Real-Time Physics Simulation Forum

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-25T20:36:49+00:00

@Erwin: In case this comes in handy, I started making a wiki page stub based on what you posted here. This might be nice for the earlyadopters such as scropion81, me and such.

Here it is:
http://bulletphysics.org/mediawiki-1.5. ... g_pybullet

Some early feedback:

Your step-by-step guide worked well on Linux Mint here, I can see the Example Browser with a plane and a ball. However, the p.setSimulation() command does not exist (anymore?). What is the intention of it?

Statistics: Posted by benelot — Tue Oct 25, 2016 8:36 pm

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-16T17:52:05+00:00

Yes, in your case (and when using pybullet in a content creation environment such as Blender etc) programmatically creating shapes, rigid bodies and constraints make more sense.
Also, note that the OpenCL GPGPU rigid body pipeline hasn't been developed for many year, so it will take some time to get it into good shape again, and them putting it behind the abstract API.

I'll look into all of this, as part of my work.

Statistics: Posted by Erwin Coumans — Sun Oct 16, 2016 5:52 pm

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-15T21:28:08+00:00

Ok, and the hardcoded example works too.
Only thing what worries me a bit about loading from urdf is the short delay in loading time, even already in the example browser
Imagine i want to use dynamic voronoi fracturing. For this purpose in blender i let bullet fire contact callbacks to blender,
where the impact point and force is evaluated basically and a pointcloud for the next voronoi fracture of the existing
shards is generated. In the Fracture Modifier in blender this already works quite nicely. But if i constantly have to write and
read urdf files containing a new bigger set of shards, i expect this loading time to become slower and slower. This will be a serious
performance bottleneck and slow down the sim unnecessarily.

So i am looking forward on how to perhaps create rigidbodies and constraints too directly thru the C-API for Bullet 3.x.

scorpion81

Statistics: Posted by scorpion81 — Sat Oct 15, 2016 9:28 pm

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-15T20:09:40+00:00

You can also try out pybullet to connect to a 'physics server' in the example browser:

First start the example browser, and select the 'Experiments/Physics Server' example, and leave it running. Before running the script below, your ExampleBrowser in 'Experiments/Physics Server' should look similar to this:
physics_server512.png
In a new terminal, start python in the build_cmake/example/pybullet directory, start it (python) and then run the following script.
Code:
import pybullet as pp.connect(p.SHARED_MEMORY)p.setRealTimeSimulation(1)
The p.setRealTimeSImulation(1) will add some hard-coded world/objects (used for the VR demo). You can also leave out the 'p.setRealTimeSimulation(1)' command. In that case, you have to manually 'step' the simulation by sending 'p.stepSimulation' commands and put objecs in the world by using loadUrdf/loadSdf.

After running above script, it should look similar to this:
pybullet_sharedmem.png

Ok, i got the pybullet to run now. Had to recompile my static python 3.5 lib to a shared one, else i got the same linker error. (and i used Cmake and your instructions too)
Currently i am looking into pythons xml ElementTree on how to write urdf links (and joints later maybe) from the mesh shards as an XML file.
It would be even nicer if the Bullet C-API and thus pybullet would allow this in a more direct way, as you mentioned before
Will try your "hardcoded" example later.

Greetings, scorpion81

Statistics: Posted by scorpion81 — Sat Oct 15, 2016 8:09 pm

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-15T18:16:39+00:00

You can also try out pybullet to connect to a 'physics server' in the example browser:

First start the example browser, and select the 'Experiments/Physics Server' example, and leave it running. Before running the script below, your ExampleBrowser in 'Experiments/Physics Server' should look similar to this:

In a new terminal, start python in the build_cmake/example/pybullet directory, start it (python) and then run the following script.

Code:

import pybullet as pp.connect(p.SHARED_MEMORY)p.setRealTimeSimulation(1)

The p.setRealTimeSImulation(1) will add some hard-coded world/objects (used for the VR demo). You can also leave out the 'p.setRealTimeSimulation(1)' command. In that case, you have to manually 'step' the simulation by sending 'p.stepSimulation' commands and put objecs in the world by using loadUrdf/loadSdf.

After running above script, it should look similar to this:

Statistics: Posted by Erwin Coumans — Sat Oct 15, 2016 6:16 pm

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-15T18:04:22+00:00

Use cmake to build pybullet on Linux and Mac, there are some issues building pybullet using premake.
In the Bullet root directory:

edit build_and_run_cmake.sh and turn BUILD_PYBULLET=ON

then run this script
./build_and_run_cmake.sh
This should build all of Bullet and launch the ExampleBrowser. Play with this a bit, and exit it using key.

Then change directory to build_cmake/examples/pybullet. On Linux use

Code:

ln -s libpybullet.so pybullet.so

On Mac OSX use

Code:

ln -s libpybullet.dylib pybullet.so

Start python while in this directory, so it can find pybullet.so, and start your first script: (replace p.GUI with p.DIRECT or p.SHARED_MEMORY, -> shared memory will connect to example browser, while in 'experimental/physics server' mode)

Code:

import pybullet as pp.connect(p.GUI)p.loadURDF("plane.urdf")p.loadURDF("sphere_small.urdf",0,0,2)p.setSimulation()

The VR example only works on Windows at the moment (waiting for Valve/HTC Vive/Oculus Rift),
but you can see it using pybullet as follows:

Code:

import pybullet as pp.connect(p.GUI)p.setRealTimeSimulation(1)

There are also some example pybullet scripts in Bullet/examples/pybullet. At some stage I'll write some documentation.

Does that work for you?

Statistics: Posted by Erwin Coumans — Sat Oct 15, 2016 6:04 pm

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-15T17:05:27+00:00

Loading a URDF lets you specify collision shapes, mass, inertia, constraints etc.

It is work-in-progress, there is not much documentation for the new API yet, I would suggest try getting pybullet to run and give some feedback.
There are a few scripts in Bullet/examples/pybullet.

There will also be C++ access, using Bullet\examples\RoboticsLearning\b3RobotSimAPI.h. Once this is more complete, it will be rename b3PhysicsSimAPI.h...
You will be able to do your own graphics engine of course, and use the Bullet connect 'DIRECT' method (instead of GUI or SHARED_MEMORY).

Ok, first attempt to get pybullet to be built on Linux Mint 17.3, x64 , GCC 4.8.4, Python 3.5.1....
got a linker error, see below

and CFLAGS / CCFLAGS / CPPFLAGS = '-fPIC' before the premake4_linux64 or make command didnt have an effect

Input:

CPPFLAGS='-fPIC' ./premake4_linux64 --enable_pybullet --python_include_dir="/home/martin/BlenderSVN/build/bin/2.78/python/include/python3.5m"
--python_lib_dir="/home/martin/BlenderSVN/build/bin/2.78/python/lib/python3.5" gmake

and make in the gmake dir

Output...(snip)

...
==== Building BulletFileLoader (release64) ====
==== Building BulletWorldImporter (release64) ====
==== Building pybullet (release64) ====
Linking pybullet
/usr/bin/ld: ../../bin/libBulletExampleBrowserLib_gmake_x64_release.a(OpenGLExampleBrowser.o): relocation R_X86_64_32 against `.rodata.str1.1' can not be used when making a shared object; recompile with -fPIC
../../bin/libBulletExampleBrowserLib_gmake_x64_release.a: error adding symbols: Bad value
collect2: error: ld returned 1 exit status
make[1]: *** [../../bin/libpybullet_gmake_x64_release.so] Error 1
make: *** [pybullet] Error 2

Statistics: Posted by scorpion81 — Sat Oct 15, 2016 5:05 pm

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-15T15:56:08+00:00

Loading a URDF lets you specify collision shapes, mass, inertia, constraints etc.

It is work-in-progress, there is not much documentation for the new API yet, I would suggest try getting pybullet to run and give some feedback.
There are a few scripts in Bullet/examples/pybullet.

There will also be C++ access, using Bullet\examples\RoboticsLearning\b3RobotSimAPI.h. Once this is more complete, it will be rename b3PhysicsSimAPI.h...
You will be able to do your own graphics engine of course, and use the Bullet connect 'DIRECT' method (instead of GUI or SHARED_MEMORY).

Statistics: Posted by Erwin Coumans — Sat Oct 15, 2016 3:56 pm

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-15T15:42:53+00:00

Another question... since the pybullet wrapper seems not exactly what i can use for the purpose of operating bullet via python
Why not?

pybullet and the underlying shared memory C-API will be the new Bullet 3.x API. I plan to create a backend so you can automatically select Bullet 2.x or Bullet 3.x (or other physics engines) under the hood. Those Bullet 3.x bindings will start happenening around PhysicsServerCommandProcessor.cpp...

Ah ok, well i guess i did not understand yet how this new shared memory C-API works. Like... which commands in particular are necessary to replicate the basic HelloWorld example from the (old) wiki ?
Like building a world, adding rigidbodies, setting shapes, adding constraints ?
Is there some documentation i might have overlooked ?

Statistics: Posted by scorpion81 — Sat Oct 15, 2016 3:42 pm

Re: Good / simple introduction example / docs for Bullet 3 G

2016-10-15T15:37:47+00:00

Another question... since the pybullet wrapper seems not exactly what i can use for the purpose of operating bullet via python

Why not?

pybullet and the underlying shared memory C-API will be the new Bullet 3.x API. I plan to create a backend so you can automatically select Bullet 2.x or Bullet 3.x (or other physics engines) under the hood. Those Bullet 3.x bindings will start happenening around PhysicsServerCommandProcessor.cpp...

Statistics: Posted by Erwin Coumans — Sat Oct 15, 2016 3:37 pm