为什么Alpha混合无法正常工作？ [Pygame]

Question

我正在尝试创建一个简单的Pyame应用程序，其中将一些颜色与它们下面的颜色混合。这是我的代码：

代码列表1：

import pygame, sys, time
from pygame.locals import *

#define constants
WINDOW_WIDTH = 600
WINDOW_HEIGHT = 600
FPS = 60

pygame.init()
clock = pygame.time.Clock()
screen = pygame.display.set_mode((WINDOW_WIDTH, WINDOW_HEIGHT), 0, 32)

alpha = 0
increasing = True

while True:
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()

    #fill screen with red
    screen.fill(pygame.Color(247, 25, 0,255))
    alpha_surface = pygame.Surface((screen.get_rect().width, screen.get_rect().height))
    alpha_surface = alpha_surface.convert_alpha()
    surfaceRect = alpha_surface.get_rect()

    #fill surface with orange
    pygame.draw.rect(alpha_surface, (247, 137, 0, 255), (0, 0, 480, 480))
    #fill surface with translucent yellow
    pygame.draw.rect(alpha_surface, (220, 247, 0, alpha), (120, 120, 360, 360))
    #fill surface with green
    pygame.draw.rect(alpha_surface, (0, 247, 4), (240, 240, 240, 240))
    #fill surface with translucent blue
    pygame.draw.rect(alpha_surface, (0, 78, 247, alpha), (360, 360, 120, 120))
    screen.blit(alpha_surface, (120,120))

    pygame.display.update()
    clock.tick(FPS)

    if increasing:
        alpha += 1
        if alpha > 255:
            alpha = 255
            increasing = False
    else:
        alpha -= 1
        if alpha < 0:
            alpha = 0
            increasing = True

该代码应该可以使黄色矩形与橙色矩形融合在一起，而蓝色矩形与绿色矩形融合在一起。相反，我从中得到了一些东西：

图1：原始状态，黄色和蓝色不透明度设置为0％
Here is the extended information

对此：

图2：：黄色和蓝色不透明度设置为100％的最终状态

如您所见，黄色和蓝色矩形不仅与红色矩形（屏幕表面）融合在一起，而且还在橙色和绿色矩形上打了一个洞，以便我们可以通过它们看到红色矩形。

Answer 1

如果要混合不同的图层，则必须创建不同的pygame.Surface或图像。请注意pygame.image生成曲面。

创建一个表面并使其完全透明。此测量用pygame.Color(0, 0, 0, 0)填充：

alpha_surface1 = pygame.Surface( (screen.get_rect().width, screen.get_rect().height) )
alpha_surface1 = alpha_surface1.convert_alpha()
alpha_surface1.fill( pygame.Color(0, 0, 0, 0) )

在所需的表面上绘制任何东西，例如矩形

pygame.draw.rect(alpha_surface1, (247, 137, 0, 255), (120, 120, 480, 480))

blit()屏幕上的表面：

screen.blit(alpha_surface1, (0,0))

在多个表面重复此操作

例如

#fill screen with red
screen.fill(pygame.Color(247, 25, 0,255))

#fill surface with orange
alpha_surface1 = pygame.Surface( (screen.get_rect().width, screen.get_rect().height) )
alpha_surface1 = alpha_surface1.convert_alpha()
alpha_surface1.fill( pygame.Color(0, 0, 0, 0) )
pygame.draw.rect(alpha_surface1, (247, 137, 0, 255), (120, 120, 480, 480))

#fill surface 2 with translucent yellow
alpha_surface2 = pygame.Surface( (screen.get_rect().width, screen.get_rect().height) )
alpha_surface2 = alpha_surface2.convert_alpha()
alpha_surface2.fill( pygame.Color(0, 0, 0, 0) )
pygame.draw.rect(alpha_surface2, (220, 247, 0, alpha), (240, 240, 360, 360))

#fill surface 3 with green
alpha_surface3 = pygame.Surface( (screen.get_rect().width, screen.get_rect().height) )
alpha_surface3 = alpha_surface3.convert_alpha()
alpha_surface3.fill( pygame.Color(0, 0, 0, 0) )
pygame.draw.rect(alpha_surface3, (0, 247, 4), (360, 360, 240, 240) )

#fill surface 4 with translucent blue
alpha_surface4 = pygame.Surface( (screen.get_rect().width, screen.get_rect().height) )
alpha_surface4 = alpha_surface4.convert_alpha()
alpha_surface4.fill( pygame.Color(0, 0, 0, 0) )
pygame.draw.rect(alpha_surface4, (0, 78, 247, alpha), (480, 480, 120, 120) )

# blend surface1 on screen
screen.blit(alpha_surface1, (0,0))
# blend surface2 on screen
screen.blit(alpha_surface2, (0,0))
# blend surface3 on screen
screen.blit(alpha_surface3, (0,0))
# blend surface4 on screen
screen.blit(alpha_surface4, (0,0))