python - Pygame move 加速、平台游戏的问题

Question

当我使用右键向右 move 时，我会加速到最大速度。当我释放它时，我会减速停止，这样就很好。然而，当使用左键向左 move 时，松开左键后，我继续以固定速度 move ，然后不久后突然停止。知道我的代码可能有什么问题吗？

原代码来自http://programarcadegames.com/python_examples/show_file.php?file=platform_jumper.py

import pygame

# Global constants

# Colors
BLACK = (0, 0, 0)
WHITE = (255, 255, 255)
GREEN = (0, 255, 0)
RED = (255, 0, 0)
BLUE = (0, 0, 255)

# Screen dimensions
SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600


class Player(pygame.sprite.Sprite):
    """ This class represents the bar at the bottom that the player
        controls. """

    # -- Methods
    def __init__(self):
        """ Constructor function """

        # Call the parent's constructor
        super().__init__()

        # Create an image of the block, and fill it with a color.
        # This could also be an image loaded from the disk.
        width = 40
        height = 60
        self.image = pygame.Surface([width, height])
        self.image.fill(RED)

        # Set a referance to the image rect.
        self.rect = self.image.get_rect()

        # Set speed vector of player
        self.xVel = 0
        self.yVel = 0

        # List of sprites we can bump against
        self.level = None

    def update(self):
        """ Move the player. """
        # Gravity
        self.calc_grav()

        # Move left/right


        # See if we hit anything
        block_hit_list = pygame.sprite.spritecollide(self, self.level.platform_list, False)
        for block in block_hit_list:
            # If we are moving right,
            # set our right side to the left side of the item we hit
            if self.xVel > 0:
                self.rect.right = block.rect.left
            elif self.xVel < 0:
                # Otherwise if we are moving left, do the opposite.
                self.rect.left = block.rect.right

        # Move up/down
        self.rect.y += self.yVel

        # Check and see if we hit anything
        block_hit_list = pygame.sprite.spritecollide(self, self.level.platform_list, False)
        for block in block_hit_list:

            # Reset our position based on the top/bottom of the object.
            if self.yVel > 0:
                self.rect.bottom = block.rect.top
            elif self.yVel < 0:
                self.rect.top = block.rect.bottom

            # Stop our vertical movement
            self.yVel = 0

    def calc_grav(self):
        """ Calculate effect of gravity. """
        if self.yVel == 0:
            self.yVel = 1
        else:
            self.yVel += .35

        # See if we are on the ground.
        if self.rect.y >= SCREEN_HEIGHT - self.rect.height and self.yVel >= 0:
            self.yVel = 0
            self.rect.y = SCREEN_HEIGHT - self.rect.height

    def jump(self):
        """ Called when user hits 'jump' button. """

        # move down a bit and see if there is a platform below us.
        # Move down 2 pixels because it doesn't work well if we only move down
        # 1 when working with a platform moving down.
        self.rect.y += 2
        platform_hit_list = pygame.sprite.spritecollide(self, self.level.platform_list, False)
        self.rect.y -= 2

        # If it is ok to jump, set our speed upwards
        if len(platform_hit_list) > 0 or self.rect.bottom >= SCREEN_HEIGHT:
            self.yVel = -10




class Platform(pygame.sprite.Sprite):
    """ Platform the user can jump on """

    def __init__(self, width, height):
        """ Platform constructor. Assumes constructed with user passing in
            an array of 5 numbers like what's defined at the top of this
            code. """
        super().__init__()

        self.image = pygame.Surface([width, height])
        self.image.fill(GREEN)

        self.rect = self.image.get_rect()


class Level(object):
    """ This is a generic super-class used to define a level.
        Create a child class for each level with level-specific
        info. """

    def __init__(self, player):
        """ Constructor. Pass in a handle to player. Needed for when moving platforms
            collide with the player. """
        self.platform_list = pygame.sprite.Group()
        self.enemy_list = pygame.sprite.Group()
        self.player = player

        # Background image
        self.background = None

    # Update everythign on this level
    def update(self):
        """ Update everything in this level."""
        self.platform_list.update()
        self.enemy_list.update()

    def draw(self, screen):
        """ Draw everything on this level. """

        # Draw the background
        screen.fill(BLUE)

        # Draw all the sprite lists that we have
        self.platform_list.draw(screen)
        self.enemy_list.draw(screen)


# Create platforms for the level
class Level_01(Level):
    """ Definition for level 1. """

    def __init__(self, player):
        """ Create level 1. """

        # Call the parent constructor
        Level.__init__(self, player)

        # Array with width, height, x, and y of platform
        level = [[210, 70, 500, 500],
                 [210, 70, 200, 400],
                 [210, 70, 600, 300],
                 ]

        # Go through the array above and add platforms
        for platform in level:
            block = Platform(platform[0], platform[1])
            block.rect.x = platform[2]
            block.rect.y = platform[3]
            block.player = self.player
            self.platform_list.add(block)


def main():
    """ Main Program """
    pygame.init()

    # Set the height and width of the screen
    size = [SCREEN_WIDTH, SCREEN_HEIGHT]
    screen = pygame.display.set_mode(size)

    pygame.display.set_caption("Platformer Jumper")

    # Create the player
    player = Player()

    # Create all the levels
    level_list = []
    level_list.append(Level_01(player))

    # Set the current level
    current_level_no = 0
    current_level = level_list[current_level_no]

    active_sprite_list = pygame.sprite.Group()
    player.level = current_level

    player.rect.x = 340
    player.rect.y = SCREEN_HEIGHT - player.rect.height
    active_sprite_list.add(player)

    accel_x = 0
    max_speed = 6
    # Loop until the user clicks the close button.
    done = False

    # Used to manage how fast the screen updates
    clock = pygame.time.Clock()

    # -------- Main Program Loop -----------
    while not done:
        player_running = False
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                done = True

            elif event.type == pygame.KEYDOWN:
                if event.key == pygame.K_LEFT:
                    accel_x = -0.5
                if event.key == pygame.K_RIGHT:
                    accel_x = 0.5
                if event.key == pygame.K_SPACE:
                    player.jump()
            elif event.type == pygame.KEYUP:
                if event.key in (pygame.K_LEFT, pygame.K_RIGHT):
                    accel_x = 0

        player.xVel += accel_x  # Accelerate.
        if abs(player.xVel) >= max_speed:  # If max_speed is exceeded.
            # Normalize the x_change and multiply it with the max_speed.
            player.xVel = player.xVel / abs(player.xVel) * max_speed

        # Decelerate if no key is pressed.
        if accel_x == 0:
            player.xVel *= 0.5

        player.rect.x += player.xVel




        # Update the player.
        active_sprite_list.update()

        # Update items in the level
        current_level.update()

        # If the player gets near the right side, shift the world left (-x)
        if player.rect.right > SCREEN_WIDTH:
            player.rect.right = SCREEN_WIDTH

        # If the player gets near the left side, shift the world right (+x)
        if player.rect.left < 0:
            player.rect.left = 0

        # ALL CODE TO DRAW SHOULD GO BELOW THIS COMMENT
        current_level.draw(screen)
        active_sprite_list.draw(screen)

        # ALL CODE TO DRAW SHOULD GO ABOVE THIS COMMENT

        # Limit to 60 frames per second
        clock.tick(60)

        # Go ahead and update the screen with what we've drawn.
        pygame.display.flip()

    # Be IDLE friendly. If you forget this line, the program will 'hang'
    # on exit.
    pygame.quit()


if __name__ == "__main__":
    main()

Answer 1

引起该问题的原因是 pygame.Rect使用积分数据进行操作:

The coordinates for Rect objects are all integers. [...]

当你这样做时

player.rect.x += player.xVel

这与您所做的相同:

player.rect.x = int(player.rect.x + player.xVel)

player.xVel 的小数部分丢失。加法运算的结果被截断，玩家趋向于值较小的坐标(左)。

向类 Player 添加一个浮点 x 坐标 (self.px) 并用它来计算玩家的位置。使用round从 self.px 设置完整矩形位置:

class Player(pygame.sprite.Sprite):

    def __init__(self):
        # [...]
     
        # Set a referance to the image rect.
        self.rect = self.image.get_rect()
        self.px = self.rect.x

        # [...]

    def update(self):
        # [...]

        block_hit_list = pygame.sprite.spritecollide(self, self.level.platform_list, False)
        block_hit_list = pygame.sprite.spritecollide(self, self.level.platform_list, False)
        for block in block_hit_list:
            # If we are moving right,
            # set our right side to the left side of the item we hit
            if self.xVel > 0:
                self.rect.right = block.rect.left   
            elif self.xVel < 0:
                # Otherwise if we are moving left, do the opposite.
                self.rect.left = block.rect.right
            self.px = self.rect.x
  

def main():
    # [...]
 
    player.rect.x = 340
    player.px = player.rect.x

    # [...]

    while not done:
        # [...]

        player.px += player.xVel
        player.rect.x = round(player.px)
  
        # [...]