PyGame for Game Development: Sprite Groups and Collision Detection (Page 1 of 4 )
In this second part of a tutorial covering PyGame, you will learn how to manage entire groups of sprites. You'll also learn how to test for collisions within your applications.
Sprite Groups
While managing sprites individually may be ideal for small applications, think about managing dozens of sprites in more complex applications. Obviously, there has to be a way to efficiently manage all of them, and sprite groups do just that. The definition of a sprite group is pretty simple and true to the term. Sprite groups are simply groups of sprites that are related in some way. Sprites can also belong to multiple groups, rather than just being limited to one group. Besides providing a convenient way to iterate over related sprites, some sprite groups contain special features to aid with development, which we'll take a look at later. First, though, let's put together a simple program that uses a sprite group to move three stick men up and down the screen.
We'll start with the most basic sprite group, the Group class:
import pygame
import sys
class StickMan(pygame.sprite.Sprite):
# We'll just accept the x-position here
def __init__(self, xPosition):
pygame.sprite.Sprite.__init__(self)
self.old = (0, 0, 0, 0)
self.image = pygame.image.load('stickMan.gif')
self.rect = self.image.get_rect()
self.rect.x = xPosition
# The x-position remains the same
def update(self, yPosition):
self.old = self.rect
self.rect = self.rect.move([0, yPosition - self.rect.y])
# Define a function to erase old sprite positions
# This will be used later
def eraseSprite(screen, rect):
screen.blit(blank, rect)
pygame.init()
screen = pygame.display.set_mode((256, 256))
pygame.display.set_caption('Sprite Groups')
screen.fill((255, 255, 255))
# Create the three stick men
stick1 = StickMan(25)
stick2 = StickMan(75)
stick3 = StickMan(125)
# Create a group and add the sprites
stickGroup = pygame.sprite.Group()
stickGroup.add((stick1, stick2, stick3))
# Add a variable for the direction, y-position and height of the
sprite we are dealing with
stickGroup.direction = "up"
stickGroup.y = screen.get_rect().centery
stickGroup.height = stick1.rect.height
# Create a blank piece of background
blank = pygame.Surface((stick1.rect.width, stick1.rect.height))
blank.fill((255, 255, 255))
pygame.display.update()
# Create an event that will appear ever 100 milliseconds
# This will be used to update the screen
pygame.time.set_timer(pygame.USEREVENT + 1, 100)
while True:
for event in pygame.event.get():
if event.type == pygame.QUIT:
sys.exit()
# Check for our update event
if event.type == pygame.USEREVENT + 1:
# Update the y-position
if stickGroup.direction == "up":
stickGroup.y = stickGroup.y - 10
else:
stickGroup.y = stickGroup.y + 10
# Check if we have gone off the screen
# If we have, fix it
if stickGroup.direction == "up" and stickGroup.y <= 0:
stickGroup.direction = "down"
elif stickGroup.direction == "down" and stickGroup.y >=
(screen.get_rect().height - stickGroup.height):
stickGroup.direction = "up"
stickGroup.y = screen.get_rect().height -
stickGroup.height
# Clear the old sprites
# Notice that we pass our eraseSprite function
# This will be called, and the screen and old position
will be passed
stickGroup.clear(screen, eraseSprite)
# Update the sprites
stickGroup.update(stickGroup.y)
# Blit the sprites
stickGroup.draw(screen)
# Create a list to store the updated rectangles
updateRects = []
# Get the updated rectangles
for man in stickGroup:
updateRects.append(man.old)
updateRects.append(man.rect)
pygame.display.update(updateRects)
Next: Explaining the Group Class >>
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