[Pyode-user] pyODE in Blender 3D

[Gabriel B. <gb...@ne...>]

Hi everybody,

I'm Gabio from the Blender community. Artist and python coder. Blender 
is an opensource 3D package using python as main scripting language. The 
API is accessible 
here:http://www.blender.org/modules/documentation/237PythonDoc/frames.html .
I recently tried to simulate some tests scenes in Blender using the 
pyODE module. And it worked relatively well. I got a problem though. A 
crash to be more correct, when having a lot of bodies in the same space. 
The fact is I want all of them to be able to collide. I'm not aware ODE 
have limit in the number of collisions it can manage.
To test it out. you can get Blender 3D @ www.blender.org. have python 
2.3 installed and pyODE.
Then download this file: 
http://web.netrevolution.com/gbeloin/ODE_bug_gabio.blend
You can open it in Blender by pressing F1 and browsing to the .blend 
file or double click on it (Windows)
You will then face a screen with the scene (plane and ball) and a script 
windows on the right. to start the test move your mouse cursor in the 
text windows and press ALT-P. for me it crash. in the near_callback. and 
the debug give me a stack overflow. If you go at line 95 and change     
"for x in range(20):" to "for x in range(5):" the script doesn't crash 
anymore. you then can see the anim by moving your mouse in the 3Dspace 
on the left and pressing ALT-A.
or you can see the result of the best i could get out of pyODE before 
crash: http://media.putfile.com/Render_legowall0001_0200
So I'm limited in the number of bodies i can include in the same space?

Of course if you don't feel like downloading Blender and python 2.3, 
I've made an example you can run on any system with pyODE. The crash is 
instant:

--------------------------------------
import ode

def draw_body(body):
    global frame
    x,y,z = body.getPosition()
    print x,y,z

# Collision callback
def near_callback(args, geom1, geom2):
    """Callback function for the collide() method.
    This function checks if the given geoms do collide and
    creates contact joints if they do.
    """
    # Check if the objects do collide
    contacts = ode.collide(geom1, geom2)
    # Create contact joints
    world,contactgroup = args
    for c in contacts:
        c.setBounce(.5)
        c.setMu(7000)
        j = ode.ContactJoint(world, contactgroup, c)
        j.attach(geom1.getBody(), geom2.getBody())

# Create a world object
world = ode.World()
world.setGravity((0,0,-9.81))
world.setERP(0.2) #error correction
world.setCFM(1E-10) #softness of collision

lobj = []
lbody = []
contactgroup = ode.JointGroup()

print "Create a space object"
space = ode.Space()

print "Create a plane geom which prevent the objects from falling forever"
floor = ode.GeomPlane(space, (0,0,1), 0)

print "create array"
a = 1.5
for z in range(20):
    for x in range(20):
        lobj.append((x*3+a,1,z+.5))
for obj in lobj:       
    body = ode.Body(world)
    M = ode.Mass()
    M.setBox(5000,3,1,1)
    body.setMass(M)
    body.setPosition(obj)
    geom = ode.GeomBox(space,(3,1,1))
    geom.setBody(body)
    lbody.append(body)
    body.disable() #wait for the cue
   
bball = ode.Body(world)
M = ode.Mass()
M.setSphere(700,5)
bball.setMass(M)
bball.setPosition((9,-19,5))
geom2 = ode.GeomSphere(space,5)
geom2.setBody(bball)
bball.setLinearVel((0,20,0)) #give some speed.
lobj.append((9,-19,5))
lbody.append(bball)

print "Simulation loop..."

fps = 24
dt = 1.0/fps
frame = 1 #first frame
totframe = 300
while frame < totframe: #tot of frame to do
    for i in range(2):
        space.collide((world,contactgroup), near_callback) #colision
        for b in range(len(lbody)):
            draw_body(lbody[b])
        world.quickStep(dt) #shift time
        contactgroup.empty() #empty mem
    frame += 1
ode.CloseODE()
print "done!"

-------------------------
Thanks for looking.