Animation of building double-helix structure with Blender and Python

by Daniel Hnyk

This code was created as my final project number 2 on Computer Graphics in 2015 at FJFI CVUT in Prague. It describes creating double helix like structure, adding lights and cameras and creating simple animation.

import bpy  
from mathutils import *  
from math import pi, sin, cos  
scene = bpy.context.scene

# if exists, delete cube
try:  
    scene.objects.unlink(scene.objects['Cube'])
except:  
    pass


SC = 0.5 # scaling of objects  
ROT = pi/18 # how much at each step bone (dumbbell like part) should be rotated against previous  
RAD = 0.3 # dunno  
LEN = 2.7 # the length of the middle bar  
STEP = 0  
N = 30 # how much of bones should be built

def anim_ob(ob):  
    """This cares about animation of object. 
    It tells when it should hide and reveal."""

    scene.objects.active = ob
    scene.frame_current =  STEP
    bpy.context.active_object.hide_render = True
    bpy.context.active_object.keyframe_insert(  data_path="hide_render", 
                                                index=-1, 
                                                frame=STEP)
    current_frame = STEP + 1
    scene.frame_current =current_frame
    bpy.context.active_object.hide_render = False
    bpy.context.active_object.keyframe_insert(  data_path="hide_render", 
                                                index=-1, 
                                                frame=current_frame)

def create_one_on(x0, y0, z0, rot):  
    """Creates one bone."""

    # create, rotate, add color the middle bar
    bpy.ops.mesh.primitive_cylinder_add(location=(x0,y0,z0))
    cyl = bpy.context.object
    cyl.dimensions = (RAD, RAD, LEN)
    otoc = ROT + rot
    cyl.rotation_euler = (pi/2, 0, otoc)
    matc = bpy.data.materials.new("matc")
    matc.diffuse_color = (0,1,0)
    cyl.data.materials.append(matc)
    anim_ob(scene.objects.active)


    # find out when it starts and ends, so we know where to place cubes                                            
    cyl_end = (-sin(otoc) * cyl.dimensions[2]/2,  (cyl.dimensions[2]/2)*cos(otoc), z0)
    cyl_start = (sin(otoc) * cyl.dimensions[2]/2,  -(cyl.dimensions[2]/2)*cos(otoc), z0)

    # add cubs on given location, rotate and color them
    itr = zip((cyl_start, cyl_end),
                ((1,0,0), (0,0,1)))
    for loc, col in itr:
        bpy.ops.mesh.primitive_cube_add(location = loc, radius=SC)
        mat = bpy.data.materials.new("matl" + str(col[0]))

        mat.diffuse_color = col
        cubl = bpy.context.object
        cubl.data.materials.append(mat)

        cubl.rotation_euler = (0, 0, ROT + rot)

        # this will make the structure animated
        anim_ob(scene.objects.active)

rotac = 0  
cislo_snimku = 0 # number of frame  
for i in range(N):  
    scene.frame_set(cislo_snimku) 
    create_one_on(0, 0, i, rotac) # actually create the object

    STEP += 1
    rotac += ROT

# set 4 suns
zlamp = N//2  
far = 50  
for lm in [(-1*far,1*far,zlamp), (1*far,1*far,zlamp),  
         (1*far,-1*far,zlamp), (-1*far,-1*far, zlamp)]:
    lamp_data = bpy.data.lamps.new(name="lampa", type='SUN')
    lamp_object = bpy.data.objects.new(name="Lampicka", object_data=lamp_data) 
    scene.objects.link(lamp_object)
    lamp_object.location = lm

# set camera on the right spot    
cam = bpy.context.scene.objects['Camera']  
cam.location = (7, 0, N//2)  
cam.rotation_euler = (pi/2, 0, pi/2)  
caml = bpy.data.cameras['Camera']  
caml.lens = 3

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