You cannot completely disable all CGAL code paths, as certain features (like minkowski) still requires CGAL.

..but this should get you one step closer:

openscad -o test.png  test.scad --backend=manifold

-Marius

The model in question works interactively if I preview it and fails if I
render with CGAL.  It succeeds if I render with manifold.  However, working
around this case, e.g. by enabling manifold, isn't really a solution.  I
need to be able to preview non-manifold models and write out their PNG
image.  I also need it to be as fast as possible.  This is the code base
that generates all the hundreds of example images in the BOSL2 wiki, which
apparently works for Revar using the 2022.08.22 build.  But I don't have
that build.  And apparently the code uses some options that don't exist in
2021.01, so I can't use that version.

Hmmm.  Actually I just realized that it works in CGAL in 2021.01.  It only
fails CGAL in 2025.04.29.  And the failure is odd.  It's an assertion
failure, and then it produces the geometry anyway:

ERROR: CGAL error in CGALUtils::applyUnion3D: CGAL ERROR: assertion
violation!

Expr: itl != it->second.end()

File:
/build/openscad-nightly/stage/usr/include/CGAL/Nef_3/SNC_external_structure.h

Line: 1078

On Sun, Jun 1, 2025 at 7:07 PM Marius Kintel via Discuss <
discuss@lists.openscad.org> wrote:

Why is previewing with manifold not an option? That’s soon going to be the default preview mechanism.

The CGAL regression is worth looking into though.

Do you have a minimal example or two that demonstrates the issues in question?

1. Why --backend=manifold isn’t viable
2. Highlights the CGAL regression

-Marius

This is my current example:

include<BOSL2/std.scad>
cuboid([30,40,50], rounding=8, teardrop=true);

As long as you can still preview---presumably without errors---things which
are not valid manifolds then --backend=manifold is likely OK, though if
it's even a little bit slower that's unfortunate.

On Sun, Jun 1, 2025 at 7:45 PM Marius Kintel marius@kintel.net wrote:

Yeah, --backend=manifold only specifies using the Manifold library instead of CGAL. It doesn’t impose any additional limit on what geometry can be previewed.

In terms of performance, this is a casual test on the examples you posted:

• 2021.01: 5.2 sec
• 2025.05.16 CGAL mode: 16.3 sec
• 2025.05.16 Manifold mode:  1.85 sec

I’ll put the CGAL performance regression on my list, but I feel that the manifold option will be vastly superior :)

-Marius

My results are a little different than what you posted.

2021.01 reports 0.050 seconds
2025.04.29 CGAL reports 9.6 seconds
2025.04.29 Manifold reports 1.2 seconds

Your result for 2021.01 is very odd.  How can it take 5.2 seconds to
preview this simple model?

We have 2973 files to process to produce the BOSL2 docs.  If the processing
time rises by one second per file that adds 50 minutes to the time it takes
to generate the docs which is currently something like 35 minutes.

On Sun, Jun 1, 2025 at 8:48 PM Marius Kintel marius@kintel.net wrote:

Oh, I was running it on a CPU emulator as I don’t an Intel CPU and that build is Intel-only on macOS :/
I’ll re-test and have  deeper look. Thanks for your numbers.

-Marius

On Sun, Jun 01, 2025 at 10:13:33PM -0400, Adrian Mariano via Discuss wrote:

Hi, You state 2021.01 REPORTS ...

I've seen a render take several seconds (like say 5 seconds) and then
OpenScad would report absurdly small numbers like 0.05 seconds.

The version x.y reports are not accurate....

Roger. 

--
** R.E.Wolff@BitWizard.nl ** https://www.BitWizard.nl/ ** +31-15-2049110 **
** Verl. Spiegelmakerstraat 37 2645 LZ  Delfgauw, The Netherlands.
** KVK: 27239233    **
f equals m times a. When your f is steady, and your m is going down
your a** is going up.  -- Chris Hadfield about flying up the space shuttle.
**  'a' for accelleration.

On 6/1/2025 4:06 PM, Marius Kintel via Discuss wrote:

But what's triggering using CGAL?

Generating a PNG should be a preview operation, not a render, and so
(except for a few operations) avoid CGAL entirely.

Offhand, these should trigger CGAL:  render(), rescale(), projection(),
minkowski(), hull().