python - Pygame，如何在屏幕上绘制形状并删除之前的表面？

Question

所以我有这段代码，它可以正常工作。我想要它做的是按不同的数量随机缩放正方形，它确实这样做了。我的问题在于 blit 函数，我的正方形似乎只是按比例放大，因为 blit 不会删除旧形状，它只是将新形状复制到表面。

如何使形状扩大和缩小，而不仅仅是扩大？

我的代码:

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

pygame.init()

w = 640
h = 480

screen = pygame.display.set_mode((w,h))
morphingShape = pygame.Surface((20,20))
morphingShape.fill((255, 137, 0)) #random colour for testing
morphingRect = morphingShape.get_rect()

def ShapeSizeChange(shape, screen):
    x = random.randint(-21, 20)
    w = shape.get_width()
    h = shape.get_height()
    if w + x > 0 and h + x > 0:
        shape = pygame.transform.smoothscale(shape, (w + x, h + x))
    else:
        shape = pygame.transform.smoothscale(shape, (w - x, h - x))
    shape.fill((255, 137, 0))
    rect = shape.get_rect()
    screen.blit(shape, rect)
    return shape


while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()
    morphingShape = ShapeSizeChange(morphingShape, screen)
    pygame.display.update()

Answer 1

在每一帧(While 循环的每次迭代)你都应该删除屏幕。默认情况下，屏幕(窗口)颜色为黑色，因此您应该通过调用 screen.fill( (0,0,0) ) 清除屏幕。下面是完整的代码，现在可以正常工作了:

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

pygame.init()

w = 640
h = 480

screen = pygame.display.set_mode((w,h))
morphingShape = pygame.Surface((20,20))
morphingShape.fill((255, 137, 0)) #random colour for testing
morphingRect = morphingShape.get_rect()

# clock object that will be used to make the animation
# have the same speed on all machines regardless
# of the actual machine speed.
clock = pygame.time.Clock()

def ShapeSizeChange(shape, screen):
    x = random.randint(-21, 20)
    w = shape.get_width()
    h = shape.get_height()
    if w + x > 0 and h + x > 0:
        shape = pygame.transform.smoothscale(shape, (w + x, h + x))
    else:
        shape = pygame.transform.smoothscale(shape, (w - x, h - x))
    shape.fill((255, 137, 0))
    rect = shape.get_rect()
    screen.blit(shape, rect)
    return shape


while True:
    # limit the demo to 50 frames per second
    clock.tick( 50 );

    # clear screen with black color
    # THIS IS WHAT WAS REALLY MISSING...
    screen.fill( (0,0,0) )

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()
    morphingShape = ShapeSizeChange(morphingShape, screen)
    pygame.display.update()

请注意，只需添加 screen.fill( (0,0,0) ) 即可解决您的问题。