forConstruction option in offset2d

[marcus7070]

I often want to use Workplane.offset2D to create construction geometry. For example:

board_dims = (100, 50)
w = (
    cq.Workplane()
    .box(*board_dims, 1)
    .faces(">Z")
    .workplane()
    .rect(*board_dims)
    .offset2D(-2.4)
    .vertices()
    .hole(3)
)

Which actually works just fine:

Until you go to use w.ctx.pendingWires, for example:

board_dims = (100, 50)
w = (
    cq.Workplane()
    .box(*board_dims, 1)
    .faces(">Z")
    .workplane()
    .rect(*board_dims)
    .offset2D(-2.4)
    .vertices()
    .hole(3)
    .faces(">Z")
    .workplane()
    .circle(10)
    .extrude(1)
)

And now you realise offset2D leaves the shape in pendingWires.

Is it worth adding a forConstruction option, similar to rect and other methods?

[adam-urbanczyk]

+1, good idea.

[marcus7070]

I would think a typical use case would be:

w = (
    cq.Workplane
    .rect(10, 10, centered=False, forConstruction=True)
    .offset2D(-1, forConstruction=True)
    .vertices()
    .hole(1)
)

So currently offset2D gets wires from pendingEdges and pendingWires.

cadquery/cadquery/cq.py

Lines 3675 to 3693 in 184a985

	def offset2D(
	self, d: float, kind: Literal["arc", "intersection", "tangent"] = "arc"
	) -> "Workplane":
	"""
	Creates a 2D offset wire.
	:param float d: thickness. Negative thickness denotes offset to inside.
	:param kind: offset kind. Use "arc" for rounded and "intersection" for sharp edges (default: "arc")
	:return: CQ object with resulting wire(s).
	"""
	ws = self._consolidateWires()
	rv = list(chain.from_iterable(w.offset2D(d, kind) for w in ws))
	self.ctx.pendingEdges = []
	self.ctx.pendingWires = rv
	return self.newObject(rv)

To enable it to work off construction geometry, I think when forConstruction=True, offset2D should take wires from self.objects and not do anything with pendingEdges and pendingWires. Does that sound right @adam-urbanczyk? I want to make sure I get this right because I think this is the first method that transforms construction geometry, and I would hate to set a bad precedent.

[jmwright]

@marcus7070 Are you blocked on this? You probably won't find a 1-to-1 comparison with offset2d in the codebase, but you could take a look at how forConstruction is handled currently other places to see if you can find a precedent.

[adam-urbanczyk]

@marcus7070 I'm not sure what the possible issue is. Does something go wrong, if you just set the forConstruction field of the generated wire?

[marcus7070]

Not blocked, thanks.

Out of the two methods (taking edges from self.objects or pending wires/edges when forConstruction=True), I decided that self.objects made more sense to me and wrote the code, tests (marcus7070@5e3fb9e) and an example based off that (marcus7070@e3cdb52).

Then I noticed that Workplane.wire already uses pending edges/wires. So I will rewrite my stuff to keep in line with the existing code.

cadquery/cadquery/cq.py

Lines 2079 to 2117 in d1ebfba

	def wire(self, forConstruction: bool = False) -> "Workplane":
	"""
	Returns a CQ object with all pending edges connected into a wire.
	All edges on the stack that can be combined will be combined into a single wire object,
	and other objects will remain on the stack unmodified
	:param forConstruction: whether the wire should be used to make a solid, or if it is just
	for reference
	:type forConstruction: boolean. true if the object is only for reference
	This method is primarily of use to plugin developers making utilities for 2-d construction.
	This method should be called when a user operation implies that 2-d construction is
	finished, and we are ready to begin working in 3d
	SEE '2-d construction concepts' for a more detailed explanation of how CadQuery handles
	edges, wires, etc
	Any non edges will still remain.
	"""
	edges = self.ctx.pendingEdges
	# do not consolidate if there are no free edges
	if len(edges) == 0:
	return self
	self.ctx.pendingEdges = []
	others = []
	for e in self.objects:
	if type(e) != Edge:
	others.append(e)
	w = Wire.assembleEdges(edges)
	if not forConstruction:
	self._addPendingWire(w)
	return self.newObject(others + [w])

[marcus7070]

I'm not sure what the possible issue is.

I had some misconceptions about pending wires and construction geometry. I was thinking that it should be possible to chain construction geometry calls together, like w = Workplane().rect(1, 1, forConstruction=True).offset2D(1, forConstruction=True). I was also thinking that turning pending wires into construction geometry should not be allowed, since pending wires are:

cadquery/cadquery/cq.py

Lines 85 to 87 in d1ebfba

	self.pendingWires = (
	[]
	) # a list of wires that have been created and need to be extruded

But I've come around now, there is no other way to do the simple Workplane().vLine(1).hLine(1).close().offset2D(1, forConstruction=True) except to use pending edges.

I'll get the PR done today or tomorrow.