python - 为什么 Alpha 混合不能正常工作？

Question

我正在尝试制作一个简单的 Pygame 应用程序，其中一些颜色与它们下面的颜色混合。这是我的代码:

代码 list 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

代码应该使黄色矩形与橙色矩形混合，蓝色矩形与绿色矩形混合。相反，我得到了一些来自于此的东西:

图 1:原始状态，黄色和蓝色不透明度设置为 0%

对此:

图 2:最终状态，黄色和蓝色不透明度设置为 100%

正如您所看到的，黄色和蓝色矩形不仅与红色矩形(屏幕表面)混合，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

如果你想混合不同的图层，那么你必须创建不同的 pygame.Surface s 或图像。可以通过加载图像 ( pygame.image ) 或构建 pygame.Surface 来生成 Surface对象。

创建一个完全透明的表面表面，每个像素都有 alpha 值。使用pygame.Surface.convert_alpha更改图像的像素格式，包括每个像素的 alpha。用透明颜色填充表面(例如pygame.Color(0, 0, 0, 0)):

<小时/>

最小示例:

import pygame

pygame.init()
clock = pygame.time.Clock()
screen = pygame.display.set_mode((600, 600), 0, 32)

def transparentSurface(size):
    surface = pygame.Surface(size).convert_alpha()
    surface.fill((0, 0, 0, 0))
    return surface

alpha, increase = 0, 1
run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    screen.fill(pygame.Color(247, 25, 0,255))
    
    alpha_surface1 = transparentSurface(screen.get_size())
    pygame.draw.rect(alpha_surface1, (247, 137, 0, 255), (120, 120, 480, 480))

    alpha_surface2 =  transparentSurface(screen.get_size())
    pygame.draw.rect(alpha_surface2, (220, 247, 0, alpha), (240, 240, 360, 360))

    alpha_surface3 =  transparentSurface(screen.get_size())
    pygame.draw.rect(alpha_surface3, (0, 247, 4), (360, 360, 240, 240) )

    alpha_surface4 =  transparentSurface(screen.get_size())
    pygame.draw.rect(alpha_surface4, (0, 78, 247, alpha), (480, 480, 120, 120) )
    
    screen.blit(alpha_surface1, (0,0))
    screen.blit(alpha_surface2, (0,0))
    screen.blit(alpha_surface3, (0,0))
    screen.blit(alpha_surface4, (0,0))

    pygame.display.update()
    
    alpha += increase
    if alpha < 0 or alpha > 255:
        increase *= -1
        alpha = max(0, min(255, alpha))

pygame.quit()