PyGame Basics

Collision

In games, when an object touches another object or boundary, we call it a collision. As an event that we want to handle.

Here, let's spin the ball and reverse it's direction whenever the hand hits the ball.

First, let's set a spin flag and set the movements for the ball.


          class Ball(pygame.sprite.Sprite):
    """Bounce a ball around the screen. It can spin when it is hit."""

    def __init__(self):
        pygame.sprite.Sprite.__init__(self)  # call Sprite intializer
        self.screen = pygame.display.get_surface()
        self.image = pygame.image.load("ball.png")
        self.rect = self.image.get_rect()
        self.speed = [2, 2]
        self.spin = 0

    def update(self):
        """move or spin, depending on the spin state"""
        if self.spin:
            self._spin()
        else:
            self._move()

    def _move(self):
        """move the ball across the screen, reverse speed at the ends"""
        self.rect = self.rect.move(self.speed)
        if self.rect.left < 0 or self.rect.right > WIDTH:
            self.speed[0] = -self.speed[0]
        if self.rect.top < 0 or self.rect.bottom > HEIGHT:
            self.speed[1] = -self.speed[1]

    def _spin(self):
        """spin the ball image"""
        center = self.rect.center
        self.spin += 60
        if self.spin >= 360:
            self.spin = 0
            self.image = self.original
        else:
            rotate = pygame.transform.rotate
            self.image = rotate(self.original, self.spin)
        self.rect = self.image.get_rect(center=center)

    def hit(self):
        """this will cause the ball to start spinning"""
        if not self.spin:
            self.spin = 60
            self.original = self.image
            # Reverse direction
            self.speed = [-x for x in self.speed]

We now do the same for the hand. Add a hit flag and check for collision with the ball and return True or False if collision occurs.


            class Hand(pygame.sprite.Sprite):
    """moves a hand icon on the screen, following the mouse"""

    def __init__(self):
        pygame.sprite.Sprite.__init__(self)  # call Sprite initializer
        self.image = pygame.image.load("hand.png")
        self.rect = self.image.get_rect()
        self.hitting = 0

    def update(self):
        """move the hand based on the mouse position"""
        pos = pygame.mouse.get_pos()
        self.rect.midtop = pos
        if self.hitting:
            self.rect.move_ip(5, 10)

    def hit(self, target):
        """returns true if the hand collides with the target"""
        if not self.hitting:
            self.hitting = 1
            hitbox = self.rect.inflate(-5, -5)
            return hitbox.colliderect(target.rect)

    def unhit(self):
        """called to pull the hand back"""
        self.hitting = 0

Handle events

To trigger the actions, we will need to handle it in the check_events loop.


                def check_events(self):
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                self.running = False
            elif event.type == pygame.KEYDOWN and event.key == pygame.K_ESCAPE:
                self.running = False
            elif event.type == pygame.MOUSEBUTTONDOWN:
                if self.hand.hit(self.ball):
                    self.ball.hit()
            elif event.type == pygame.MOUSEBUTTONUP:
                self.hand.unhit()
        return

Now, play the game!! 🎈