In this lab you will work through a set of problems involving python objects and classes.

The initial setup involves copying five programs and three image files from the instructor's account to your own, and making each of the programs executable.

Once that is complete, you will be conducting several experiments with the programs and writing a short analysis explaining their behaviour. (All the details are provided below.)

Initial setup

   cd games
   mkdir lab6
   cd lab6

Run the ls command and check to see that all eight files are present in your current directory.

Run the chmod command to make the programs executable:
chmod u+x *.py

This completes the setup, you can now proceed to the three key parts of the lab below

Part 1: functions

Your objective for this part of the exercise is to run the two programs, write the output each produces in the table below, and then explain why they differ the way they do based on the code and the output.

#! /usr/bin/python

print "progress check A"

lives = 3
while (lives > 0):
   print "lives left: ", lives
   lives = lives - 1

print "progress check B"

#! /usr/bin/python

print "progress check A"

def mainGame(numLives):
   lives = numLives
   while (lives > 0):
      print "lives left: ", lives
      lives = lives - 1

print "progress check B"

mainGame(4)

print "progress check C"

mainGame(2)

print "progress check D"

Output from part1a.py

Output from part1b.py

Explanation of the difference in output between 1a and 1b

Part 2: Objects

Your objective for this part of the exercise is to run the two programs, write the output each produces in the table below, and then explain what advantages, from a coding perspective, part b might have over part a.

part2a.py	part2b.py
#! /usr/bin/python # create two critters, specify their name and age bobsName = 'Bob' bobsAge = 5 philsName = 'Phil' philsAge = 1 # run the update routine on each once every 'year' year = 1 while (year <= 3): print "It is year", year bobsAge = bobsAge + 1 philsAge = philsAge + 1 print bobsName, "is now", bobsAge print philsName, "is now", philsAge year = year + 1	#! /usr/bin/python class Critter: # this routine gets run automatically # when a Critter is first created def __init__(self, age, name): # store the critter's name and age self.myAge = age self.myName = name # this routine ages the critter by a year def update(self): self.myAge = self.myAge + 1 print self.myName, "is now", self.myAge # create a couple of Critters using the class bob = Critter(5, 'Bob') # bob starts off at age 5 phil = Critter(1, 'Phil') # phil starts off at age 1 # run the update routine on each once every 'year' year = 1 while (year <= 3): print "It is year", year bob.update() phil.update() year = year + 1
Output from part2a.py	Output from part2b.py
Possible coding advantages of 2b over 2a

Part 3: Objects (part 2)

1. Use functions to group different logical portions of the game control, and

2. use classes to control the behaviour of the moving objects (i.e. the star and the ship) in the game

Your objectives for this part of the exercise are to:

1. Run the program and describe how the ship and star are controlled (i.e. the effect of the various keypresses and mouseclicks).

2. Describe in detail the sequence of routines that get called during a typical pass through the "while keepPlaying" loop of the mainGame() function. (For simplicity, you can assume that no collisions or wrap-arounds take place during this pass.)

part3.py code

#! /usr/bin/python # --------------------------------------------------------------------- # **** LIBRARY SELECTION AND GLOBAL VARIABLE SETUP **** # --------------------------------------------------------------------- # import and initialize the pygame module import pygame # set up default values for the screen sizes # (these can be overriden by the setup_pygame function) screenSize = screenWidth,screenHeight = 480,320 # set up a default display and background image for the game gameDisplay = None background = None # --------------------------------------------------------------------- # **** PYGAME/DISPLAY SETUP ROUTINE **** # --------------------------------------------------------------------- def setup_pygame(width, height): # make sure we use the global (shared) versions # of the various screen size variables global screenSize, screenWidth, screenHeight global gameDisplay, background # initialize pygame and the display values pygame.init() screenSize = screenWidth,screenHeight = width,height gameDisplay = pygame.display.set_mode(screenSize) # load the background image background = pygame.image.load("backdrop.gif") # --------------------------------------------------------------------- # **** CLASS TO DEFINE AND CONTROL OBJECTS THAT MOVE IN THE GAME **** # --------------------------------------------------------------------- class movingItem: def __init__(self, imageFile, (x,y)): # load the original image from a file self.Original = pygame.image.load(imageFile) # set up the initial facing of the item and rotate # its image to face that direction self.Facing = 0 self.Image = pygame.transform.rotate(self.Original, self.Facing) # set up a box (rectangle) around the item self.Box = self.Image.get_rect() # set up the initial coordinates for the item self.Box.x = x self.Box.y = y # set the speed so the item is initially stationary self.Speed = [0,0] def update(self): # adjust the object's position based on its current speed self.Box = self.Box.move(self.Speed) # have the object 'wrap around' if it goes off the screen if self.Box.left > screenWidth: self.Box.right = 1 elif self.Box.right < 0: self.Box.left = screenWidth - 1 if self.Box.bottom < 0: self.Box.top = screenHeight - 1 elif self.Box.top > screenHeight: self.Box.bottom = 1 # rotate the object appropriately for its current facing self.Image = pygame.transform.rotate(self.Original, self.Facing) # --------------------------------------------------------------------- # **** COLLISION HANDLING ROUTINE FOR THE GAME **** # --------------------------------------------------------------------- # this routine handles collisions between two movingItem objects def handleCollision(item1, item2): red = 255,0,0 if (item1.Box.colliderect(item2.Box)): pygame.draw.line(gameDisplay, red, (0, 0), (screenWidth, screenHeight), 5) pygame.draw.line(gameDisplay, red, (0, screenHeight), (screenWidth, 0), 5) pygame.display.flip() pygame.time.delay(1000) # --------------------------------------------------------------------- # **** DISPLAY UPDATING ROUTINE FOR THE GAME **** # --------------------------------------------------------------------- # this routine handles updating and redrawing the display, # assuming it is given the background image and a list # of movingItems to update def updateDisplay(bck, itemList): # remember to look up the global display variable global gameDisplay # redraw the background picture to the screen buffer gameDisplay.blit(background, (0,0)) # redraw the items in the order they appear in the list for i in itemList: gameDisplay.blit(i.Image, i.Box) # update the visible display from the screen buffer pygame.display.flip() # --------------------------------------------------------------------- # **** EVENT PROCESSING ROUTINE FOR THE GAME **** # --------------------------------------------------------------------- # this routine handles all event processing for the game # it assumes it is given two movingItems to manipulate, # the first one jumps when the player clicks on the display, # the second one's speed is controlled by the arrow keys def handleEvents(jumpingItem, travelingItem): # check for all events that have taken place during # this turn (keypresses, mouseclicks, etc) # and process them one at a time for event in pygame.event.get(): # check to see if the player clicked the window close box if event.type == pygame.QUIT: keepPlaying = False print "Player command: close window" # if the player clicked on the screen # have the star "jump" to the new location if event.type == pygame.MOUSEBUTTONDOWN: jumpingItem.Box.center = event.pos # check to see if the player pressed any keys if event.type == pygame.KEYDOWN: # treat the Q key as a quit command if event.key == pygame.K_q: print "Player command: quit (q)" return False elif event.key == pygame.K_UP: travelingItem.Speed = [0, -4] travelingItem.Facing = 45 elif event.key == pygame.K_DOWN: travelingItem.Speed = [0, 4] travelingItem.Facing = 225 elif event.key == pygame.K_LEFT: travelingItem.Speed = [-4, 0] travelingItem.Facing = 135 elif event.key == pygame.K_RIGHT: travelingItem.Speed = [4, 0] travelingItem.Facing = 315 # end of the events for loop # none of the events said to quit, so return True return True # --------------------------------------------------------------------- # **** MAIN CONTROL/PROCESSING ROUTINE FOR THE GAME **** # --------------------------------------------------------------------- # this routine controls the operational portion of the game, # assuming the pygame setup routine has already been run def mainGame(): # create the moving star and ship star = movingItem('star.gif', (100,100)) ship = movingItem('ship.gif', (200,200)) # run the game loop keepPlaying = True numCollisions = 0 while keepPlaying: # update the facing, speed, and position of # the star and the ship ship.update() star.update() # check for collisions between the star and the ship handleCollision(star, ship) # redraw the display updateDisplay(background, [star, ship]) # pause for 20 milliseconds before continuing pygame.time.delay(30) # handle any pending events keepPlaying = handleEvents(star, ship) # end of the keepPlaying while loop # --------------------------------------------------------------------- # **** RUN THE SETUP AND MAIN GAME ROUTINES *** # --------------------------------------------------------------------- setup_pygame(640,480) mainGame() print "shutting down the game" # --------------------------------------------------------------------- # **** END OF PROGRAM **** # ---------------------------------------------------------------------

Description of ship/star control and behaviour

Explanation of the event sequence