python – How do I detect collision in pygame?

In PyGame, basic collision detection can be done using pygame.Rect objects. The Rect object offers various methods for detecting collisions between objects. Note that even the collision of a rectangular object with a circular object such as a paddle and a ball in Pong game can be roughly detected by a collision between two rectangular objects, the paddle and the bounding rectangle of the ball.

Some examples:

  • pygame.Rect.collidepoint:

    Test if a point is inside a rectangle

    repl.it/@Rabbid76/PyGame-collidepoint

    import pygame
    
    pygame.init()
    window = pygame.display.set_mode((250, 250))
    rect = pygame.Rect(*window.get_rect().center, 0, 0).inflate(100, 100)
    
    run = True
    while run:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                run = False
    
        point = pygame.mouse.get_pos()
        collide = rect.collidepoint(point)
        color = (255, 0, 0) if collide else (255, 255, 255)
    
        window.fill(0)
        pygame.draw.rect(window, color, rect)
        pygame.display.flip()
    
    pygame.quit()
    exit()
    
  • pygame.Rect.colliderect

    Test if two rectangles overlap

    See also How to detect collisions between two rectangular objects or images in pygame

    repl.it/@Rabbid76/PyGame-colliderect

    colliderect

    import pygame
    
    pygame.init()
    window = pygame.display.set_mode((250, 250))
    rect1 = pygame.Rect(*window.get_rect().center, 0, 0).inflate(75, 75)
    rect2 = pygame.Rect(0, 0, 75, 75)
    
    run = True
    while run:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                run = False
    
        rect2.center = pygame.mouse.get_pos()
        collide = rect1.colliderect(rect2)
        color = (255, 0, 0) if collide else (255, 255, 255)
    
        window.fill(0)
        pygame.draw.rect(window, color, rect1)
        pygame.draw.rect(window, (0, 255, 0), rect2, 6, 1)
        pygame.display.flip()
    
    pygame.quit()
    exit()
    

. pygame.Rect.collidelist and pygame.Rect.collidelistall can be used for the collision test between a rectangle and a list of rectangles. pygame.Rect.collidedict and pygame.Rect.collidedictall can be used for the collision test between a rectangle and a dictionary of rectangles.

The collision pygame.sprite.Sprite and pygame.sprite.Group objects, can be detected by pygame.sprite.spritecollide(), pygame.sprite.groupcollide() or pygame.sprite.spritecollideany(). When using these methods, the collision detection algorithm can be specified by the collided argument:

The collided argument is a callback function used to calculate if two sprites are colliding.

Possible collided callables are collide_rect, collide_rect_ratio, collide_circle, collide_circle_ratio, collide_mask

Some examples:

  • pygame.sprite.spritecollide()

    repl.it/@Rabbid76/PyGame-spritecollide

    import pygame
    
    pygame.init()
    window = pygame.display.set_mode((250, 250))
    
    sprite1 = pygame.sprite.Sprite()
    sprite1.image = pygame.Surface((75, 75))
    sprite1.image.fill((255, 0, 0))
    sprite1.rect = pygame.Rect(*window.get_rect().center, 0, 0).inflate(75, 75)
    sprite2 = pygame.sprite.Sprite()
    sprite2.image = pygame.Surface((75, 75))
    sprite2.image.fill((0, 255, 0))
    sprite2.rect = pygame.Rect(*window.get_rect().center, 0, 0).inflate(75, 75)
    
    all_group = pygame.sprite.Group([sprite2, sprite1])
    test_group = pygame.sprite.Group(sprite2)
    
    run = True
    while run:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                run = False
    
        sprite1.rect.center = pygame.mouse.get_pos()
        collide = pygame.sprite.spritecollide(sprite1, test_group, False)
    
        window.fill(0)
        all_group.draw(window)
        for s in collide:
            pygame.draw.rect(window, (255, 255, 255), s.rect, 5, 1)
        pygame.display.flip()
    
    pygame.quit()
    exit()
    

For a collision with masks see How can I made a collision mask? or Pygame mask collision

See also Collision and Intersection

  • pygame.sprite.spritecollide() / collide_circle

    repl.it/@Rabbid76/PyGame-spritecollidecollidecircle

    import pygame
    
    pygame.init()
    window = pygame.display.set_mode((250, 250))
    
    sprite1 = pygame.sprite.Sprite()
    sprite1.image = pygame.Surface((80, 80), pygame.SRCALPHA)
    pygame.draw.circle(sprite1.image, (255, 0, 0), (40, 40), 40)
    sprite1.rect = pygame.Rect(*window.get_rect().center, 0, 0).inflate(40, 40)
    sprite2 = pygame.sprite.Sprite()
    sprite2.image = pygame.Surface((80, 89), pygame.SRCALPHA)
    pygame.draw.circle(sprite2.image, (0, 255, 0), (40, 40), 40)
    sprite2.rect = pygame.Rect(*window.get_rect().center, 0, 0).inflate(80, 80)
    
    all_group = pygame.sprite.Group([sprite2, sprite1])
    test_group = pygame.sprite.Group(sprite2)
    
    run = True
    while run:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                run = False
    
        sprite1.rect.center = pygame.mouse.get_pos()
        collide = pygame.sprite.spritecollide(sprite1, test_group, False, pygame.sprite.collide_circle)
    
        window.fill(0)
        all_group.draw(window)
        for s in collide:
            pygame.draw.circle(window, (255, 255, 255), s.rect.center, s.rect.width // 2, 5)
        pygame.display.flip()
    
    pygame.quit()
    exit()
    

What does this all mean for your code?

pygame.Surface.get_rect.get_rect() returns a rectangle with the size of the Surface object, that always starts at (0, 0) since a Surface object has no position. The position of the rectangle can be specified by a keyword argument. For example, the center of the rectangle can be specified with the keyword argument center. These keyword arguments are applied to the attributes of the pygame.Rect before it is returned (see pygame.Rect for a full list of the keyword arguments).
See *Why is my collision test always returning ‘true’ and why is the position of the rectangle of the image always wrong (0, 0)?

You don’t need the x and y attributes of Sprite and Bullet at all. Use the position of the rect attribute instead:

#Define the sprite class
class Sprite:
    def __init__(self, x, y, name):
        self.image = pygame.image.load(name)
        self.rect = self.image.get_rect(topleft = (x, y))

    def render(self):
        window.blit(self.image, self.rect)

# Define the bullet class to create bullets          
class Bullet:
    def __init__(self, x, y):
        self.bullet = pygame.image.load("user_bullet.BMP")
        self.rect = self.bullet.get_rect(topleft = (x + 23, y))

    def render(self):
        window.blit(self.bullet, self.rect)

Use pygame.Rect.colliderect() to detect collisions between instances of Sprite and Bullet.
See How to detect collisions between two rectangular objects or images in pygame:

my_sprite = Sprite(sx, sy, name)
my_bullet = Bullet(by, by)
while True:
    # [...]

    if my_sprite.rect.colliderect(my_bullet.rect):
        printe("hit")

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