直接在pygame中修改Surface像素的alpha

Question

我在 PyGame 中有一个 Surface。我想直接修改像素的 alpha 值。我尝试过使用各种访问 alpha 值的方法，但它们似乎不起作用。

from screeninfo import get_monitors
import pygame, os, numpy.random, pygame.surfarray

pygame.init()
FPS = 60
CLOCK = pygame.time.Clock()
monitor_info = get_monitors()
x = 0
y = 0
width = monitor_info[0].width
height = monitor_info[0].height
if len(monitor_info) > 1:
    if monitor_info[0].x < 0:
        x = 0
    else:
        x = monitor_info[0].width
    width = monitor_info[1].width
    height = monitor_info[1].height

os.environ['SDL_VIDEO_WINDOW_POS'] = "{},0".format(x)
pygame.display.init()
pygame.mouse.set_visible(False)
screen_info = pygame.display.Info()
screen_size = width, height
base_screen = pygame.display.set_mode(screen_size, pygame.NOFRAME)
base_screen.fill([100, 100, 100])
board_size = (int(min(width, height)*0.75), int(min(width, height)*0.75))
surface = pygame.Surface(board_size, pygame.SRCALPHA)
surface.fill([255, 255, 255, 255])
base_screen.blit(surface, (0,0))
pygame.display.flip()
pixels = numpy.random.uniform(low=0, high=255, size=(board_size[0], board_size[1], 3))
transparency = numpy.random.uniform(low=0, high=255, size=board_size).astype('uint8')
while True:
    events = pygame.event.get()
    ms = CLOCK.tick(FPS)
    print('\r             {}                  '.format(ms), end='')
    # pygame.surfarray.blit_array(surface, pixels)
    aa = pygame.surfarray.pixels_alpha(surface)
    aa = numpy.random.uniform(low=0, high=255, size=board_size).astype('uint8')
    del aa
    # for i in range(board_size[0]):
    #     for j in range(board_size[1]):
    #         a = surface.get_at((i,j))
    #         a[3] = 0
    #         surface.set_at((i,j), a)
    base_screen.blit(surface, (0,0))
    pygame.display.flip()

我已经在循环中尝试了这两种方法（pixels_array 和 get_at/set_at），但都不起作用——图像只是保持白色（如果我将初始 alpha 设置为 0，它会保持透明）。有谁知道如何为 Surface 设置每个像素的 alpha 值？

Answer 1

我发现了你的问题！！看不到 alpha 的原因是：

a) 你首先将surface alpha 设置为255，surface.fill([255, 255, 255, 255])

b) 我相信 aa = pygame.surfarray.pixels_alpha(surface) aa = numpy.random.uniform(low=0, high=255, size=board_size).astype('uint8') 不工作，但是 pygame.surfarray.blit_array(surface, pixels) 工作（产生颜色）但我不认为他们有任何实际的 Alpha。

c) 你需要填充 base_screen 并 THEN 让你的表面出现。如此常见的错误，但这是主要问题。

最后，Tim Robert 对 for 循环的评论，肯定会让你获得你的 alpha！

这是重新编写的工作（没有screeninfo，因为我目前没有那个库）：

import pygame, os, numpy.random, pygame.surfarray
from random import randint

pygame.init()
FPS = 60
CLOCK = pygame.time.Clock()
x = 50
y = 50
width = 500
height = 500

os.environ['SDL_VIDEO_WINDOW_POS'] = "{},0".format(x)
#pygame.display.init(), don't actually need this
pygame.mouse.set_visible(False)
screen_info = pygame.display.Info()
screen_size = width, height
base_screen = pygame.display.set_mode(screen_size, pygame.NOFRAME)
base_screen.fill([100, 100, 100])
board_size = (int(min(width, height)*0.75), int(min(width, height)*0.75))
surface = pygame.Surface(board_size, pygame.SRCALPHA)
surface.fill([255, 0, 0]) ###could also be surface.fill([255,0,0,255]) to set the whole surface's alpha straight up if you didn't want to change each pixel later

while True:
    #just so you can quit this program
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            raise SystemExit()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_q:
                pygame.quit()
                raise SystemExit()
                
    ms = CLOCK.tick(FPS)

    for i in range(board_size[0]):
         for j in range(board_size[1]):
             a = surface.get_at((i,j))
             a[3] = randint(0, 128)#OR SET TO REQUIRED ALPHA VALUE
             surface.set_at((i,j), a)

    ##################################################
    base_screen.fill([100, 100, 100]) #NEED TO DO THIS
    ##################################################

    base_screen.blit(surface, (0,0))
    pygame.display.flip()

（顺便说一句，我使用红色作为第二个表面颜色，因为我认为它会更突出）

编辑

正如 cmets 中所说的 Eternal Ambiguity，这里是更快的版本，much 代替 for 循环：

aa = pygame.surfarray.pixels_alpha(surface)
aa[:] = numpy.random.uniform(low=0, high=255, size=board_size).astype('uint8')
del aa

Answer 2

pygame.Surface.blit() 不会将目标表面中的像素替换为源表面。它混合（混合）表面的像素。实际上，您每帧都在将新表面与旧的先前表面混合。这意味着表面区域在几毫秒内呈现出均匀的颜色。您必须在每一帧中清除屏幕：

while True:
    # [...]

    base_screen.fill((0, 0, 0))
    base_screen.blit(surface, (0,0))
    pygame.display.flip()

---

小例子：

import pygame

pygame.init()

width, height = 200, 200
base_screen = pygame.display.set_mode((width, height))
clock = pygame.time.Clock()

board_size = (int(min(width, height)*0.75), int(min(width, height)*0.75))
surface = pygame.Surface(board_size, pygame.SRCALPHA)
surface.fill([255, 0, 0])

for x in range(board_size[0]):
    for y in range(board_size[1]):
        a = surface.get_at((x, y))
        a[3] = round(y / board_size[1] * 255)
        surface.set_at((x, y), a)

run = True
while run:
    clock.tick(100)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
                
    base_screen.fill((100, 100, 100))
    base_screen.blit(surface, surface.get_rect(center = base_screen.get_rect().center))
    pygame.display.flip()