Operation Manual
Experiments in Python
103
Notes:
Adding trees
import random
class worldTreeGroup(pyga me.sprite.Group):
speed = 5
def __init__(self, picture):
pygame.sprite.Group.__init__(self)
treePicture = picture
treeRow = pygame.sprite.Group()
# in rows with a gap somewhere in the middle
# only have a line of trees every 5th row or the
# game is too difcult
for y in range(0, 4 0 0):
if (y % 5 == 0): # every 5th, add tree row with a gap
gapsize = 3 + random.randint(0,6) # size of gap
# starting position of gap
gapstart = random.randint(0,10 - (gapsize//2))
# create a row of 20 trees but 'gapsize'
# skip trees in the middle
for b in range(0, 2 0):
if b >= gapstart and gapsize > 0:
gapsize-=1
else:
new tre e = world Sprit e([b*20, (y+10)*20],
treePicture)
treeRow.add(newtree)
self.ad d(t reeRow)
def update( s e l f ):
for treeRow in s elf:
treeRow.rect.top-=self.speed
if treeRow.rect.top <= -20:
treeRow.kill() # remove this block from ALL groups
Now, if we can get rows of trees advancing on the skier’s position, this game will
be a lot more challenging. Also if the skier hits a tree, the game should stop.
To set up the “piste”, this additional class sets up rows of trees that have a gap in
the middle for the skier to pass through. The initialiser creates a group of trees by
using the picture it is given and adding it a number of times (leaving a gap) to a
group representing a row of trees. It then adds that group to the larger group
representing a group of tree rows. Notice the use of integer division, “//”, to divide
the “gapsize”. Without it, dividing gapsize by 2 may give a half and not a whole
number (an integer).
The update part of the class defines what a group of trees can do when it is
updated. The group will take all the rows of trees within it and move them up by a
small distance. Also, when the row of trees goes behind the skier, off the top of
the screen, it will remove that row of trees.