Use mask function (for collision detection) with multiple sprites - pygame

Question

I am brand new to Pygame and am making a game for my A-level course. I am trying to have multiple bats that I can spawn and collide with. I am using Pygames mask function for 'pixel perfect collision' but I cannot get multiple bats to spawn at the same time with the collision system also working. I tried using groups but I haven't been able to get this to work. Does anyone know how to fix my code/ a better way around this problem? Thanks! The relevant code is below...
class Bat(pygame.sprite.Sprite):
def __init__(self, bat_x, bat_y):
pygame.sprite.Sprite.__init__(self)
self.bat1 = pygame.image.load("Sprites\Bat_enemy\Bat-1.png").convert_alpha() # For hit registration for bat
self.bat1 = pygame.transform.scale(self.bat1, (80, 70))
self.bat_mask = pygame.mask.from_surface(self.bat1)
self.bat_rect = self.bat1.get_rect()
self.bat_x = bat_x
self.bat_y = bat_y
bats = pygame.sprite.Group()
Then in main loop:
num_of_bats = [1]
#Bat#
for i in num_of_bats:
bat_x = (random.randint(0, 600))
bat_y = (random.randint(0, 600))
bat = Bat(bat_x, bat_y, i)
bats.add(bat)
for bat in bats:
offsetP2B = (int(x - batx), int(y - self.baty)) #Player to Bat
resultP2B = bat_mask.overlap(player_mask, offsetP2B)

Answer 1

First get rectangle based collision working, then worry about the bitmask accuracy!
There's a couple of problems with your Sprite. The big one is that PyGame uses sprite.image to draw the bitmap. Your sprite code is using bat1 instead. It also needs to position the sprite.rect to the co-ordinate of the Bat. Furthermore, the collision mask must be called mask, and the sprite's collision/position pygame.Rect must be called rect.
I'm not sure if it's just a paste-o, but the sprite group definition shouldn't be inside the Sprite class.
So ... with a few minor fixups:
class Bat(pygame.sprite.Sprite):
def __init__(self, bat_x, bat_y, bat_image):
pygame.sprite.Sprite.__init__(self)
self.image = bat_image
self.rect = self.image.get_rect()
self.mask = pygame.mask.from_surface( self.image )
self.rect.centre = ( bat_x, bat_y )
def update( self ):
# TODO: code to make this bat move/flat whatever
pass
There's only minor differences here. It's better to load the image in once, outside the sprite class, than loading it in hundreds(?) of times - once for each bat.
Now it's pretty easy to make a colony of bats:
import os.path
START_BAT_COUNT = 30
BAT_IMAGE_PATH = os.path.join( 'Sprites', 'Bat_enemy', 'Bat-1.png' )
# group to hold all the bat sprites
all_bats = pygame.sprite.Group()
# Going Batty!
bat_image = pygame.image.load( BAT_IMAGE_PATH ).convert_alpha()
for i in range( START_BAT_COUNT ):
bat_x = (random.randint(0, 600))
bat_y = (random.randint(0, 600))
new_bat = Bat( bat_x, bat_y, bat_image )
all_bats.add( new_bat )
The in your main loop:
# move every bat
all_bats.update()
...
# paint every bat
all_bats.draw( screen )