Transcript Session 22 - Computer Science

Computer Science of
Graphics and Games
MONT 105S, Spring 2009
Session 22
Game Graphics
1
Packages
Packages have libraries of Python code that we can use with our
programs.
We will use two packages to create simple games:
•Pygames: The pygames package has many useful classes to
make simple games.
• Livewires: The livewires package was created by educators to
make the pygames package easier to use.
2
Creating a Graphics Screen
We can use the livewires package to create a graphics screen with a background.
Example:
from livewires import games
#import the games package
#Create the graphics screen
games.init(screen_width = 640, screen_height = 480, fps = 50)
#Add a background image to the screen
#First load in an image, then bind it to the background
wall_image = games.load_image("wall.jpg", transparent = False)
games.screen.background = wall_image
#Start the main event loop
games.screen.mainloop( )
3
Adding a sprite
Sprites are images that move around the graphics screen.
To add a sprite, first load in the image, then create a sprite with the image.
Finally, add the sprite to the screen.
Example:
pizza_image = games.load_image("pizza.bmp")
the_pizza = games.Sprite(image = pizza_image, x = 320, y = 240)
games.screen.add(the_pizza)
Note: The coordinate system for the graphics window has (0, 0) at the top left
corner. The y coordinate increases as you move downward in the window.
4
Moving a Sprite
A sprite can be moved by setting the horizontal or vertical displacement
variables (dx and dy) to a non-zero value.
With each iteration of the mainloop( ), the sprite's position by the amount
given by dx and dy.
Example:
the_pizza = games.Sprite(image = pizza_image,
x = 320, y = 240, dx = 1, dy = 1)
This will move the sprite down and to the right.
Note: We can also express the initial position as a function of the screen width
and height:
x = games.screen.width/2, y = games.screen.height/2
The above values will position the sprite in the middle of the screen.
5
Class Inheritance
In python, we can create new classes from existing classes
using inheritance.
The new class inherits everything from the existing class.
We can add new methods and properties, or modify methods
from the existing class.
The new class is called the child or subclass. The existing
class is called the parent or superclass.
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Creating a Pizza class
To generate a more complex motion for our sprite, we will create a
new class that will inherit from the Sprite class.
The new class will define an update function that will move the
pizza in a more complex pattern.
class Pizza(games.Sprite):
"""A bouncing pizza"""
def update(self):
if self.right > games.screen.width or self.left < 0:
self.dx = -self.dx
if self.bottom > games.screen.height or self.top < 0:
self.dy = - self.dy
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