound We have used the beep command ▫beep(, ) We can make our computer beep as well ▫computer.beep(, ) 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 ( ) ▫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( ) ▫Reads a file and returns a song object playSong( ) ▫Plays the given song makeSong( ) ▫Returns a song object based on the string of notes given