Pygame，如何在屏幕上绘制一个形状并删除以前的表面？答案

【问题标题】：Pygame, how to draw a shape to the screen and delete the previous surface?Pygame，如何在屏幕上绘制一个形状并删除以前的表面？
【发布时间】：2012-07-30 19:41:51
【问题描述】：

所以我有这个代码，它做了它应该做的事。我想要它做的是将正方形随机缩放不同的数量，它确实如此。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()

【问题讨论】：

标签： python python-3.x pygame

【解决方案1】：

在每一帧（While 循环的每次迭代）上，您都应该擦除屏幕。默认情况下屏幕（窗口）颜色为黑色，因此您应该调用screen.fill( (0,0,0) ) 清除屏幕。下面是完整的代码，现在可以按预期工作了：

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。

【讨论】：