export to vertices/indices array?

[fferri]

I am new to cadquery.
Instead of export to file, I would like to export to a pair of arrays for vertices and indices respectively.
I found no such example in the examples dir nor in the manual.
I found the exportStl() code at cadquery/occ_impl/shapes.py:414 however it is not trivial to extract.
I end up with all of this code in my script:

shape = ...

#cq.exporters.export(shape, "shape.stl")

import OCP.TopAbs as ta
from OCP.TopoDS import TopoDS, TopoDS_Shape
from OCP.TopAbs import TopAbs_ShapeEnum, TopAbs_Orientation

downcast_LUT = {
    ta.TopAbs_VERTEX: TopoDS.Vertex_s,
    ta.TopAbs_EDGE: TopoDS.Edge_s,
    ta.TopAbs_WIRE: TopoDS.Wire_s,
    ta.TopAbs_FACE: TopoDS.Face_s,
    ta.TopAbs_SHELL: TopoDS.Shell_s,
    ta.TopAbs_SOLID: TopoDS.Solid_s,
    ta.TopAbs_COMPSOLID: TopoDS.CompSolid_s,
    ta.TopAbs_COMPOUND: TopoDS.Compound_s,
}

def shapetype(obj: TopoDS_Shape) -> TopAbs_ShapeEnum:
    if obj.isNull():
        raise ValueError("Null TopoDS_Shape object")
    return obj.ShapeType()

def downcast(obj: TopoDS_Shape) -> TopoDS_Shape:
    return downcast_LUT[shapetype(obj)](obj)

fileName = 'shape.stl'
tolerance = 1e-3
angularTolerance = 0.1
relative = True
parallel = True

if isinstance(shape, cq.Workplane):
    from cadquery.occ_impl.exporters.utils import toCompound
    shape = toCompound(shape)

wrapped = downcast(shape)

from OCP.BRepMesh import BRepMesh_IncrementalMesh
from OCP.StlAPI import StlAPI_Writer

BRepMesh_IncrementalMesh(
    wrapped, tolerance, relative, angularTolerance, parallel
)

#writer = StlAPI_Writer()
#writer.ASCIIMode = False
#print(writer.Write(wrapped, fileName))

# don't write STL but get the vertices/indices directly

which doesn't even work:

Traceback (most recent call last):
  in <module>
    wrapped = downcast(shape)
              ^^^^^^^^^^^^^^^
  in downcast
    return downcast_LUT[shapetype(obj)](obj)
           ~~~~~~~~~~~~^^^^^^^^^^^^^^^^
KeyError: 'Compound'

so I must have been missed something while extracting the relevant parts.

Is there any simpler approach to this?

[michaelgale]

I presume you mean arrays of triangular mesh vertices and corresponding face indices. In which case you are on the right track with the BRepMesh_IncrementalMesh function from the OCP kernel; however, the steps to get the triangles and vertices is not trivial.
Luckily, my cq-kit repository has this function already implemented with a function triangle_mesh_solid.
Hopefully that helps.

[fferri]

Thanks for your tip. Yes, exporting an in-memory buffer for a triangular mesh is what I am after.

I tried your code with a simple example from the manual I'm working on:

    result = (
        cq.Workplane("XY")
        .box(height, width, thickness)
        .faces(">Z")
        .workplane()
        .hole(diameter)
        .faces(">Z")
        .workplane()
        .rect(height - padding, width - padding, forConstruction=True)
        .vertices()
        .cboreHole(0.024, 0.044, 0.021)
        .edges("|Z")
        .fillet(0.02)
    )
    
    triangles, vertices = triangle_mesh_solid(result)

but it gives me this error:

  File "/opt/homebrew/Caskroom/mambaforge/base/envs/cq/lib/python3.11/site-packages/cqkit/cq_discrete.py", line 121, in triangle_mesh_solid
    mesh = BRepMesh_IncrementalMesh(o, lin_tol, False, ang_tol)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: __init__(): incompatible constructor arguments. The following argument types are supported:
    1. OCP.BRepMesh.BRepMesh_IncrementalMesh()
    2. OCP.BRepMesh.BRepMesh_IncrementalMesh(theShape: OCP.TopoDS.TopoDS_Shape, theLinDeflection: float, isRelative: bool = False, theAngDeflection: float = 0.5, isInParallel: bool = False)
    3. OCP.BRepMesh.BRepMesh_IncrementalMesh(theShape: OCP.TopoDS.TopoDS_Shape, theParameters: IMeshTools_Parameters, theRange: OCP.Message.Message_ProgressRange = <OCP.Message.Message_ProgressRange object at 0x116d72030>)

Invoked with: <cadquery.occ_impl.shapes.Compound object at 0x12360ef50>, 0.01, False, 0.5

which is similar to an error I encountered with my code above...
Forgive me if I'm doing something stupid, as I told you I'm new to CadQuery.

[fferri]

Works if I do:

result = result.val().wrapped

before passing result to triangle_mesh_solid(...).

I would have expected such conversion to be done automatically, i.e. whatever can be exported by CadQuery to a mesh file, should also work by this function...

[michaelgale]

Glad it works