这节我们研究下pygame的几种碰撞检测模式:
如上图,左侧是默认的检测模式:基于矩形的检测(这也是性能最好的模式), 右侧是基于圆形的检测(性能略差于矩形检测)。
矩形检测法虽然性能好,但是缺点也很明显:检测不准确,上图中"飞机与目标"从视觉上看,根本没碰到。
为了改进,pygame给这二种模式,新增了xxx_ratio的方法,允许指定检测时,指定二个目标的叠加程度,只有达到指定的叠加值,才认为是真正碰撞到了,参考下图:
注:ratio的值越大,表示叠加的部分越少!
我们写一个小程序来测试一下:
1 import pygame
2 from os import path
3 from xml.dom.minidom import parse
4
5 SIZE = (WIDTH, HEIGHT) = (265, 320)
6 FPS = 45
7
8 BLACK = 0, 0, 0
9 WHITE = 255, 255, 255
10
11 pygame.init()
12 pygame.mixer.init()
13
14 screen = pygame.display.set_mode(SIZE)
15 pygame.display.set_caption("My Game")
16 clock = pygame.time.Clock()
17
18 spritesheet_image_file_name = path.join(path.dirname(__file__), "../img/spritesheet_jumper.png")
19 spritesheet_xml_file_name = path.join(path.dirname(__file__), "../img/spritesheet_jumper.xml")
20 spritesheet_image = pygame.image.load(spritesheet_image_file_name)
21 spritesheet_image.set_colorkey(BLACK)
22 spritesheet_dom_tree = parse(spritesheet_xml_file_name)
23 root_textures = spritesheet_dom_tree.documentElement
24 sub_textures = root_textures.getElementsByTagName("SubTexture")
25 dic_image = {}
26
27
28 def get_image_rect(img_name):
29 if dic_image.get(img_name):
30 return dic_image[img_name]
31 for texture in sub_textures:
32 name = texture.getAttribute("name")
33 if img_name == name:
34 dic_image[img_name] = pygame.Rect(
35 int(texture.getAttribute("x")),
36 int(texture.getAttribute("y")),
37 int(texture.getAttribute("width")),
38 int(texture.getAttribute("height"))
39 )
40 return dic_image[img_name]
41
42
43 def get_image(img_name):
44 rect = get_image_rect(img_name);
45 image = pygame.Surface((rect.width, rect.height))
46 image.blit(spritesheet_image, (0, 0), rect)
47 image.set_colorkey(BLACK)
48 return image
49
50
51 class Demo(pygame.sprite.Sprite):
52 def __init__(self, image, pos):
53 pygame.sprite.Sprite.__init__(self)
54 self.image = image
55 self.rect = self.image.get_rect()
56 self.rect.x = pos[0]
57 self.rect.y = pos[1]
58
59
60 running = True
61 pos1 = (20, 5)
62 pos2 = (125, 110)
63
64 demo1 = Demo(get_image("bunny1_walk1.png"), pos1)
65 demo2 = Demo(get_image("bunny2_stand.png"), pos2)
66
67 all_sprites = pygame.sprite.LayeredUpdates()
68 all_sprites.add(demo1, layer=2)
69 all_sprites.add(demo2, layer=1)
70
71 group2 = pygame.sprite.Group()
72 group2.add(demo2)
73
74 while running:
75 clock.tick(FPS)
76
77 for event in pygame.event.get():
78 if event.type == pygame.QUIT:
79 running = False
80 if event.type == pygame.KEYDOWN:
81 if event.key == pygame.K_LEFT:
82 demo1.rect.x += -3
83 if event.key == pygame.K_RIGHT:
84 demo1.rect.x += 3
85 if event.key == pygame.K_UP:
86 demo1.rect.y += -3
87 if event.key == pygame.K_DOWN:
88 demo1.rect.y += 3
89
90 screen.fill(BLACK)
91
92 all_sprites.draw(screen)
93
94 pygame.draw.rect(screen, (0, 255, 0), demo2.rect, 1)
95 pygame.draw.rect(screen, (255, 0, 0), demo1.rect, 1)
96
97 font = pygame.font.SysFont("Menlo", 25, True)
98
99 # 默认的检测模式(rect)
100 if pygame.sprite.spritecollide(demo1, group2, False):
101 pos_txt = font.render("hit:true", 1, (255, 255, 128))
102 else:
103 pos_txt = font.render("hit:false", 1, (255, 255, 128))
104 screen.blit(pos_txt, (150, 10))
105
106 pygame.display.update()
107
108 pygame.quit()
这是默认的Rect检测模式。把100行换成:
# 矩形检测(至少要重叠1-0.7=30%才算发生了碰撞)
if pygame.sprite.spritecollide(demo1, group2, False, pygame.sprite.collide_rect_ratio(0.7)):
再看下效果:
继续,换成圆形检测试下:
# 圆形检测(至少要重叠1-0.7=30%才算发生了碰撞)
if pygame.sprite.spritecollide(demo1, group2, False, pygame.sprite.collide_circle_ratio(0.7)):
那么,有没有一种方法能做到精确检测呢?当然有,有一种基于mask(在绘图软件中,也称为遮罩或蒙版)的检测方法,类似把背景去掉后,像素级的碰撞检测,当然性能也是最差的。
首先要在Sprite的类上,指定mask:
1 class Demo(pygame.sprite.Sprite):
2 def __init__(self, image, pos):
3 pygame.sprite.Sprite.__init__(self)
4 self.image = image
5 self.rect = self.image.get_rect()
6 self.rect.x = pos[0]
7 self.rect.y = pos[1]
8 #指定蒙版
9 self.mask = pygame.mask.from_surface(self.image)
然后把检测代码改成:
# 基于mask的检测
if pygame.sprite.spritecollide(demo1, group2, False, pygame.sprite.collide_mask):
好了,利用上面学到的知识,把上节的遗留问题:"player与enemy的碰撞检测不准确" 解决一下,效果如下:
优化前 | 优化后 |
---|---|
| |
源码示例:https://github.com/yjmyzz/kids-can-code/tree/master/part_17