def merge_shapes(shape_a,shape_b,vis=False):
bo=BooleanOp()
print "Shape_a,shape_b: ",shape_a,shape_b
bo.step1_add_lines(shape_a,shape_b)
bo.step2_intersect_lines()
bo.step3_create_edges()
bo.step4_eliminate_deadends()
bo.step5_create_cells()
print "Calling determine hierarchy"
bo.step5b_determine_cell_hierarchy()
#dump_cells(bo)
bo.step6_determine_cell_cover()
bas=BooleanOrStrategy()
bo.step7_classify_cells(bas)
bo.step8_merge_cells();
bo.step9_calc_result();
#bo.step10_eliminate_enclosed_cells();
#bo.step8_merge_cells()
#bo.step9_calc_result()
shape=bo.step11_get_result()
polys=list(shape.get_polys())
if vis:
plines=set()
for poly in polys:
#print "Poly: %s %s"%(poly.get_kind_str(),list(poly.get_lines()))
plines=plines.union(frozenset(poly.get_lines()))
sqs=[]
for line in plines:
sqs.append(visualize.Line(
line.get_v1().get_x(),
line.get_v1().get_y(),
line.get_v2().get_x(),
line.get_v2().get_y(),
(255,0,0)))
draw_things(sqs)
return shape
