CSC111 Lab 12 2011

--D. Thiebaut 09:42, 30 November 2011 (EST)

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This lab will have you play with classes and objects: the essence of Object Oriented Programming!

Part 1: A Bus

• Using the example we did in class on Tuesday as inspiration (see similar code below), create a new program that draws the bus shown above.
• Your program should have two classes:
  • class Wheel
  • class Bus

# A program with a car and a wheel class.
# This is slightly different from what we did in class, but works
# the same.  Figure out what the differences are.
#
from graphics import *
W = 800
H = 600
 
#----------------------------------------------------------------
class Wheel:
    """A class with two concentric circles"""
 
    def __init__( self, center, r1, r2 ):
        self.circ1 = Circle( center, r1 )
        self.circ2 = Circle( center, r2 )
        r1, r2 = min( r1, r2 ), max( r1, r2 )
        self.radius1 = r1
        self.radius2 = r2
 
    def draw( self, win ):
        """draws the wheel on the window"""
        self.circ2.draw( win )
        self.circ1.draw( win )
 
    def setFill( self, color1, color2 ):
        """colors the outside and inside circles.  First color for small circle"""
        self.circ1.setFill( color1 )
        self.circ2.setFill( color2 )
 
    def getRadius1( self ):
        """returns radius of small circle"""
        return self.radius1
 
    def getRadius2( self ):
        """returns radius of large circle"""
        return self.radius2
 
#----------------------------------------------------------------
class Car:
    """A class for a car, which is a rectangle and two wheels"""

    def __init__( self, P1, P2 ):
        """Get 2 points and create the box and two wheels from the dimensions"""
        self.P1 = P1
        self.P2 = P2
        self.width = abs( P1.getX()-P2.getX() )
        self.height= abs( P1.getY()-P2.getY() )
 
        self.rect    = Rectangle( P1, P2 )
        center1      = Point( P1.getX()+self.width/8, P2.getY() )
        center2      = Point( P1.getX()+self.width*7/8, P2.getY() )
        radius2      = self.height/3
        radius1      = radius2/2
        self.wheel1  = Wheel( center1, radius1, radius2 )
        self.wheel2  = Wheel( center2, radius1, radius2 )
 
    def draw( self, win ):
        """draws the car on the screen.  One of the wheels is covered"""
        self.wheel2.draw( win )
        self.rect.draw( win )
        self.wheel1.draw( win )

    def move( self, dx, dy ):
        """moves the car by dx and dy"""
        self.wheel2.move( dx, dy )
        self.rect.move( dx, dy )
        self.wheel1.move( dx, dy ) 
 
#----------------------------------------------------------------
def waitForClick( win, message ):
    """ waitForClick: stops the GUI and displays a message.  
    Returns when the user clicks the window. The message is erased."""
 
    # wait for user to click mouse to start
    startMsg = Text( Point( win.getWidth()/2, win.getHeight()/2 ), message )
    startMsg.draw( win )    # display message
    win.getMouse()          # wait
    startMsg.undraw()       # erase
 
 
def main():
    global W, H
    win = GraphWin( "wheel demo", W, H )
 
    waitForClick( win, "click to start" )
    car = Car( Point( 100,100 ), Point( 250, 170 ) )
 
    car.draw( win )
    waitForClick( win, "click to end" )
 
main()

Challenge 1

• Add a for-loop that makes your bus disappear from the window. Make it go in the forward direction (i.e. left for the bus in the image above).

class Tree:
 
    def __init__( ... ):
        ...

    def draw( ... ):
        ...

    def move( ... ):
        ...

• Make your program display the tree with the bus. No need for any of them to move, but that's fine if the bus is moving out of the window...

Part 2: Trees

• Create a new class in your program called Tree. It will represent a simplified tree, with its green head of leaves, and its brown trunk.
• Make your program display the bus and the tree. It doesn't matter if the tree is in front or behind the bus.

Challenge 2

• Make the bus stand still and the tree move in the direction opposite of the bus direction.
• Make the tree move out of the window

Challenge 3

• Add another tree object. One class: two objects.
• Locate the trees in different locations so that they do not overlap (hint: you can change the constructor so that you can specify the x-coordinate of the tree object when you create it:)
• Make your program display the two trees and the bus

Challenge 4

• Make the two trees move to the right and disappear from the window

Challenge 5

• Make the trees that disappear from the right reappear on the left, giving the illusion of a real cartoon!
• For this your program will have to ask the tree object to return its x position, and if this position is larger than the width plus some offset, then the tree will have to move by a large negative dx value...

     class Tree:
         ...
         def getX( ... ):
              return ...


     def main():
         ...

         if tree.getX() > width:
              tree.move( -nnnn, 0 )