Dear OpenSCAD users,

I am trying to design a bottle lid with air channels from the center to the outer diameter. It is a piece for a musical instrument. The code is attached. The shape could be simplified as

rotate_extrude() polygon();
for( i=[0:30] ) {
  hull(){
    translate() sphere();
    translate() sphere();
  }
}

I suffer from a three issues:

(1) Warnings while compiling:
WARNING: Normalized tree is growing past 18000000 elements. Aborting normalization.
WARNING: CSG normalization resulted in an empty tree

I found

Edit -> Preferences -> Advanced -> 3D Preview (OpenCSG) -> Turn off rendering at $fixnum elements

but that did not reenable preview for me.

(2) an empty preview
(3) Wireframe not shown:

• OpenSCAD-2021.01 cannot preview, but can render and can display a wireframe
• OpenSCAD-2024.10.09.ai20850-x86_64.AppImag-manifold-backend can preview, can render, does not display a wireframe
• OpenSCAD-2024.10.09.ai20850-x86_64.AppImag-cgal-backend cannot preview, can render, can display wireframe

What settings may I want to adjust?
May there be a regression in the manifold backend regarding the wireframe display?

Cheers,
Marcus

I think the essence is that preview really hates intersection, and
you're doing a fair number of them.  I think the complexity of one of
the internal data structures is in some way an exponential function of
the number of intersections.

Here's a table of segmente_anzahl versus size of the normalized tree:
1
12
2
32
3
80
4
192
5
448
6
1024
10
24576

However... you're doing something like

for (...) {
intersection() {
rotate(...) luftrohr();
... a cylinder ...
}
}

which is equivalent to

intersection() {
... a cylinder ...
for (...) {
rotate(...) luftrohr();
}
}

only the first does about thirty intersections, while the second only
does one.

I applied Hans solution (making use of the cache by a render()-directive) und would like to highlight my second issue:

cgal-backend can display a wireframe.
manifold-backend cannot.

As manifold is officially stable, I would consider that a regression bug.

Code is attached. Test with:

./OpenSCAD-2024.10.09.ai20850-x86_64.AppImage --backend=manifold 0.23.2_360labium.scad
./OpenSCAD-2024.10.09.ai20850-x86_64.AppImage --backend=cgal 0.23.2_360labium.scad

Cheers,
Marcus