Why is my ball vector retaining its components after reinit? - vector

Question

I'm writing a Pong game with Pygame and this is the code for my Ball class so far:
class Ball(pygame.sprite.Sprite):
def __init__(self, game, vector=Vec2D.Vec2D()):
super(Ball, self).__init__()
self.image = pygame.Surface((BALL_RADIUS*2, BALL_RADIUS*2))
self.rect = self.image.get_rect()
self.__draw_ball()
screen = pygame.display.get_surface()
self.area = screen.get_rect().inflate(-GAP*2, 0)
self.vector = vector
self.game = game
self.reinit()
def __draw_ball(self):
self.image.fill(BLACK)
self.image.set_colorkey(BLACK, RLEACCEL)
pygame.draw.circle(self.image, WHITE, (self.rect.centerx, self.rect.centery), BALL_RADIUS)
def reinit(self):
self.rect.centerx = self.area.centerx
self.rect.centery = self.area.centery
self.vector = Vec2D.Vec2D.from_magn_and_angle(BALL_SPEED, 0)
def update(self):
self.rect = self.calcnewpos()
self.handle_collision()
def calcnewpos(self):
(dx, dy) = self.vector.get_xy()
return self.rect.move(dx, dy)
def handle_collision(self):
(dx, dy) = self.vector.get_xy()
if not self.area.contains(self.rect):
if self.__hit_topbottom():
dy = -dy
elif self.__hit_leftright():
self.game.increase_score()
self.reinit()
else:
for paddle in self.hit_paddle(dx):
if dx < 0: self.rect.left = GAP + PADDLE_WIDTH
elif dx > 0: self.rect.right = SCREEN_WIDTH - (GAP + PADDLE_WIDTH)
dx = -dx
dy = paddle.hitpos / 4
paddle.collided = True
self.vector = Vec2D.Vec2D(dx, dy)
def _hit_topbottom(self):
return self.rect.top < 0 or self.rect.bottom > SCREEN_HEIGHT
def _hit_leftright(self):
return self.rect.left < self.area.left or self.rect.right > self.area.right
def hit_paddle(self, dx):
if dx < 0: paddle = self.game.paddles['left']
elif dx > 0: paddle = self.game.paddles['right']
if self.rect.colliderect(paddle.rect): return [paddle]
else: return []
Well, after the player (or the AI) scores, the ball calls its reinit method that places the ball in the middle of the screen and resets the vector:
def reinit(self):
self.rect.centerx = self.area.centerx
self.rect.centery = self.area.centery
self.vector = Vec2D.Vec2D.from_magn_and_angle(BALL_SPEED, 0)
But, somehow, the ball still maintains the vector it had before reinit was called. So when the ball gets through the left side with a vector like (-5.0 -2.0), it changes quickly in the reinit call and then change back to (-5.0, -2.0). Can someone please tell me why this is happening?

Answer 1

The problem, is in your handle_collision method.
The short story:
The first thing the function does, is set dx and dy to the current vector. Then it calls reinit(). Then, it sets them back to what the first were at the end of the function.
To fix:
Change
def handle_collision(self):
(dx, dy) = self.vector.get_xy() # <-- It first sets (dx, dy) to the old vector
if not self.area.contains(self.rect):
if self.__hit_topbottom():
...
elif self.__hit_leftright():
... # <-- here is where the reinit gets called, which changes the vector to new values.
else:
for paddle in self.hit_paddle(dx):
...
self.vector = Vec2D.Vec2D(dx, dy) # <-- Then the vector gets changed again, to the OLD vector saved above in (dx, dy)
To
def handle_collision(self):
(dx, dy) = self.vector.get_xy()
if not self.area.contains(self.rect):
if self.__hit_topbottom():
...
elif self.__hit_leftright():
...
return # <-- With the return here, the parsing never gets to change it back
else:
for paddle in self.hit_paddle(dx):
...
self.vector = Vec2D.Vec2D(dx, dy)
This will prevent the vector getting set back to what it was, while still setting it when it needs to be.