Pygame中如何调整旋转矩形的尺寸使其小于关联图片大小

问题原因 #

Pygame的Rect对象所有坐标、尺寸属性是联动的：当你修改topleft属性后，Rect的宽度会自动变化，此时再修改topright属性会直接覆盖上一步的调整，最终尺寸会回弹到和原图一致的初始值，所以修改不生效。

解决方法 #

不要通过修改两个顶点的方式调整矩形尺寸，先直接修改Rect的宽高参数，再对齐中心即可。你可以把内边距做成可配置的参数，灵活调整矩形的缩小幅度。

修正后的核心函数 #

def draw_rect_angle(surf, rect, pivot, angle, padding=25):   
    # 先缩小矩形尺寸，padding是四周向内缩的距离
    shrinked_rect = pygame.Rect(
        rect.left + padding,
        rect.top + padding,
        rect.width - padding * 2,
        rect.height - padding * 2
    )
    # 再取四个顶点做旋转计算
    pts = [shrinked_rect.topleft, shrinked_rect.topright, shrinked_rect.bottomright, shrinked_rect.bottomleft]
    pts = [(pygame.math.Vector2(p) - pivot).rotate(-angle) + pivot for p in pts]
    pygame.draw.lines(surf, (255, 255, 0), True, pts, 3)

调用说明 #

调用函数时可以自定义padding参数调整缩进幅度，不传则默认使用25的缩进值：

# 主循环内调用示例，设置30像素缩进
draw_rect_angle(screen, rect, screen_center, angle, padding=30)

完整可运行代码 #

import pygame

pygame.init()
screen = pygame.display.set_mode((400, 400))
font = pygame.font.SysFont(None, 50)
clock = pygame.time.Clock()

#orig_image = font.render("rotated rectangle", True, (255, 0, 0))
angle =0
orig_image = pygame.image.load("Bilder/baum2.png")
rotated_image = pygame.transform.rotate(orig_image, angle)

def draw_rect_angle(surf, rect, pivot, angle, padding=25):   
    shrinked_rect = pygame.Rect(
        rect.left + padding,
        rect.top + padding,
        rect.width - padding * 2,
        rect.height - padding * 2
    )
    pts = [shrinked_rect.topleft, shrinked_rect.topright, shrinked_rect.bottomright, shrinked_rect.bottomleft]
    pts = [(pygame.math.Vector2(p) - pivot).rotate(-angle) + pivot for p in pts]
    pygame.draw.lines(surf, (255, 255, 0), True, pts, 3)

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

    screen.fill(0)
    screen_center = screen.get_rect().center
    screen.blit(rotated_image, rotated_image.get_rect(center = screen_center))
    rect = orig_image.get_rect(center = screen_center)
    draw_rect_angle(screen, rect, screen_center, angle)
    pygame.display.flip()

pygame.quit()
exit()

内容的提问来源于stack exchange，提问作者Joachim