Visualizing multiple pyBullet server instances

[manas96]

Hi, I'd like to spawn multiple instances of the physics server, send them some geometry, start them and then combine their output in a single GUI window. I'm trying to repurpose the existing 3D rendering infrastructure that pyBullet provides. Here's what I'm trying to do so far:

p0 = bc.BulletClient(connection_mode=pybullet.DIRECT)
p1 = bc.BulletClient(connection_mode=pybullet.DIRECT)
p0.loadURDF("r2d2.urdf")
p1.loadSDF("stadium.sdf")

# This will be used to render the output from p0 and p1 both
pgui = bc.BulletClient(connection_mode=pybullet.GUI)

while 1:
    p0.stepSimulation()
    p1.stepSimulation()

    # somehow get all geometry information
    geom0 = p0.getGeom()
    geom1 = p1.getGeom()
    # send all geometry to pgui and render it
    pgui.send(geom0, geom1)

I'm currently looking into the saveState() and restoreState() methods to do this but this feels very hacky, so my question is is there a better way to do this? Note that the geometry on both "worker" servers might not be the same.

Edit Here's the code I'm trying to work with:

import pybullet_utils.bullet_client as bc
import pybullet as p
import pybullet_data
import time
STATE_FILE = 'state.bullet'
SCENE_FILE = 'scenes/spiralWall.bullet'

def setupServer(handle):
    handle.setAdditionalSearchPath(pybullet_data.getDataPath())
    handle.setPhysicsEngineParameter(deterministicOverlappingPairs=1)

    startOrientation = handle.getQuaternionFromEuler([0, 0, 0])
    handle.loadURDF("r2d2.urdf", [0, 0, 1], startOrientation)
    handle.loadURDF("plane.urdf")
    handle.setGravity(0, 0, -10)

p1 = bc.BulletClient(connection_mode=p.DIRECT)
setupServer(p1)

pgui = bc.BulletClient(connection_mode=p.GUI)
#setupServer(pgui)

while 1:
    p1.stepSimulation()

    p1.saveBullet(STATE_FILE)
    pgui.restoreState(fileName=STATE_FILE)

    pgui.stepSimulation()

    time.sleep(1. / 240.)

Which gives me the error:

Traceback (most recent call last):
  File "C:\Users\m84241864\Desktop\projects\bullet\python\multi_server.py", line 43, in <module>
    pgui.restoreState(fileName=STATE_FILE)
pybullet.error: Couldn't restore state.

I am able to restore p1's state in pgui if I uncomment #setupServer(pgui). But I would like to be able to restore geometry that is previously unknown to pgui. Also, how do I debug pybullet.error's?

[manas96]

I was able to hack something together by maintaining two copies of geometry objects. That is, if we have geometries {X,Y} on p1, {A,B} on p2, I maintain geometries {X,Y,A,B} on the GUI server and update their positions every frame. But happy to hear if there is a cleaner solution.

[yogha001]

Hi @manas96, I am currently working on the same issue and I was wondering if you have found a solution for it since then? Or @erwincoumans could you help us ?

[manas96]

Hi @yogha001, I ended up building on top of the workaround I posted above.

[yogha001]

Hi @manas96, so happy you replied. Well i'm not really working on excatly the same issue. Here is the issue I'm working on, just made a post: https://github.com/bulletphysics/bullet3/issues/4402