无法在pygame上向右移动玩家

Question

I am trying to write a Space Invaders game in pygame, but I cannot get the player to move right. Moving left works fine however.

My code for the Sprite and Player classes are:

class Sprite(pygame.sprite.Sprite):
    def __init__(self, x, y, image = None):
        pygame.sprite.Sprite.__init__(self)
        if image is None:
            self.image = pygame.Surface((25, 25))
            self.image.fill((0, 255, 0))
        else:
            self.image = image

        self.rect = self.image.get_rect()
        self.rect.x, self.rect.y = x, y
        self.speed = 0.5

    def moveLeft(self):
        self.rect.x -= self.speed

    def moveRight(self):
        self.rect.x += self.speed

    def draw(self):
        screen.blit(self.image, (self.rect.x, self.rect.y))


class Player(Sprite):
    def __init__(self, startpos):
        try:
            image = pygame.image.load(PLAYER_SPRITE_LOCATION)
        except: image = None
        Sprite.__init__(self, startpos[0], startpos[1], image)
        print("Player class initialized at %a with sprite %s" % (self.rect, self.image))
        self.score = 0

And the rest of the code is:

RESOLUTION = (224, 256)
PLAYERPOS  = [112, 220]

pygame.init()
screen = pygame.display.set_mode(RESOLUTION)

player = Player(PLAYERPOS)

end = False
fps = 60
clock = pygame.time.Clock()

printString = ""

PRINTFPS, time = pygame.USEREVENT+1, 1000
pygame.time.set_timer(PRINTFPS, time)
curr_fps = 0

invaders = pygame.sprite.Group()
bullets  = pygame.sprite.Group()
fullscreen = False
while not end:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            end = True
        if event.type == PRINTFPS:
            curr_fps = clock.get_fps()

    pressed = pygame.key.get_pressed()

    if pressed[pygame.K_LEFT] or pressed[pygame.K_a]:
        player.moveLeft()
    if pressed[pygame.K_RIGHT] or pressed[pygame.K_d]:
        player.moveRight()
    if pressed[pygame.K_SPACE] or pressed[pygame.K_s] or pressed[pygame.K_UP]:
        player.score += 1
    if pressed[pygame.K_F11]:
        if not fullscreen:
            screen = pygame.display.set_mode((0, 0), pygame.FULLSCREEN)
            fullscreen = True
        else:
            screen = pygame.display.set_mode(RESOLUTION)
            fullscreen = False
    # Print game data
    prevPrintString = printString
    printString = "\rPlayer: (%s, %s)" % (str("%.3f" % player.rect.x).zfill(7),
                                           str("%.3f" % player.rect.y).zfill(7))
    printString += "; Score: %i" % player.score
    printString += "; FPS: %s" % (str("%.2f" % curr_fps).zfill(5))
    if printString != prevPrintString:
        print(printString, end = "")

    # Background (not really needed)
    screen.fill((0, 0, 255)) # Blue screen!

    # Update sprites, e.g. invaders moving and bullets flying
    invaders.update()
    bullets.update()

    # Drawing sprites
    invaders.draw(screen)
    bullets.draw(screen)

    player.draw()

    # Update screen and maintain constant FPS
    clock.tick(fps)
    pygame.display.flip()

The problem is not that the input isn't working: I can tell that it does. I think the problem is with the moveRight function itself, and that somehow it maybe doesn't work with addition? But I don't know.

Thank you in advanced!

Answer 1

All of the fields stored in a pygame Rect are integers, but you are adding or substracting a fraction (0.5). My best guess is that when you subtract 0.5 from the x coordinate, it goes from (say) 112 to 111.5 and gets truncated to 111, so you move left one pixel. But if you add 0.5, it goes from 112 to 112.5 and gets truncated back to 112, so you don't move at all. I would suggest using whole numbers only.