Problems with list of objects in python

Question

Hi I'm new to game dev and I'm using pygame, now I'm in this problem I have multiple enemies that the player has to avoid and kill simultaneously, but my collision detection function checks collision for one enemy at a time. Aside from the first enemy in the list, the function does not work for other enemies from the list. Here's the code for enemy creation and collision detection

class Enemy(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
        self.width, self.height = 30, 30
        self.vel = 10
        self.color = (0, 0, 255)
        self.rect = (x, y, self.width, self.height)

def create_enemies(n):
    enemies = []
    for i in range(n):
        xcor = randint(0, (W - 50))
        ycor = randint(0, H - H/2)
        enemies.append(Enemy(xcor, ycor))
    return enemies

n = 2

enemies = create_enemies(n)

def collision_detection(obj1, obj2list):
    for obj2 in obj2list:
        if (obj2.x < obj1.x < (obj2.x + obj2.width)) and (obj2.y < obj1.y < (obj2.y + obj2.height)):
            return False
        if (obj2.x < obj1.x < (obj2.x + obj2.width)) and (obj2.y < (obj1.y + obj1.height) < (obj2.y + obj2.height)):
            return False
        if (obj2.x < (obj1.x + obj1.width) < (obj2.x + obj2.width)) and (obj2.y < (obj1.y + obj1.height) < (obj2.y + obj2.height)):
            return False
        if (obj2.x < (obj1.x + obj1.width) < (obj2.x + obj2.width)) and (obj2.y < obj1.y < (obj2.y + obj2.height)):
            return False
        if obj1.x == obj2.x and obj1.y <= obj2.y + obj2.height:
            return False
        if obj1.x == obj2.x and obj1.y + obj1.height >= obj2.y:
            return False
        else:
            return True

Backticks for code format are `\``, not single quotes which are `'`. — Andras Deak -- Слава Україні, Jan 18 '20 at 09:12
`PyGame` has `pygame.Rect()` which has methods to check collisions and you don't have to write it - [player.rect.colliderect(enemy.rect)](https://www.pygame.org/docs/ref/rect.html#pygame.Rect.colliderect). It has also `Group` which can be used to check collision will list of enemies. — furas, Jan 18 '20 at 09:30

score 0 · Answer 1 · answered Jan 18 '20 at 09:14

Your problem is in your collision detection logic. Your logic is as follows:

main loop > call collision_detection > iterate over objects

It should be:

main loop > iterate over objects > call collision_detection

This is because if the first object in obj2list collides with obj1, it returns from the function and doesn't check the rest of the objects.

Problems with list of objects in python

1 Answers1