Parallel getCameraImage from a physics client

[gliese581gg]

I am trying to use multiprocessing to get images from multiple positions in the same simulation instance in parallel.

It seems like following example works :

import numpy as np
import pybullet as pb
import pybullet_data
import cv2
import multiprocessing as mp
import time



# Works only if
#   num_process = 1 and pb.GUI_SERVER
#   num_process  > 1 and pb.DIRECT
num_process = 5
conn = pb.connect( pb.DIRECT  )

print(conn)
pb.setAdditionalSearchPath(pybullet_data.getDataPath())


r2d2_id = pb.loadURDF("r2d2.urdf", [0, 0, 0])
r2d22_id = pb.loadURDF("r2d2.urdf", [1, 1, 0])
width = 640
height = 480

fov = 60
aspect = width / height
near = 0.02
far = 10

angle = 0

print(conn,r2d2_id,r2d22_id)


def capture(i,x,y):
    view_matrix = pb.computeViewMatrix([x, y, 4], [0, 0, 0], [1, 0, 0])
    projection_matrix = pb.computeProjectionMatrixFOV(fov, aspect, near, far)

    # Get depth values using the OpenGL renderer
    tt = time.time()
    images = pb.getCameraImage(width,
                              height,
                              view_matrix,
                              projection_matrix,
                              shadow=True,
                              renderer=pb.ER_BULLET_HARDWARE_OPENGL)
    print(i,time.time()-tt)
    rgb_opengl = np.reshape(images[2], (height, width, 4))
    cv2.imwrite('rgb%d.jpg'%i,rgb_opengl[:,:,:3])
    #cv2.imshow('rgb%d'%i,rgb_opengl[:,:,:3])

    return True


def capture_loop(i):
    x = i * 0.5
    y = i * 0.5
    while True:
        capture(i,x,y)

angle = 0
procs = []
for i in range(num_process):
    p = mp.Process( target=capture_loop, args=(i,))
    p.daemon = True
    p.start()
    procs.append(p)

while True:
    '''
    procs = []
    for i in range(num_process):
        x = i * 0.5
        y = i * 0.5
        #capture(i,x,y)
        p = mp.Process( target=capture, args=(i,x,y,))
        p.start()
        procs.append(p)

    for p in procs:
        p.join()
    '''
    pos = [0,0,0]
    angle_rad = np.pi*0.05*angle
    if angle_rad > np.pi : angle_rad -= 2*np.pi
    euler = [0,0,np.pi*0.05*angle]
    quat = pb.getQuaternionFromEuler(euler)
    pb.resetBasePositionAndOrientation(r2d2_id,pos,quat)
    pb.stepSimulation()
    angle += 1

However, I am not sure whether this is the right way to do it.

Moreover, I cannot use the debug renderer with parallel getCameraImage

Is there a better way to get multiple camera images in parallel?

Can anyone explain why the above setting works and others don't?