CadQuery intersection workaround

intersection_example.py

import cadquery as cq
from Helpers import show

# remake of the wikiedia example of a CSG intersect:
#    https://en.wikipedia.org/wiki/Constructive_solid_geometry#Workings

sphere = cq.Workplane("XY").sphere(7.5).translate((5, 5, 5))
box = cq.Workplane("XY").box(10, 10, 10)

def copy(obj):
    return obj.translate((0, 0, 0))

#intersection = sphere.intersect(box)  # doesn't work

def intersect(wp1, wp2):
    """
    Return geometric intersection between 2 cadquery.Workplane instances by
    exploiting.
    A n B = (A u B) - ((A - B) u (B - A))
    """
    neg1 = copy(wp1).cut(wp2)
    neg2 = copy(wp2).cut(wp1)
    negative = neg1.union(neg2)
    return copy(wp1).union(wp2).cut(negative)

intersection = intersect(box, sphere)

# Display the primatives being intersected as shades of red/green
show(sphere, (255, 100, 100, 0.8))  # red
show(box, (100, 255, 100, 0.8))  # green
# Display resulting intersection solid
show(intersection)

result.png

issue: dcowden/cadquery#188
pull-request: dcowden/cadquery#189