如何使用PyGame淡入和淡出屏幕？

Question

因此，在尝试使用PyGame完成游戏关卡后，我试图淡出屏幕，然后再恢复。我的问题是，只有fadeout（）有效，而不是fadein（）有效。当调用fadein（）时，屏幕会变黑几秒钟，然后突然显示下一个级别。我找不到问题，有什么想法吗？

def fadeout():
    fadeout = pg.Surface((screen_width, screen_height))
    fadeout = fadeout.convert()
    fadeout.fill(black)
    for i in range(255):
        fadeout.set_alpha(i)
        screen.blit(fadeout, (0, 0))
        pg.display.update()


def fadein():
    fadein = pg.Surface((screen_width, screen_height))
    fadein = fadein.convert()
    fadein.fill(black)
    for i in range(255):
        fadein.set_alpha(255-i)
        screen.blit(fadein, (0, 0))
        pg.display.update()

Answer 1

您的问题是淡入黑屏，因此看不到任何效果。黑色屏幕Surface上面画有半透明的黑色，仍然是黑色Surface。

您应该渲染关卡的第一帧，并Surface在将fadein表面拖拉到屏幕上之前将其拉宽到屏幕上。

这是我一起破解的一个简单示例。按一个键可从一个场景切换到下一场景。

import pygame
import random
from itertools import cycle

class Cloud(pygame.sprite.Sprite):
    def __init__(self, x, y):
        super().__init__()
        self.image = pygame.Surface((50, 20))
        self.image.set_colorkey((11, 12, 13))
        self.image.fill((11, 12, 13))
        pygame.draw.ellipse(self.image, pygame.Color('white'), self.image.get_rect())
        self.rect = self.image.get_rect(topleft=(x,y))

    def update(self, dt, events):
        self.rect.move_ip(dt/10, 0)
        if self.rect.left >= pygame.display.get_surface().get_rect().width:
            self.rect.right = 0

class DayScene:
    def __init__(self):
        self.clouds = pygame.sprite.Group(Cloud(0, 30), Cloud(100, 40), Cloud(400, 50))

    def draw(self, screen):
        screen.fill(pygame.Color('lightblue'))
        self.clouds.draw(screen)

    def update(self, dt, events):
        self.clouds.update(dt, events)

class NightScene:
    def __init__(self):
        sr = pygame.display.get_surface().get_rect()
        self.sky = pygame.Surface(sr.size)
        self.sky.fill((50,0,50))
        for x in random.sample(range(sr.width), 50):
            pygame.draw.circle(self.sky, (200, 200, 0), (x, random.randint(0, sr.height)), 1)
        self.clouds = pygame.sprite.Group(Cloud(70, 70), Cloud(60, 40), Cloud(0, 50), Cloud(140, 10), Cloud(100, 20))

    def draw(self, screen):
        screen.blit(self.sky, (0, 0))
        self.clouds.draw(screen)

    def update(self, dt, events):
        self.clouds.update(dt, events)

class Fader:

    def __init__(self, scenes):
        self.scenes = cycle(scenes)
        self.scene = next(self.scenes)
        self.fading = None
        self.alpha = 0
        sr = pygame.display.get_surface().get_rect()
        self.veil = pygame.Surface(sr.size)
        self.veil.fill((0, 0, 0))

    def next(self):
        if not self.fading:
            self.fading = 'OUT'
            self.alpha = 0

    def draw(self, screen):
        self.scene.draw(screen)
        if self.fading:
            self.veil.set_alpha(self.alpha)
            screen.blit(self.veil, (0, 0))

    def update(self, dt, events):
        self.scene.update(dt, events)

        if self.fading == 'OUT':
            self.alpha += 8
            if self.alpha >= 255:
                self.fading = 'IN'
                self.scene = next(self.scenes)
        else:
            self.alpha -= 8
            if self.alpha <= 0:
                self.fading = None

def main():
    screen_width, screen_height = 300, 300
    screen = pygame.display.set_mode((screen_width, screen_height))
    clock = pygame.time.Clock()
    dt = 0
    fader = Fader([DayScene(), NightScene()])

    while True:
        events = pygame.event.get()
        for e in events:
            if e.type == pygame.QUIT:
                return
            if e.type == pygame.KEYDOWN:
                fader.next()

        fader.draw(screen)
        fader.update(dt, events)

        pygame.display.flip()
        dt = clock.tick(30)

main()

通过将每个场景抽象到其自己的类中并将场景更改委派给Fader该类，我们能够让场景继续（或添加一个简单的if语句来防止这种情况）并在褪色时处理事件。