File:Body centered cubic 35 balls.svg

from PADS import SVG
from math import sqrt,tan,asin
import sys

layers = 2
n = layers**3 + (layers + 1)**3

def ccube(x,y,z):
    return (x & 1) == (y & 1)
dims = range(-layers,layers+1)
rdims = range(layers,-layers-1,-1)
points = [(x,y,z) for x in rdims for y in dims for z in dims
          if x&1 == y&1 == z&1]

pov = (-20,-3.7,6.5)
x,y,z = 2,1,0
radius = 0.65
scale = 1000.0

def distance(p,q):
    return sqrt(sum([(p[i]-q[i])**2 for i in (x,y,z)]))
 
def perspective(loc):
    dz = loc[z]-pov[z]
    return (loc[x]-pov[x])*scale/dz, (loc[y]-pov[y])*scale/dz

bbox = 360+320j
output = SVG.SVG(bbox,sys.stdout)

output.element("defs",1)
output.element('radialGradient id = "light" cx = "50%" cy = "50%" fx = "70%" fy = "15%" r = "55%"',1)
output.element('stop stop-color = "rgb(255,255,255)" offset = "0%"')
output.element('stop stop-color = "rgb(200,200,240)" offset = "15%"')
output.element('stop stop-color = "rgb(0,0,180)" offset = "100%"')
output.element("radialGradient",-1)
output.element("defs",-1)

def vertex(p):
    lx,ly = perspective(p)
    lx += 520
    ly -= 40
    prad = scale*1.1*tan(asin(radius/(distance(p,pov))))
    output.circle(lx+ly*1j,prad,fill=SVG.colors.blue)
    output.circle(lx+ly*1j,prad,fill="url(#light)")

for p in points:
    vertex(p)

output.close()