为什么在下面的Pymunk示例中物理学是错误的？
from __future__ import print_function
import sys
from math import pi
import pygame
from pygame.locals import USEREVENT, QUIT, KEYDOWN, KEYUP, K_s, K_r, K_q, K_ESCAPE, K_UP, K_DOWN, K_LEFT, K_RIGHT
from pygame.color import THECOLORS
import pymunk
from pymunk import Vec2d
import pymunk.pygame_util
LEG_GROUP = 1
class Simulator(object):
def __init__(self):
self.display_flags = 0
self.display_size = (600, 600)
self.space = pymunk.Space()
self.space.gravity = (0.0, -1900.0)
self.space.damping = 0.999 # to prevent it from blowing up.
# Pymunk physics coordinates start from the lower right-hand corner of the screen.
self.ground_y = 100
ground = pymunk.Segment(self.space.static_body, (5, self.ground_y), (595, self.ground_y), 1.0)
ground.friction = 1.0
self.space.add(ground)
self.screen = None
self.draw_options = None
def reset_bodies(self):
for body in self.space.bodies:
if not hasattr(body, 'start_position'):
continue
body.position = Vec2d(body.start_position)
body.force = 0, 0
body.torque = 0
body.velocity = 0, 0
body.angular_velocity = 0
body.angle = body.start_angle
def draw(self):
### Clear the screen
self.screen.fill(THECOLORS["white"])
### Draw space
self.space.debug_draw(self.draw_options)
### All done, lets flip the display
pygame.display.flip()
def main(self):
pygame.init()
self.screen = pygame.display.set_mode(self.display_size, self.display_flags)
width, height = self.screen.get_size()
self.draw_options = pymunk.pygame_util.DrawOptions(self.screen)
def to_pygame(p):
"""Small hack to convert pymunk to pygame coordinates"""
return int(p.x), int(-p.y+height)
def from_pygame(p):
return to_pygame(p)
clock = pygame.time.Clock()
running = True
font = pygame.font.Font(None, 16)
# Create the torso box.
box_width = 50
box_height = 100
# leg_length = 100
leg_length = 125
leg_thickness = 2
leg_shape_filter = pymunk.ShapeFilter(group=LEG_GROUP)
# Create torso.
mass = 200
points = [(-box_width/2, -box_height/2), (-box_width/2, box_height/2), (box_width/2, box_height/2), (box_width/2, -box_height/2)]
moment = pymunk.moment_for_poly(mass, points)
body1 = pymunk.Body(mass, moment)
body1.position = (self.display_size[0]/2, self.ground_y+box_height/2+leg_length)
body1.start_position = Vec2d(body1.position)
body1.start_angle = body1.angle
shape1 = pymunk.Poly(body1, points)
shape1.filter = leg_shape_filter
shape1.friction = 0.8
shape1.elasticity = 0.0
self.space.add(body1, shape1)
# Create leg extending from the right to the origin.
mass = 10
points = [
(leg_thickness/2, -leg_length/2),
(-leg_thickness/2, -leg_length/2),
(-leg_thickness/2, leg_length/2),
(leg_thickness/2, leg_length/2)
]
moment = pymunk.moment_for_poly(mass, points)
body2 = pymunk.Body(mass, moment)
body2.position = (self.display_size[0]/2-box_width/2+leg_thickness/2, self.ground_y+leg_length/2)
body2.start_position = Vec2d(body2.position)
body2.start_angle = body2.angle
shape2 = pymunk.Poly(body2, points)
shape2.filter = leg_shape_filter
shape2.friction = 0.8
shape2.elasticity = 0.0
self.space.add(body2, shape2)
# Link bars together at end.
pj = pymunk.PivotJoint(body1, body2, (self.display_size[0]/2-box_width/2, self.ground_y+leg_length))
self.space.add(pj)
# Attach the foot to the ground in a fixed position.
# We raise it above by the thickness of the leg to simulate a ball-foot. Otherwise, the default box foot creates discontinuities.
pj = pymunk.PivotJoint(self.space.static_body, body2, (self.display_size[0]/2-box_width/2, self.ground_y+leg_thickness))
self.space.add(pj)
# Actuate the bars via a motor.
motor_joint = pymunk.SimpleMotor(body1, body2, 0)
motor_joint.max_force = 1e10 # mimicks default infinity
# motor_joint.max_force = 1e9
# motor_joint.max_force = 1e7 # too weak, almost no movement
self.space.add(motor_joint)
# Add hard stops to leg pivot so the leg can't rotate through the torso.
hip_limit_joint = pymunk.RotaryLimitJoint(body1, body2, -pi/4., pi/4.) # -45deg:+45deg
self.space.add(hip_limit_joint)
last_body1_pos = None
last_body1_vel = None
simulate = False
while running:
# print('angles:', body1.angle, body2.angle)
# print('torso force:', body1.force)
print('body1.position: %.02f %.02f' % (body1.position.x, body1.position.y))
current_body1_vel = None
if last_body1_pos:
current_body1_vel = body1.position - last_body1_pos
print('current_body1_vel: %.02f %.02f' % (current_body1_vel.x, current_body1_vel.y))
current_body1_accel = None
if last_body1_vel:
current_body1_accel = current_body1_vel - last_body1_vel
print('current_body1_accel: %.02f %.02f' % (current_body1_accel.x, current_body1_accel.y))
servo_angle = (body1.angle - body2.angle) * 180/pi # 0 degrees means leg is angled straight down
servo_cw_enabled = servo_angle > -45
servo_ccw_enabled = servo_angle < 45
for event in pygame.event.get():
if event.type == QUIT or (event.type == KEYDOWN and event.key in (K_q, K_ESCAPE)):
sys.exit(0)
elif event.type == KEYDOWN and event.key == K_s:
# Start/stop simulation.
simulate = not simulate
last_body1_pos = Vec2d(body1.position)
if current_body1_vel:
last_body1_vel = Vec2d(current_body1_vel)
self.draw()
### Update physics
fps = 50
iterations = 25
dt = 1.0/float(fps)/float(iterations)
if simulate:
for x in range(iterations): # 10 iterations to get a more stable simulation
self.space.step(dt)
pygame.display.flip()
clock.tick(fps)
if __name__ == '__main__':
sim = Simulator()
sim.main()
这将使盒子放在细腿顶部。支腿通过枢轴连接到盒子，并通过另一个枢轴连接到地面。但是，支腿以偏心的方式连接到盒子的左侧，因此重心不平衡。在现实世界中，此设置将导致该框向右倾斜。但是，当您运行此代码（并按“ s”开始）时，它将显示向左倾斜的框。为什么是这样？
我尝试过调整质量（盒子的质量高，腿的质量低），盒子的重心以及调整关节的附着点，但是似乎没有任何改变。我究竟做错了什么？
我想用它来模拟现实世界的现象，但是直到获得它来重现现实世界的现象之前，我还是被困住了。
最佳答案
似乎是因为腿部形状与底部地面形状发生了冲突。
使它们不发生碰撞的最简单方法是将它们分开一点。例如，使腿短一点，使其不触地。
另一个解决方案是像在其他问题中一样进行操作，而忽略腿与地面之间的碰撞。为此，您可以设置一个形状过滤器，但是由于您可能想防止盒子与腿碰撞，并且同时计算盒子和地面之间的碰撞，我认为您需要使用形状的类别/遮罩按此处记录进行过滤：http://www.pymunk.org/en/latest/pymunk.html#pymunk.ShapeFilter
关于python - 如何解决Pymunk中不平衡的下降运动学，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/49600583/