I've been working on BOSL2 for a while with Revar, and we have 60k lines of
OpenSCAD code.  Based on that experience, I think that the problem with the
OpenSCAD language is NOT fundamentally that it is functional.  The benefit
of python is NOT fundamentally that it is procedural.  There are two basic
problems with OpenSCAD for doing more complicated user space processing.
One is the inability to gain access to geometry, so to do user space
design, everything from the ground up has to be done "outside" of the
OpenSCAD geometry engine.  The second problem is about efficiency.
OpenSCAD has no data structures.  Graphics algorithms assume access to
sophisticated and efficient data structures like a priority queue or a tree
or other kinds of things that are impossible to implement efficiently in
OpenSCAD.  So, yeah, you can implement the data structure, but instead of
being O(log N) or whatever it will be O(N^2).  So then trying to implement
that process that uses that data structure in user space becomes
intractable.  It's not clear to me that this limitation is fundamentally
about the language being functional.

Note that the filleting process displayed by Sanjeev is straight forward to
implement in principle.  You just find the intersection of two things and
put a fillet there.  Two complications arise for doing this in userspace in
OpenSCAD.  The first is representing the things, because again, you can't
use the geometry engine to do it.  Now maybe a solution to that problem is
coming?  The second complication is dealing with self-intersections of the
resulting polyhedron, because that's intractable in OpenSCAD.  Really it
seems like OpenSCAD should have a primitive that accepts a series of
profiles and links them together into a polyhedron, even if it's
self-intersecting.

Here's examples of doing the fillet problem entirely in OpenSCAD
userspace.  There are many examples at the link below.  I show a single one
in this message.

https://github.com/BelfrySCAD/BOSL2/wiki/rounding.scad#functionmodule-join_prism

[image: image.png]

On Sun, Jul 23, 2023 at 1:14 PM Sanjeev Prabhakar sprabhakar2006@gmail.com
wrote:

I am not sure 3D fillets are any use in FDM printing because of the layers.
I only use 2D fillets to get rounded tool paths.

On Sun, 23 Jul 2023, 20:08 Adrian Mariano, avm4@cornell.edu wrote:

Are you thinking that the layers break the propagation of stress through
the model, causing stress to concentrate at each layer, instead of
concentrating at a corner?  Have you observed that models which fail by
layers shearing do so and random places in the model?

On Sun, Jul 23, 2023 at 3:18 PM nop head nop.head@gmail.com wrote:

Adriano, thank you for your input
I appreciate your work with Revar on BOSL2 and I understand your reasoning
that BOSL2 could become obsolete,
but I am sure it will not. When openscad becomes more powerful, BOSL code
might be able to code with fewer lines, but  BOSL2 is still very important
to openscad.

Yes, I would appreciate OpenSCAD to have access to the internal vertices to
read them and work with the coordinates.

Unfortunately this is not as easy, because often a model is developed in
OpenCSG and there are no coordinates available in OpenSCG.
If you accept the fact that a full render has to be performed to get
coordinates of a submodule. It's just a matter of a PR.
If somebody guarantees,  that such a PR will actually be accepted/merged,
time to develop on such a PR would not be an issue.

My Main Problem with SCAD language is that variables cannot be reassigned,
once they are set -> could probably be solved with most other interpreter
languages.
The main benefit I see with python is not the opposite of the previous
statement.  Python is just any interpreter language choice. but its very
easy to learn and very easy to read.
PLUS: it has many accompanying libraries which will help you to do fancy
stuff with OpenSCAD.
for example this one:

http://guenther-sohler.net/openscad/examples/qrcode.txt
these few lines of code creates an qr code display object , which you can
scan  with your mobile. (Yes, i have seen openscad qr code libs, but this
one appears easier and has more options)

And your second statement : OpenSCAD has datastructures is also valid.
Polyhedra are composed of triangles which are stored as coordinates only!
It would be much better to compose triangles from
indices into a global vertex array. This is something I am right now
working on.(some ctests are not passed for my PR)
Information which could also be stored with the  "indexed " polygons is: a
lookup table from point -> which triangles use this point.

And Yes, I like your fillet and I personally appreciate , if Sanjeev's
knowledge could go into GeomtryEvaluator.cc

In the End, I'd like to see openscad become more powerful by being able to
change variables once they are set and to use external libs.
And yes, I know that I am aware that people might see this as a security
risk, but those people can stay safe and do not even need to bother when
not activating it.
The rest and the interested people instead can leverage the new power
coming from python.

Thank you for reading

On Sun, Jul 23, 2023 at 9:08 PM Adrian Mariano avm4@cornell.edu wrote:

The fact that prints always break along layer lines means adding a fillet
that is made of layers hardly affects the strength in my opinion.

On Sun, 23 Jul 2023, 20:24 Adrian Mariano, avm4@cornell.edu wrote:

nop head, this might be true with  an original print.
But if you e.g. handle ABS with acetone this is no longer the case.
In that case objects with  fillets will break far less than an inbound
sharp corner

cylinder(d=20,h=2);
cylinder(d=5,h=20);

the "edge" between the cylinder might very easily break, but you improve
the strength dramatically when you add a fillet instead.

On Sun, Jul 23, 2023 at 10:00 PM nop head nop.head@gmail.com wrote:

I'm confused...

On 2023-07-23 12:45 p.m., Guenther Sohler wrote:

I must have misunderstood your statement as it seems to me to say that
you're working on something that OpenSCAD's polyhedron command already
does: it takes a single list of vertices and each face is defined by a
list of vertex indices.

Could you clarify for me, please.

Steve

Sorry Steve,

I actually did not express myself very well.

you you create  cube in openscad, its stored internal as
6 faces, each containing 4 vertices and each vertices contains 3 values
representing x/y/z

the internal representation of openscad is actually triangles containing
coordinates instead of indices.

if you use openscad  polyhedron command in openscad of course you specity a
point list and a faces list containing indices.
but its immediately translated to this stupid coordinate-only format.

it would be much better if openscad object would interally contain:

• a list of vertices
• a list of polygons whereas each polygon is just a list of indices.

This is what i am currently working on and Marius appears to appreciate it,
but he wants a "Polygon Builder" in addition.

On Sun, Jul 23, 2023 at 10:15 PM Steve Lelievre <
steve.lelievre.canada@gmail.com> wrote:

Ah, now I understand.

Thanks

On Sun, Jul 23, 2023 at 13:23, Guenther Sohler guenther.sohler@gmail.com
wrote:

--
Cell +1 778 837 5771

On Sun, Jul 23, 2023 at 09:00:06PM +0100, nop head wrote:

In some cases, you can print it so that the largest load ends up in
the X or Y direction and then a fillet perpendicular to that ends up
being printed in one layer in the XY plane. This can benefit from the
fillet from strength.

That said: I think also a fillet in the other direction will help with
strength. I have seen objects delaminate exactly in the stresspoint
where a fillet would have helped.

And even if it doesn't help, it looks nice and less "openscad-like".

Roger. 

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