pendulum.py

# pyODE example 2: Connecting bodies with joints

import pygame
from pygame.locals import *
import ode


def coord(x,y):
    "Convert world coordinates to pixel coordinates."
    return int(320+170*x), int(400-170*y)


# Initialize pygame
pygame.init()

# Open a display
srf = pygame.display.set_mode((640,480))

# Create a world object
world = ode.World()
world.setGravity((0,-9.81,0))

# Create two bodies
body1 = ode.Body(world)
M = ode.Mass()
M.setSphere(2500, 0.05)
body1.setMass(M)
body1.setPosition((1,2,0))

body2 = ode.Body(world)
M = ode.Mass()
M.setSphere(2500, 0.05)
body2.setMass(M)
body2.setPosition((2,2,0))

# Connect body1 with the static environment
j1 = ode.BallJoint(world)
j1.attach(body1, ode.environment)
j1.setAnchor( (0,2,0) )

# Connect body2 with body1
j2 = ode.BallJoint(world)
j2.attach(body1, body2)
j2.setAnchor( (1,2,0) )


# Simulation loop...

fps = 50
dt = 1.0/fps
loopFlag = True
clk = pygame.time.Clock()

while loopFlag:
    events = pygame.event.get()
    for e in events:
        if e.type==QUIT:
            loopFlag=False
        if e.type==KEYDOWN:
            loopFlag=False

    # Clear the screen
    srf.fill((255,255,255))

    # Draw the two bodies
    x1,y1,z1 = body1.getPosition()
    x2,y2,z2 = body2.getPosition()
    pygame.draw.circle(srf, (55,0,200), coord(x1,y1), 20, 0)
    pygame.draw.line(srf, (55,0,200), coord(0,2), coord(x1,y1), 2)
    pygame.draw.circle(srf, (55,0,200), coord(x2,y2), 20, 0)
    pygame.draw.line(srf, (55,0,200), coord(x1,y1), coord(x2,y2), 2)

    pygame.display.flip()

    # Next simulation step
    world.step(dt)

    # Try to keep the specified framerate
    clk.tick(fps)