Intro to Robots

8 Sights & Sounds

Intro to Robots

Computing is more than Computation

• So many devices – iPod, digital cameras, etc – use computers to do so much more than “compute”.

• Such devices manage and manipulate images and sounds in amazing ways.

• In this chapter we try to get some of that for ourselves.

Intro to Robots

GraphWin():

• Myro comes with a graphics windows in which we can play.

• We create it by invoking it by name:

• This produces a gray 200 x 200 pixel window.

• The myCanvas window becomesour canvas where we exploringdrawing images.

From myro import *

myCanvas = GraphWin()

Exercise: Are pixels round, square orrectangular?

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GraphWin():

• Close it

• And create it again with a new name and size.

• Change its color

myCanvas.close()

myCanvas = GraphWin(‘Silly Scene’,200,300)

myCanvas.setBackground(“white”)

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Moment of Reflection:

• Our graphics window is an “object” with a name – myCanvas.

• You can create an object by calling a function whose name identifies the “type” of object (also called its class).

• We communicate with our window by “sending it messages”

myCanvas.setBackground(“white”)

message name

name of message “receiver”

message argument

myCanvas = GraphWin(‘Silly Scene’,200,300)

Intro to Robots

Locating the Pixels

• Pixels, like points on the xy-plane, have coordinates.• The coordinate numbering system begins in the top, left-

hand corner.

(0,0)

(100,100)

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Creating More Objects

• Besides graphics windows objects we can create many others – points, lines, circles, etc.

• Up to this point, p only exists in the programming interface (IDLE). To see it, we need to place it on the graphics window at its specified location.

• Remember, we are sending a message to p to draw itself on the myCanvas graphics window.

p = Point(100,125)

p.draw(myCanvas)

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Point object messages:

• There are some more messages we can send to a Point.

getX() # returns the x-coordinategetY() # returns the y-coordinateundraw() # makes the object disappear

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What’s the Point?

• Points by themselves are not so interesting. • What is really the point is that with them we can draw

lines.• There is a lab exercise where we end up drawing a line

by ourselves.• Alternatively we can create a Line object.• A Line object is a straight line between two end points.

myLine = Line(Point(5,100), Point(50,200))

executing the Line function creates a new Line object

the arguments of the Line function are its starting andending Points. These pointsare created by calling the Point()function twice.myLine.draw()

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A real Fan of Lines.

for n in range(0, 200, 5): L=Line(Point(n,25),Point(100,100)) L.draw(myCanvas)

range(x,y,z) is a function thatreturns a list of numbers startingat x, x+z, x+2z, … until y

all the lines drawn have a commonend-point – Point(100,100)

all the lines drawn have starting pointswith a common y-coordinate (25)

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Other Line functions:

L = Line(Point(25,25), Point(100,100))L.draw()

start = L.getP1() # returns the starting point of lineend = L.getP2() # returns the end point of line

print start.getX(), start.getY(), end.getX(), end.getY()25 25 100 100

L.undraw()

Exercise: If L is a line, print out the starting and ending coordinates of L as (x,y)

print ‘(‘,L.getP1().getX(),’,’,L.getP1().getY(),’)’print ‘(‘,L.getP2().getX(),’,’,L.getP2().getY(),’)’

We send L a message to return its starting point and the startingpoint a message to return its x-coordinate. Obviously, the dot (.) operatorfunctions like +, left-to-right.

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Circles:

• The definition of a circle is “the set of points equidistant from a given point”.

• The Circle object has a similar definition.

myCircle = Circle(Point(100,100), 50)myCircle.draw()

center point radius

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Circle Functions:

• You can change and retrieve various Circle characteristics.

c = Circle(Point(100, 150), 30)c.draw(myCanvas)centerPoint = c.getCenter()

c.setOutline(“red”) # line colorc.setFill(“yellow”) # interior fill colorc.setWidth(5) # line width in pixels

color = color_rgb(100,125,150)c.setFill(color)

Exercise: Try out these commands

Intro to Robots

Circle Example

# Program to draw a bunch of # random colored circlesfrom myro import *from random import *

width = 500height = 500

def makeCircle(x, y, r): # creates a Circle centered at point (x, y) of radius r # we plan to use randomly generated numbers x, y and r return Circle(Point(x, y), r)

def makeColor(): # creates a new color using random RGB values red = randrange(0, 256) # returns a random number between 0 and 255 green = randrange(0, 256) # returns a random number between 0 and 255 blue = randrange(0, 256) # returns a random number between 0 and 255 return color_rgb(red, green,blue)

main()

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Circle Example def main(): # Create and display a graphics window myCanvas = GraphWin("Cicrles", width, height) myCanvas.setBackground("white") # draw a bunch of random circles with random colors. N = 500 for i in range(N): # pick random center # point and radius # in the window x = randrange(0,width) y = randrange(0,height) r = randrange(5, 25) c = makeCircle(x, y, r) # select a random color c.setFill(makeColor()) c.draw(myCanvas)

Intro to Robots

Function Definition Alternatives:

• Consider the following two examples:

• makeCircle() hides the details of makeCircle(x,y,r) exposes by requiring previously assigned values for x, y and r

x = randrange(0,width)y = randrange(0,height)r = randrange(5, 25)c = makeCircle(x, y, r)

def makeCircle():# creates a Circle centered at point (x, y) of radius rx = randrange(0,width) # only if width is “global”y = randrange(0,height) # only if height is “global”r = randrange(5, 25)return Circle(Point(x, y), r)

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Variable Scope:

• Variables defined outside any function definition have “global” scope. They can be used anywhere in the program.

• Variables defined inside a function have scope restricted to that function. If you want to use their values in a different functions you need to pass them as arguments.

def foo(): x = 4 # scope of x is inside foo() y = 5 # scope of y is inside foo() return bar()

def bar(): z = x + y # fails because x and y are # have scope within foo() only return z

def foo(): x = 4 y = 5 # now pass x and y as arguments return bar(x,y)

def bar(a,b): z = a + b return z

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Pros and Cons

• Having global variables is nice because you can use them whenever you need them.

• However it gives you added responsibility not to misuse the variable (change its value by mistake, for example)

• A variable with a function scope can only be modified inside that function.

Intro to Robots

Sound:

• Both the computer and the robot can beep().

• What is Hertz?

beep(1,440) # plays a 440 Hz tone for 1 secondcomputer.beep(1,440) # computer plays the same tone

Hertz is the unit for measuring frequencies 1 Hz = 1 cycle/second

1 cycle

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Sound (cont):

• Computer CPUs measure their “speed” in Gigahertz.

• Computer CPUs have an internal clock that “ticks” at the Gigahertz rate of the CPU.

• All the various components of a computer synchronize their activities against this clock.

1 Gigahertz = 109 cycles / second

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Sound (cont):

• Other periodic motions:

• What is sound?

• What can the human ear hear?

earth rotational rate: 1/day = 1/86400 seconds = 0.00001157 cycles/second

cd rotational rate: 400 turns/second52x cd rotational rate: 52*400/second = 20800/second

hummingbird wing flap rate: 20-78 flaps/second

A periodic compression and decompression (refraction) of air. 1 cycle of sound = 1 compression + 1 decompression

440 cycles/second = 440 compressions and decompressions / second

in the range 20Hz to 20000Hz (20KHz)

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What sounds can Scribbler make?

• A musical scale consists of 12 sounds

• You can move up or down an octave by multiplying or dividing by 2.

• The C-note in various octaves is identified as:

C C#/Db D D#/Eb E F F#/Gb G G#/Ab A A#/Bb B

C0 C1 C2 C3 C4 C5 C6 C7 C8

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Music:

• C4 has frequency 261.63 Hz. Try it out with Scribbler.• The notes in a scale are exponentially equidistant. By

this we mean:

C4 frequency = 261.63 * 2(0/12) Hz = 261.63 * 20 Hz = 261.63 HzC#4 frequency = 261.63 * 2(1/12) Hz = 261.63 * 20.08333 Hz = 277.19 Hz D4 frequency = 261.63 * 2(2/12) Hz = 261.63 * 20.16666 Hz = 293.67 HzD#4 frequency = 261.63 * 2(3/12) Hz = 261.63 * 20.25000 Hz = 311.13 Hz E4 frequency = 261.63 * 2(4/12) Hz = 261.63 * 20.33333 Hz = 329.63 Hz F4 frequency = 261.63 * 2(5/12) Hz = 261.63 * 20.41666 Hz = 349.23 Hz F#4 frequency = 261.63 * 2(6/12) Hz = 261.63 * 20.50000 Hz = 370.00 Hz G4 frequency = 261.63 * 2(7/12) Hz = 261.63 * 20.58333 Hz = 392.00 Hz G#4 frequency = 261.63 * 2(8/12) Hz = 261.63 * 20.66666 Hz = 415.31 Hz A4 frequency = 261.63 * 2(9/12) Hz = 261.63 * 20.75000 Hz = 440.01 Hz A#4 frequency = 261.63 * 2(10/12) Hz = 261.63 * 20.83333 Hz = 466.17 Hz B4 frequency = 261.63 * 2(11/12) Hz = 261.63 * 20.91666 Hz = 493.89 HzC5 frequency = 261.63 * 2(12/12) Hz = 261.63 * 21 Hz = 523.26 Hz

Intro to Robots

Music Tempo:

• Music has tempo. In tempo– a quarter note is 0.68 seconds– A half note is 1.36 seconds– A whole note is 2.72 seconds.

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Intro to Robots

Myro Music:

• Playing notes by frequency and time is a pain.• Myro lets you “write out a tune” as a string and then

converts the string into a song.

• Each note in the string is either

or

where note = ‘C4’, etc and time = ¼, ½, 1, etc

tune = “c 1; d 1; e 1; f 1; g 1; a 1; b 1; c7 1;“song = makeSong(tune)computer.playSong(song)

note time;

note1 note2 time;

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Myro Music 2:

• You can also put your string in a file and myro will read the file and play the song.

• Of course, if you want, the robot can play the song itself, just drop the “computer” receiver tag.

song = readSong(filename)computer.playSong(song)

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Myro Reference:

• The end of chapter 8 holds a review of the myro graphics function calls.

GraphWin()GraphWin(<title>, <width>, <height>)<window>.close()<window>.setBackground(<color>)

<new_color> = color_rgb(<red>, <green>, <blue>)

Point(<x>, <y>)<point>.getX()<point>.getY()

Line(<start point>, <end point>)

Circle(<center point>, <radius>)

Rectangle(<point1>, <point2>)

Oval(<point1>, <point2>)

Polygon(<point1>, <point2>, <point3>,…)Polygon([<point1>, <point2>, …])

Text(<anchor point>, <string>)

Image(<centerPoint>, <file name>)

<object>.draw(<window>)<object>.undraw()<object>.getCenter()<object>.setOutline(<color>)<object>.setFill(<color>)<object>.setWidth(<pixels>)<object>.move(<dx>, <dy>)

Intro to Robots

Myro Reference:

• The end of chapter 8 holds a review of the myro graphics function calls.

beep(<seconds>, <frequency>)beep(<seconds>, <f1>, <f2>)

<robot/computer object>.beep(<seconds>, <frequency>)<robot/computer object>.beep(<seconds>, <f1>, <f2>)

robot.playSong(<song>)readSong(<filename>)song2text(song)makeSong(<text>)text2song(<text>)