Creating a hierarchy and using expressions

This script creates a hierarchy of objects so that moving the parent will automatically move the children as well. The animation is created by using expressions.

Here is the script:

######################################################################
# Creating a hierarchy and using expressions
######################################################################

# Camera
TargetCamera(
    pos    = vec3(2,1,2.5),
    target = vec3(0,0,0),
    fov    = 40
)

# Lights
GLTargetDistantLight( pos=(0,0,1) )
GLTargetDistantLight( pos=(0,0,-1), diffuse=(1,0.5,0.2), intensity=2 )

######################################################################
# Center sphere
######################################################################

hub = Sphere(
    radius = 0.3,
    pivot = (0, 0, -0.1),
    material = GLMaterial( diffuse = (0.8,0.85,0.9) )
)

# Animate the center sphere (all other objects will move with it)
e = Expression("mat3().fromEulerZYX(pi*sin(0.2*t), 0, -1.4*t)")
e.output_slot.connect(hub.rot_slot)

######################################################################
# Spokes
######################################################################

# Define the materials for the cylinders and boxes...
mat1 = GLMaterial( diffuse = (1,1,1) )
mat2 = GLMaterial( diffuse = (0.7, 0.3, 0.2) )
mats = [mat1,mat2]

# Create boxes as children of the sphere alternately using mat1 and mat2
numspokes = 20
for i in range(numspokes):
    a = float(i)/numspokes

    # Create cylinders as children of the center sphere
    c = CCylinder(name = "Spoke%d"%i,
        pos = (0,0,0),
        pivot = (0,0,0.5),
        length = 1.0,
        radius = 0.02,
        material = mats[i%2],
        parent = hub
    )

    # Animate the rotation of the cylinder
    # (the z angle will "position" the cylinder at the correct angle around the hub)
    e = Expression("mat3().fromEulerZYX(0, 0.3*sin(%f+2*t)+pi/2, %f)"%(4*a*pi, 2*a*pi))
    e.output_slot.connect(c.rot_slot)

    # Create boxes as children of the cylinder
    b = Box(name = "Box%d"%i,
        pos = (0,0,-0.5),
        lx=0.1, ly=0.3, lz=0.1,
        material = mats[i%2],
        parent = c
    )