from pyx import canvas,path,color
from math import sqrt,tan,asin

pov = (-20,6,5)
x,y,z = 2,1,0
radius = 0.05
scale = 10.0
vertexColor = [color.rgb.red]
edgeColor = [color.rgb.black]

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

def vertex(p):
    lx,ly = perspective(p)
    prad = scale*1.1*tan(asin(radius/(distance(p,pov))))
    c.fill(path.circle(lx,ly,prad),vertexColor)

def edge(p,q):
    lx1,ly1 = perspective(p)
    lx2,ly2 = perspective(q)
    c.stroke(path.line(lx1,ly1,lx2,ly2),edgeColor)

c = canvas.canvas()

for i in range(3):
    for j in range(3):
        edge((i,j,0),(i,j,2))
        edge((i,0,j),(i,2,j))
        edge((0,i,j),(2,i,j))

for i in range(3):
    for j in range(3):
        for k in range(3):
            vertex((i,j,k))

c.writePDFfile("Gray configuration")