Introduction to Computer Science – Chapter 8

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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

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### 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
• 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;’