BRep_Builder constructor

[fnoble]

Hi,

Not sure if this is a bug or my incorrect usage but the following snippet:

from OCC.TopoDS import TopoDS_Compound
from OCC.BRep import BRep_Builder
c = TopoDS_Compound()
bb = BRep_Builder()

was giving the following exception:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-1-215db27b1dce> in <module>()
      4 from OCC.BRep import BRep_Builder
      5 
----> 6 bb = BRep_Builder()
      7 bb.MakeCompound(c)
      8 bb.Add()

/usr/local/lib/python2.7/site-packages/OCC/BRep.py in __init__(self, *args, **kwargs)
    126 class BRep_Builder(OCC.TopoDS.TopoDS_Builder):
    127     thisown = _swig_property(lambda x: x.this.own(), lambda x, v: x.this.own(v), doc='The membership flag')
--> 128     def __init__(self, *args, **kwargs): raise AttributeError("No constructor defined")
    129     __repr__ = _swig_repr
    130     def MakeFace(self, *args):

AttributeError: No constructor defined

I "fixed" it by removing the line:

%nodefaultctor BRep_Builder;

from BRep.i but I'm not sure if this is the correct thing to do.

Thanks,
Fergus

[tpaviot]

You're right it was on my todo list. Actually BRep_Builder default
constructor is not public, it's protected (as far as I remember). But I
have to find a more general rule, because this may be the case for other
classes.

2014-10-08 10:25 GMT+02:00 Fergus Noble notifications@github.com:

Hi,

Not sure if this is a bug or my incorrect usage but the following snippet:

from OCC.TopoDS import TopoDS_Compound
from OCC.BRep import BRep_Builder
c = TopoDS_Compound()
bb = BRep_Builder()

was giving the following exception:

---

AttributeError Traceback (most recent call last)
in ()
4 from OCC.BRep import BRep_Builder
5
----> 6 bb = BRep_Builder()
7 bb.MakeCompound(c)
8 bb.Add()

/usr/local/lib/python2.7/site-packages/OCC/BRep.py in init(self, _args, *_kwargs)
126 class BRep_Builder(OCC.TopoDS.TopoDS_Builder):
127 thisown = _swig_property(lambda x: x.this.own(), lambda x, v: x.this.own(v), doc='The membership flag')
--> 128 def init(self, _args, *_kwargs): raise AttributeError("No constructor defined")
129 repr = _swig_repr
130 def MakeFace(self, *args):

AttributeError: No constructor defined

I "fixed" it by removing the line:

%nodefaultctor BRep_Builder;

from BRep.i but I'm not sure if this is the correct thing to do.

Thanks,
Fergus

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#17.

[fnoble]

I'm now getting a segfault in BRep_Builder::Add :( Do you think this is a result of the default SWIG constructor?

Full code snippet:

    def update_geometry(self):
        c = TopoDS_Compound()
        bb = BRep_Builder()
        bb.MakeCompound(c)
        for child in self.children:
            bb.Add(c, child.geometry)

        self.geometry = c

[jf---]

you probably should utilize a TopoDS_Builder rather than a BRep_Builder instance

def compound(topo):
    '''
    accumulate a bunch of TopoDS_* in list `topo` to a TopoDS_Compound
    @param topo: list of TopoDS_* instances
    '''
    bd = TopoDS_Builder()
    comp = TopoDS_Compound()
    bd.MakeCompound(comp)
    for i in topo:
        bd.Add(comp,i)
    return comp

[tpaviot]

@fnoble It's not possible to conclude without any further clue about the shapes you pass to the builder. The issue is not related to the BRep_Builder constructor.

[fnoble]

Thanks for the tip.

Unsurprisingly TopoDS_Builder (with the SWIG file changed to use a default constructor) also results in a segfault.

The shapes I am passing are simple cylinders right now. Here is a full example showing the segfault:

from OCC.BRepPrimAPI import BRepPrimAPI_MakeCylinder
from OCC.TopoDS import TopoDS_Compound, TopoDS_Builder
from OCC.gp import gp_Trsf, gp_Vec
from OCC.TopLoc import TopLoc_Location

cyl1 = BRepPrimAPI_MakeCylinder(10, 10).Shape()
trsf = gp_Trsf()
trsf.SetTranslation(gp_Vec(0, 0, 0))
cyl1.Move(TopLoc_Location(trsf))

cyl2 = BRepPrimAPI_MakeCylinder(10, 10).Shape()
trsf = gp_Trsf()
trsf.SetTranslation(gp_Vec(30, 0, 0))
cyl2.Move(TopLoc_Location(trsf))

c = TopoDS_Compound()
bb = TopoDS_Builder()
bb.MakeCompound(c)
for child in [cyl1, cyl2]:
    bb.Add(c, child)

[jf---]

that code runs fine in pythonocc 0.6
@tpaviot looks like a welcome addition to the unittests?

[fnoble]

I should probably mention this is with OCE 0.16 (from the homebrew/science tap) with brewed python 2.7.8 and SWIG 3.0.2 on OS X 10.9.4

[tpaviot]

I confirm the bug and the regression.

[fnoble]

Ok, I have a fix. In TopoDS.i change:

250:        void MakeCompound (TopoDS_Compound  C);

to

250:        void MakeCompound (TopoDS_Compound & C);

The problem was that when SWIG was passing by value, C's destructor would get called and blow away the myTShape handle.

It seems like this probably applies to many other place as I see lots of missing &. Are these SWIG interface files generated somehow or are they manually created?

[tpaviot]

@fnobles Yes you're absolutely right, I already pushed a fix yesterday (see https://github.com/tpaviot/pythonocc-core/tree/review/byref-topods-gp).