pygame如何移动用户控制的物体直到释放按键？

Question

我最近在玩pygame，一个用来做游戏的库。有个StackOverflow的老手给了我一些建议，帮我改进代码，让角色在屏幕上移动。目前的情况是，每次按下键盘，角色就会移动，但会慢下来然后停下，只有再次按下键时才会继续移动。有没有人能帮我，让角色在松开键时能够减速并停下呢？

非常感谢你们！

import sys
import pygame
import os
from pygame.locals import *

character = "toon.png"
bg = "bg.jpg"

delta = {
    pygame.K_LEFT: (-10, 0),
    pygame.K_RIGHT: (+10, 0),
    pygame.K_UP: (0, -10),
    pygame.K_DOWN: (0, +10),
    }

class Toon(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.image.load(character)
        self.bg = pygame.image.load(bg)
        self.rect = self.image.get_rect()
        self.speed = [2, 2]
        self.area = pygame.display.get_surface().get_rect()
    def update(self):
        self.rect = self.rect.move(self.speed)
        if self.rect.left < 0 or self.rect.right > self.area.width:
            self.speed[0] = -self.speed[0]
        if self.rect.top < 0 or self.rect.bottom > self.area.height:
            self.speed[1] = -self.speed[1]

class Main(object):
    def __init__(self):
        self.setup()
    def setup(self):
        pygame.init()
        size = (self.width, self.height) = (640,360)
        self.black = (0, 0, 0)
        self.bg = pygame.image.load(bg)
        self.screen = pygame.display.set_mode(size, 0, 32)
        self.toon = Toon()
        self.setup_background()
    def setup_background(self):
        self.background = pygame.Surface(self.screen.get_size())
        self.background = self.background.convert()
        self.screen.blit(self.bg, (0, 0))
        pygame.display.flip()
    def draw(self):
        self.screen.blit(self.bg, (0, 0))
        self.screen.blit(self.toon.image, self.toon.rect)
        pygame.display.flip()
    def event_loop(self):
        toon = self.toon
        while True:
            for event in pygame.event.get():
                if event.type == QUIT:
                    pygame.quit()
                    sys.exit()
                elif event.type == pygame.KEYDOWN:
                    deltax, deltay = delta.get(event.key, (0, 0))
                    toon.speed[0] += deltax
                    toon.speed[1] += deltay
            toon.speed[0] *= 0.95
            toon.speed[1] *= 0.95
            toon.update()
            self.draw()
            pygame.time.delay(10)

if __name__ == '__main__':
    app = Main()
    app.event_loop()

Answer 1

在按下键盘的过程中，把 friction = 1 设置为1，而在松开键盘时，把 friction < 1 设置为小于1：

            elif event.type == pygame.KEYDOWN:
                deltax, deltay = delta.get(event.key, (0, 0))
                toon.speed[0] += deltax
                toon.speed[1] += deltay
                friction = 1
            elif event.type == pygame.KEYUP:
                friction = 0.95
        toon.speed = [x*friction for x in toon.speed]

---

import sys
import pygame
import os
from pygame.locals import *

character = "toon.png"
bg = "bg.jpg"

delta = {
    pygame.K_LEFT: (-10, 0),
    pygame.K_RIGHT: (+10, 0),
    pygame.K_UP: (0, -10),
    pygame.K_DOWN: (0, +10),
    }

class Toon(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.image.load(character)
        self.bg = pygame.image.load(bg)
        self.rect = self.image.get_rect()
        self.speed = [0, 0]
        self.area = pygame.display.get_surface().get_rect()
    def update(self):
        self.rect = self.rect.move(self.speed)
        if self.rect.left < 0 or self.rect.right > self.area.width:
            self.speed[0] = -self.speed[0]
        if self.rect.top < 0 or self.rect.bottom > self.area.height:
            self.speed[1] = -self.speed[1]

class Main(object):
    def __init__(self):
        self.setup()
    def setup(self):
        pygame.init()
        size = (self.width, self.height) = (640,360)
        self.black = (0, 0, 0)
        self.bg = pygame.image.load(bg)
        self.screen = pygame.display.set_mode(size, 0, 32)
        self.toon = Toon()
        self.setup_background()
    def setup_background(self):
        self.background = pygame.Surface(self.screen.get_size())
        self.background = self.background.convert()
        self.screen.blit(self.bg, (0, 0))
        pygame.display.flip()
    def draw(self):
        self.screen.blit(self.bg, (0, 0))
        self.screen.blit(self.toon.image, self.toon.rect)
        pygame.display.flip()
    def event_loop(self):
        toon = self.toon
        friction = 1        
        while True:
            for event in pygame.event.get():
                if event.type == QUIT:
                    pygame.quit()
                    sys.exit()
                elif event.type == pygame.KEYDOWN:
                    deltax, deltay = delta.get(event.key, (0, 0))
                    toon.speed[0] += deltax
                    toon.speed[1] += deltay
                    friction = 1
                elif event.type == pygame.KEYUP:
                    friction = 0.95
            toon.speed = [x*friction for x in toon.speed]
            toon.update()
            self.draw()
            pygame.time.delay(10)

if __name__ == '__main__':
    app = Main()
    app.event_loop()

Answer 2

我建议你修改一下你的 Main.event_loop() 方法，并在 Main 类中添加另一个函数，这个函数会使用 pygame.key.get_pressed：

def event_loop(self):
    toon = self.toon
    while True:
        self.event_handle()
        toon.speed[0] *= 0.95
        toon.speed[1] *= 0.95
        toon.update()
        self.draw()
        pygame.time.delay(10)

def event_handle(self):
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
    # This will allow diagonal movements.. 
    key = pygame.key.get_pressed()
    if key[pygame.K_LEFT]:
        self.toon.speed[0] = -10
    if key[pygame.K_RIGHT]:
        self.toon.speed[0] = +10
    if key[pygame.K_UP]:
        self.toon.speed[1] = -10
    if key[pygame.K_DOWN]:
        self.toon.speed[1] = +10

具体的修改：

1. 我添加了一个新函数，叫做 event_handle，它会处理事件和按键。
2. 你会发现，原来的事件循环并没有处理按键。这是因为我们使用了 pygame.key.get_pressed，这个方法更适合当前的任务。
   
   • 它会返回一个布尔值列表，表示当前被按下的按键。我们可以通过索引 key 来检查我们想要的按键（这里是方向键）。

效果是：
你的问题解决了。