LWN: Comments on "The programmer's CAD: OpenSCAD"

Why $ in variable names?

michaelkjohnson — Thu, 03 Sep 2020 19:28:17 +0000

TIL!

It surprises me not at all that nophead (of NopSCADlib) provides an example taking advantage of the dynamic scope:

http://forum.openscad.org/Special-variable-scoping-rules-...

Why $ in variable names?

t-paul — Thu, 03 Sep 2020 16:55:46 +0000

There is also a difference in scoping. The "$" variables are dynamically scoped so using them for everything could cause unexpected results.

MCAD and NopSCADlib

coogle — Thu, 27 Aug 2020 18:13:40 +0000

Oh wow, I wasn't familiar with NopSCADlib, that's a great package of components. Thanks for the tip!

Implicit union

coogle — Thu, 27 Aug 2020 18:10:56 +0000

Thank you for pointing that out, I can see how that sentence might accidentally send people down the wrong road -- I was not explicit on using union() use in conjunction with difference() there.

Why $ in variable names?

coogle — Thu, 27 Aug 2020 18:05:37 +0000

There isn't a technical reason why I prefaced variables with $, other than perhaps force of habit from other languages. It is a habit I should break for OpenSCAD code, because you are correct that things like $fa and $fs carry special meaning and I wouldn't want to accidentally create a problem there.

MCAD and NopSCADlib

gerdesj — Thu, 27 Aug 2020 16:07:05 +0000

Thanks for that. The quality of the documentation for NopSCADlib is awesome.

My printer is going to be very busy soon.

SolidPython and ViewSCAD

esemwy — Thu, 27 Aug 2020 12:08:49 +0000

I’m partial to SolidPython and ViewSCAD in a Jupyter notebook. I find it less clunky than the Qt app, and, of course, python.

https://solidpython.readthedocs.io/en/latest/
https://github.com/nickc92/ViewSCAD

Why $ in variable names?

smurf — Thu, 27 Aug 2020 06:37:55 +0000

Some people code like everything is Perl ...?

MCAD and NopSCADlib

michaelkjohnson — Wed, 26 Aug 2020 23:27:23 +0000

It is reasonably common to have MCAD packaged with OpenSCAD; for example, Fedora packages both openscad and openscad-MCAD.

If you are designing anything that uses components similar to those used in 3D printing, you might find NopSCADlib worth looking though. It has an amazing variety of carefully-modeled components.

Why $ in variable names?

michaelkjohnson — Wed, 26 Aug 2020 23:20:18 +0000

In my OpenSCAD experience, $ is used for reserved variables such as $fn, and normal variables are not commonly prefixed with a $. I see that you used both a $ and a $_ convention that I don't recognize from other OpenSCAD exemplars. Is there a reason beyond personal convention for this form in your example?

Implicit union

michaelkjohnson — Wed, 26 Aug 2020 23:15:30 +0000

A minor clarification that might help those just learning OpenSCAD:

At this point in the process, the cylinder and cube are independent, overlapping solids to OpenSCAD. To join them together, we wrap the code with a union operation, which takes all of the solids defined within it and combines them into a single solid in the model.

That's potentially misleading, depending on how it is read. The union operator is not needed to merely fuse geometrical elements. OpenSCAD doesn't have a concept of physically-conjoint independent objects, and mere concatenation of objects is geometrically sufficient. The union operator is useful in the context of other operators that interpret their child objects depending on position, primarily difference, as in the case that you used it. It's used to organize the object tree before rendering, and doesn't add semantics to the rendering process itself. Put another way, you are grouping operations not solids.

From the manual's documentation of union:

Remark: union is implicit when not used. But it is mandatory, for example, in difference to group first child nodes into one.

I've seen plenty of OpenSCAD code that overuses union and in fact especially in my first OpenSCAD code overused it a lot before I understood that point.