Thanks for the input.
I had a chat with eivindkvedalen, and got the suggestion to try splitting my complex part into smaller parts with boolean operations first, and doing the cross sections later. I've tried, and the time reduction was dramatic, the script completes in less than 3 minutes, while running a basic Part -> Cross-sections took 2-3 hours! Goes to show that there's room for some optimisation in FreeCAD.
With this speed increase, I'm not going to pursue the multithreading for now.
Here's my current code, which I simply run by pasting it into the python console in FreeCAD, and then call it as in the example given below.
Code: Select all
from FreeCAD import Base
import Draft
import Part
App=FreeCAD
def bisectCrossSections(obj, layerThickness, layerLocation=0.5):
'''bisectSliceWire(obj, layerThickness, layerLocation) splits an object
into wires at layerThickness intervals along the Z axis, and distributes
the wire shapes on a plane. If you want to laser cut a 3-dimensional
object in 4mm plywood, run bisectSliceWire(object, 4), and you will get
the laser cutting paths necessary.
layerLocation is a range from [0.0, 1.0] that specifies where in each
layerThickness segment the wire should cut, where 0.0 is the bottom,
0.5 is the center, and 1.0 is the top. Values outside the accepted range
are truncated.
This script was initially based on slicePart() from the script available on
http://freecadbuch.de/doku.php?id=blog:schnittmodell_eines_hauses_fuer_den_laser-schneider
This script uses an optimisation for complex objects that includes
cutting the original object into two, and then cutting each segment in
two, repeating until the segments are suitably small. This has resulted
in a time optimisation on the order of 50-60x on my laptop, for a freecad
object that was created from a mesh, as shown in
https://www.youtube.com/watch?v=avVNfIswkMU
'''
layerLocation=max(0.0, layerLocation) # enforce sensible limits
layerLocation=min(1.0, layerLocation)
sections = []
workSections = [obj]
i = 0
while len(workSections) > 0:
o = workSections.pop(0)
b = o.Shape.BoundBox
lx = b.XLength
ly = b.YLength
lz = b.ZLength
if lz < layerThickness:
sections.append(o)
continue
label_boxbothalf = "box_bottom_half_{0}".format(i)
label_bothalf = "bottom_half_{0}".format(i)
label_tophalf = "top_half_{0}".format(i)
# create bottom half with Intersection boolean op
s=App.ActiveDocument.addObject("Part::Box",label_boxbothalf)
s.Placement = App.Placement(App.Vector(b.XMin - 1,b.YMin - 1,b.ZMin - 1),App.Rotation(App.Vector(0,0,1),0))
s.Length = lx + 2
s.Width = ly + 2
s.Height = (lz/2) + 1
bottom_half = App.activeDocument().addObject("Part::MultiCommon",label_bothalf)
bottom_half.Shapes = [o, s]
# create top half with Difference boolean op
top_half = App.activeDocument().addObject("Part::Cut",label_tophalf)
top_half.Base = o
top_half.Tool = s
App.ActiveDocument.recompute()
if bottom_half.Shape.BoundBox.ZLength > layerThickness*2:
workSections.append(bottom_half)
else:
sections.append(bottom_half)
if top_half.Shape.BoundBox.ZLength > layerThickness*2:
workSections.append(top_half)
else:
sections.append(top_half)
i = i + 1
g2=App.ActiveDocument.addObject("App::DocumentObjectGroup",str(obj.Label) + "_Slices")
total_zmin = obj.Shape.BoundBox.ZMin
total_zmax = obj.Shape.BoundBox.ZMax
lx = obj.Shape.BoundBox.XLength + 5
ly = obj.Shape.BoundBox.YLength + 5
out_x=0
out_y=0
start_z = total_zmin + (layerThickness * layerLocation)
step = layerThickness
total_step = step
current_z = start_z + total_step
while current_z <= total_zmax:
# Find the correct section in sections[]
for section in sections:
if section.Shape.BoundBox.ZMin <= current_z and section.Shape.BoundBox.ZMax >= current_z:
try:
wires = list()
for i in section.Shape.slice(FreeCAD.Base.Vector(0,0,1),current_z):
wires.append(i)
comp = Part.Compound(wires)
layer = FreeCAD.ActiveDocument.addObject("Part::Feature", "MyLayer")
layer.Shape = comp
layer.purgeTouched()
layer.Placement.Base = FreeCAD.Vector(out_x, out_y, -current_z)
out_x = out_x + lx
if out_x > 400:
out_x = 0
out_y = out_y + ly
g2.addObject(layer)
except Exception as e:
print "Caught exception:", repr(e)
total_step += step
current_z = start_z + total_step
for section in sections:
section.ViewObject.Visibility = False
App.activeDocument().recompute()
My intention was to use this for lasercutting, so a sample run to split an object called "Solid" in FreeCAD into a cross-section every 4mm (to lasercut a part from 4mm plywood for example) would look like this:
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bisectCrossSections(App.ActiveDocument.Solid, 4)
