#!/usr/bin/python
#
# slicer.py - FreeCAD-based STL to Gnuplot slicer
#
# Written 2015 by Werner Almesberger
# Copyright 2015 by Werner Almesberger
#
# This program//library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#


import sys

sys.path.append("/usr/lib/freecad/lib")


import FreeCAD, Part, Mesh
import os, getopt
from FreeCAD import Base
from math import hypot


epsilon = 0.0001	# acceptable math rounding error and slicing offset
mech_eps = 0.01		# acceptable mechanical deviation
margin = None		# draw a workpiece at the specified xy distance around
			# the model (default: none)


def dist(a, b):
	pa = a.Point
	pb = b.Point
	return hypot(pa[0] - pb[0], pa[1] - pb[1])


def print_vec(v):
	p = v.Point
	print p[0], " ", p[1], " ", p[2] - epsilon


def usage():
	print >>sys.stderr, "usage:", sys.argv[0], "file.stl"
	sys.exit(1)


#
# FreeCAD prints progress information to stdout instead of stderr.
# We don't want that ...
#

stdout = os.dup(1)
os.dup2(2, 1)
sys.stdout = os.fdopen(stdout, "w")

opts, args = getopt.getopt(sys.argv[1:], "b:")
for opt, arg in opts:
	if opt == "-b":
		margin = float(arg)
	else:
		assert False

if len(args) != 1:
	usage()

#
# Read the STL mesh
#

mesh = Mesh.Mesh(args[0])

#
# The 2.5D model consists of "plateaus" (facets parallel to the xy plane) and
# "walls" (facets parallel to the z axis). Anything else is an error and will
# produce incorrect results.
#
# We use plateau facets only for their z position, as indication where to mill
# a plateau. Wall facets are kept for later use.
#

vert = Mesh.Mesh()
z_raw = {}
max_nz = 0
inclined = 0
for facet in mesh.Facets:
	if abs(facet.Normal.z) >= 1 - epsilon:
		z_raw[facet.Points[0][2]] = 1
	else:
		nz = abs(facet.Normal.z)
		if nz > epsilon:
			inclined += 1
			max_nz = max(max_nz, nz)
		v1 = Base.Vector(facet.Points[0])
		v2 = Base.Vector(facet.Points[1])
		v3 = Base.Vector(facet.Points[1])
		vert.addFacet(v1, v2, v3)

if inclined:
	print >>sys.stderr	# FreeCAD progress reporting messes up newlines
	print >>sys.stderr, inclined, "inclined facets, maximum normal", max_nz

#
# @@@ This is perhaps a bit too paranoid
#
# I wrote the Z noise filtering because I had mis-read perfectly good
# distinct coordinates as being essentially the same value but with
# rounding errors.
#

z_levels = []
last = None
for z in sorted(z_raw.keys(), reverse = True):
	if last is None or last - z > epsilon:
		z_levels.append(z)
		last = z

#
# Convert the walls to a FreeCAD shape
#

shape = Part.Shape()
shape.makeShapeFromMesh(mesh.Topology, mech_eps)
bb = shape.BoundBox

#
# Iterate over all plateaus and determine how they intersect with the walls.
# For this, we add a small offset to the z position so that we intersect above
# the plateau.
#

for z in z_levels:
	print "# level z = ", z

	if margin is not None:
		print bb.XMin - margin, " ", bb.YMin - margin, " ", z
		print bb.XMax + margin, " ", bb.YMin - margin, " ", z
		print bb.XMax + margin, " ", bb.YMax + margin, " ", z
		print bb.XMin - margin, " ", bb.YMax + margin, " ", z
		print bb.XMin - margin, " ", bb.YMin - margin, " ", z
		print

	for wire in shape.slice(Base.Vector(0, 0, 1), z + epsilon):
		print "# wire = ", wire
		first = None
		last = None
		for e in wire.Edges:
			v = e.Vertexes[0]
			if first is None:
				first = v
			if last is None or dist(v, last) >= mech_eps:
				print_vec(v)
			last = v
		if first is not None:
			print_vec(first)
			print
	print

#
# That's all, folks !
#