pygame.surface.get_at((x，y))未返回正确的像素数据

Question

我有一个简单的程序，它允许用户在黑框中绘制白色像素。当用户单击蓝色按钮时，我希望我的程序遍历绘制框中的所有像素并将像素数据添加到数组中以供以后在另一个项目中使用。然而，即使用户在那里绘制了图像，它也只会为每个像素返回黑色。

import pygame
from pygame.locals import *
import sys

# set up the screen
pygame.init()
screen = pygame.display.set_mode((200, 200))
pygame.display.set_caption("drawTest")
clock = pygame.time.Clock()

# goes through the screen data and reads the pixel data
def GetPixelDataOfDrawScreen():
    for i in range(200):
        for j in range(200):
            if(i > 49 and i < 150):
                if(j > 49 and j < 150):

                    # gets the red, green, blue and alpha (RGBA) components of the pixel
                    pixelColor = screen.get_at((i, j))
                    print(i, pixelColor[0])

                    if(pixelColor[0] == 255):
                        pixelDataOfDrawBox.append(255)
                    else:
                        pixelDataOfDrawBox.append(0)

                    # dosen't work
    print(pixelDataOfDrawBox)

pixelDataOfDrawBox = []
rects = []

while True:

    for event in pygame.event.get(): 
            if event.type == pygame.QUIT: # adds close button to screen
                sys.exit()

    screen.fill((255, 255, 255))                                                    

    # gets the mouse position
    mouseX, mouseY = pygame.mouse.get_pos()

    # draw drawing box
    boxX = 50
    boxY = 50
    pygame.draw.rect(screen, (0, 0, 0), (boxX, boxY, 100, 100))

    if(mouseX >= boxX and mouseX <= boxX + 100 - 2): # check if drawing
        if(mouseY >= boxY and mouseY <= boxY + 100 - 2):
            if(pygame.mouse.get_pressed()[0]):
                rects.append([mouseX, mouseY, 2, 2])

    # blue button
    bButtonX = 100
    bButtonY = 150
    pygame.draw.rect(screen, (0, 0, 255), (bButtonX, bButtonY, 50, 20))

    if(mouseX >= bButtonX and mouseX <= bButtonX + 50): # check if pressed
        if(mouseY >= bButtonY and mouseY <= bButtonY + 20):
            pygame.draw.rect(screen, (0, 0, 180), (bButtonX, bButtonY, 50, 20))
            if(pygame.mouse.get_pressed()[0]):
                GetPixelDataOfDrawScreen()

    # red button
    rButtonX = 50
    rButtonY = 150
    pygame.draw.rect(screen, (255, 0, 0), (rButtonX, rButtonY, 50, 20))

    if(mouseX >= rButtonX and mouseX <= rButtonX + 50):
        if(mouseY >= rButtonY and mouseY <= rButtonY + 20):
            pygame.draw.rect(screen, (180, 0, 0), (rButtonX, rButtonY, 50, 20))

    # draw the rects
    for r in rects:
        pygame.draw.rect(screen, (255, 255, 255), (r[0], r[1], r[2], r[3]))

    pygame.display.flip()
    clock.tick(60)

Answer 1

问题在于，在清除＜code＞屏幕＜/code＞表面之后，在绘制白色矩形/像素之前，检查像素。此时绘图框区域仍为黑色。快速修复方法是在绘制矩形的代码下面调用GetPixelDataOfDrawScreen：

# draw the rects
for r in rects:
    pygame.draw.rect(screen, (255, 255, 255), (r[0], r[1], r[2], r[3]))

if(mouseX >= bButtonX and mouseX <= bButtonX + 50): # check if pressed
    if(mouseY >= bButtonY and mouseY <= bButtonY + 20):
        pygame.draw.rect(screen, (0, 0, 180), (bButtonX, bButtonY, 50, 20))
        if(pygame.mouse.get_pressed()[0]):
            GetPixelDataOfDrawScreen()

pygame.display.flip()
clock.tick(60)

此外，程序也可以简化。您可能只需使用＜code＞json＜/code＞或＜code＞pickle＜/code＞模块序列化＜code＞rects＜/code＞列表，或者为绘图区域创建一个单独的曲面，然后只需将其保存为＜code＞pygame.image.save＜/code＞。

这里有一个例子，我在另一个表面而不是屏幕上画画。可以用< code>pygame.image.save保存，用< code>pygame.image.load加载(按< kbd>S和< kbd>O)。我还推荐创建< code>pygame。Rect对象，因为它们有有用的碰撞检测方法，如< code>collidepoint:

import sys
import pygame


pygame.init()
screen = pygame.display.set_mode((200, 200))
clock = pygame.time.Clock()

box_surface = pygame.Surface((100, 100))
box = box_surface.get_rect(topleft=(50, 50))
blue_button = pygame.Rect(100, 150, 50, 20)
red_button = pygame.Rect(50, 150, 50, 20)

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()
        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_s:  # Press s to save the image.
                pygame.image.save(box_surface, 'box.png')
            elif event.key == pygame.K_o:  # Press o to load the image.
                box_surface = pygame.image.load('box.png').convert()

    mouse_pos = pygame.mouse.get_pos()
    if pygame.mouse.get_pressed()[0]:
        # Adjust the mouse positions because the box is positioned at (100, 100).
        mouse_x, mouse_y = mouse_pos[0]-box.x, mouse_pos[1]-box.y
        pygame.draw.rect(box_surface, (255, 255, 255), [mouse_x, mouse_y, 2, 2])

    # Draw everything.
    screen.fill((255, 255, 255))
    screen.blit(box_surface, box)
    pygame.draw.rect(screen, (0, 0, 255), blue_button)
    pygame.draw.rect(screen, (255, 0, 0), red_button)
    if red_button.collidepoint(mouse_pos):
        pygame.draw.rect(screen, (180, 0, 0), red_button)
    if blue_button.collidepoint(mouse_pos):
        pygame.draw.rect(screen, (0, 0, 180), blue_button)

    pygame.display.flip()
    clock.tick(60)