获取 pymunk 旋转动能体的更新坐标

Question

下面是一个旋转的动力皮蒙克物体，里面有一个质量。动画开始播放后，有没有办法获取“body_type”顶部水平部分的中点。最初，我感兴趣的动体上的点的坐标为 (400,500)。旋转开始后如何打印相关点的更新坐标

import pymunk

import pymunk.pygame_util

import pygame

GRAY = (220, 220, 220)

width_mass=50

height_mass=50

pygame.init()

size = 800,600

screen = pygame.display.set_mode(size)

draw_options = pymunk.pygame_util.DrawOptions(screen)

space = pymunk.Space()

space.gravity = (0,-50)

pts = [(-27, -238.5), (27,-238.5), (27,238.5), (-27,238.5)]

body_type=pymunk.Body(body_type=pymunk.Body.KINEMATIC)  

body_type.position = (400, 263.5)  

space.add(body_type)

for i in range(4):

    segment = pymunk.Segment(body_type, pts[i], pts[(i+1)%4], 2)

    segment.elasticity = 0

    segment.friction=0

    space.add(segment)

body_type.angular_velocity=1

body = pymunk.Body(mass=1, moment=100)

body.position = 400,400

mass = pymunk.Poly.create_box(body, (width_mass, height_mass))

mass.elasticity = 0

space.add(body, mass)

running = True

while running:

    for event in pygame.event.get():

        if event.type == pygame.QUIT:

            running = False

            #pygame.image.save(screen, 'intro1.png')

    screen.fill(GRAY)

    space.debug_draw(draw_options)

    pygame.display.update()

    space.step(0.01)

Answer 1

a 的当前位置Body存储在position属性中（例如space.bodies[0].position）。PyGame 使用左上角为 (0, 0) 的坐标系。y 轴需要反转 ( screen.get_height() - pos[1])，因为 y 轴一般指向上，但在 PyGame 坐标系中 y 轴指向下。running = Truewhile running:    # [...]    # draw a dot in at the center of the bodies    for body in space.bodies:        pos = body.position        pygame.draw.circle(screen, (255,0,0), (pos[0], screen.get_height()-pos[1]), 7)    pygame.display.update()    space.step(0.01)a 的当前角度Body存储在angle属性中（例如body_type.angle）。可以通过将旋转的相对位置与绝对位置相加来计算点的当前位置。旋转位置可以通过简单的三角函数计算：pos = abs_pos[0] + rel_dist * math.cos(angle), abs_pos[1] + rel_dist * math.sin(angle)首先，您必须根据相对笛卡尔坐标计算相对极坐标：rel_pos = (0, 238.5) rel_dist, rel_angle = math.hypot(*rel_pos), math.atan2(rel_pos[1], rel_pos[0])将当前角度添加到极坐标角度：angle = rel_angle + body_type.angle例如：running = Truewhile running:    # [...]    abs_pos = body_type.position    rel_pos = (0, 238.5)    rel_dist, rel_angle = math.hypot(*rel_pos), math.atan2(rel_pos[1], rel_pos[0])        angle = rel_angle + body_type.angle    pos = abs_pos[0] + rel_dist * math.cos(angle), abs_pos[1] + rel_dist * math.sin(angle)    pygame.draw.circle(screen, (255, 255, 0), (pos[0], screen.get_height() - pos[1]), 7)    pygame.display.update()    space.step(0.01)最小的例子：import pymunkimport pymunk.pygame_utilimport pygameimport mathGRAY = (220, 220, 220)width_mass=50height_mass=50pygame.init()size = 800,600screen = pygame.display.set_mode(size)draw_options = pymunk.pygame_util.DrawOptions(screen)space = pymunk.Space()space.gravity = (0,-50)pts = [(-27, -238.5), (27,-238.5), (27,238.5), (-27,238.5)]body_type=pymunk.Body(body_type=pymunk.Body.KINEMATIC)  body_type.position = (400, 263.5)  space.add(body_type)for i in range(4):    segment = pymunk.Segment(body_type, pts[i], pts[(i+1)%4], 2)    segment.elasticity = 0    segment.friction=0    space.add(segment)body_type.angular_velocity=0.5body = pymunk.Body(mass=1, moment=100)body.position = 400,400mass = pymunk.Poly.create_box(body, (width_mass, height_mass))mass.elasticity = 0space.add(body, mass)running = Truewhile running:    for event in pygame.event.get():        if event.type == pygame.QUIT:            running = False            #pygame.image.save(screen, 'intro1.png')    screen.fill(GRAY)    space.debug_draw(draw_options)    for body in space.bodies:        pos = body.position        pygame.draw.circle(screen, (255, 0, 0), (pos[0], screen.get_height() - pos[1]), 7)    abs_pos = body_type.position    rel_pos = (0, 238.5)    rel_dist, rel_angle = math.hypot(*rel_pos), math.atan2(rel_pos[1], rel_pos[0])    angle = rel_angle + body_type.angle    print( body_type.position.angle)    pos = abs_pos[0] + rel_dist * math.cos(angle), abs_pos[1] + rel_dist * math.sin(angle)    pygame.draw.circle(screen, (255, 255, 0), (pos[0], screen.get_height() - pos[1]), 7)    pygame.display.update()    space.step(0.01)

Answer 2

使 Pymunk 模拟的行为类似于本机 PyGame 坐标。您只需将以下行添加到您的代码中即可。pygame.pygame_util.positive_y_is_up = True自 PyMunk 6.0 起已默认为 True。