pygame 中的加速和减速

Question

我没有太多的编码经验，我一直在尝试让我的角色在按住键时加速到恒定速度，在松开键时减速。我在网上找到了一些代码，但我似乎无法将其正确实施到我的代码中。如果您不介意，如果您彻底解释了答案，那将会很有帮助，这样我才能正确理解我做错了什么。

这是我的代码

"""Dot Game"""

#Imports
import pygame, sys

#Constants
WIDTH, HEIGHT = 1000, 1000
TITLE = "Dot."

#pygame initialization
pygame.init()
win = pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption(TITLE)
#fps
FPS = 60
fpsclock = pygame.time.Clock()

#colors
bgc = (247, 226, 222)
pc = (152, 193, 217)
pc2 = (61, 90, 128)
ec = (119, 2, 26)
ec2 = (220, 66, 73)

#accel
x_change = 0
y_change = 0
accel_x = 0
accel_y = 0
max_speed = 6

display_width, display_height = pygame.display.get_surface().get_size()
x = display_width * 0.45
y = display_height * 0.8

#Player Class
class Player:
    def __init__(self, x, y):
        self.x = int(x)
        self.y = int(y)
        self.radius = 32
        self.width = 2
        self.color = pc
        self.color2 = pc2
        self.velX = 0
        self.velY = 0
        self.left_pressed = False
        self.right_pressed = False
        self.up_pressed = False
        self.down_pressed = False
        self.speed = 3
        self.hitbox = (self.x -20, self.y -20, 40, 40)
    
    def draw(self, win):
        pygame.draw.circle(win, self.color2, (self.x,self.y), 20)
        pygame.draw.circle(win, self.color, (self.x,self.y), 14)
        self.hitbox = (self.x -20, self.y -20, 40, 40)
        #pygame.draw.rect(win,(255,0,0), self.hitbox,2)
    
    def update(self):
        self.velX = 0
        self.velY = 0
        if self.left_pressed:
            self.velX = -self.speed
        if self.right_pressed:
            self.velX = self.speed
        if self.up_pressed:
            self.velY = -self.speed
        if self.down_pressed :
            self.velY = self.speed
        
        self.x += self.velX
        self.y += self.velY

        self.rect = pygame.Rect(int(self.x), int(self.y), 32, 32)

    def collide(self):
        print('hit')
        pass

#Player Initialization
player = Player(WIDTH/2, HEIGHT/2)

#Main Loop
collide = False
while not collide:

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            collide == True
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                accel_x = -.2
                player.left_pressed = True
            elif event.key == pygame.K_RIGHT:
                accel_x = .2
                player.right_pressed = True
            elif event.key == pygame.K_UP:
                accel_y = -.2
                player.up_pressed = True
            elif event.key == pygame.K_DOWN:
                accel_y = .2
                player.down_pressed = True
        elif event.type == pygame.KEYUP:
            if event.key == pygame.K_LEFT:
                accel_x = 0
                accel_y = 0
                player.left_pressed = False
            elif event.key == pygame.K_RIGHT:
                accel_x = 0
                accel_y = 0
                player.right_pressed = False
            elif event.key == pygame.K_UP:
                accel_x = 0
                accel_y = 0
                player.up_pressed = False
            elif event.key == pygame.K_DOWN:
                accel_x = 0
                accel_y = 0
                player.down_pressed = False
    
    x_change += accel_x  # Accelerate.
    if abs(x_change) >= max_speed:  # If max_speed is exceeded.
        # Normalize the x_change and multiply it with the max_speed.
        x_change = x_change/abs(x_change) * max_speed

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

    # Decelerate if no key is pressed.
    if accel_x == 0:
        if x_change > 0:
            x_change -= 0.2
            if x_change < 0.2:
                x_change = 0
        elif x_change < 0:
            x_change += 0.2
            if x_change > -0.2:
                x_change = 0
    if accel_y == 0:
        if y_change > 0:
            y_change -= 0.2
            if y_change < 0.2:
                y_change = 0
        elif y_change < 0:
            y_change += 0.2
            if y_change > -0.2:
                y_change = 0

    x += x_change  # Move the object.
    y += y_change

    #Draw
    win.fill((bgc))  
    player.draw(win)

    #update
    player.update()
    pygame.display.update()

    fpsclock.tick(FPS)

运动本身起作用，但没有加减速

Answer 1

在您的代码中，速度始终是恒定的，因为您在 update 的开头设置了 self.velX = 0 和 self.velY = 0。因此，速度的数量始终为 0 或 3。不要重置 self.velX 和 self.velY。随加速度改变速度，但限制在最大速度。加速度必须是一个小值。只要按下一个键，这个小值就会每帧添加一次速度。这样慢慢地把速度提高到最大。
通过将速度乘以摩擦力来改进物理学。摩擦值必须小于 1，或者 1 表示没有摩擦：

class Player:
    def __init__(self, x, y):
        # [...]

        self.acceleration = 0.1
        self.friction = 0.99 # = 1   if you don't want any friction

    def update(self):
        if self.left_pressed:
            if self.velX > -max_speed:
                self.velX -= self.acceleration
        if self.right_pressed:
            if self.velX < max_speed:
                self.velX += self.acceleration
        if self.up_pressed:
            if self.velY > -max_speed:
                self.velY -= self.acceleration
        if self.down_pressed :
            if self.velY < max_speed:
                self.velY += self.acceleration
        
        self.x += self.velX
        self.y += self.velY
        self.velX *= self.friction
        self.velY *= self.friction

        self.rect = pygame.Rect(int(self.x), int(self.y), 32, 32)

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