Hi All,

I’m running some benchmark tests to predict the amount of time I need for the final design and ran into some performance problems.

I calculate the intersection of a cuboid and a circular stack of 680 spheres. I included the script. Please don’t comment the messy setup or the purpose of the script. This is for benchmarking purposes only 😉. See below for the union and intersect within the GUI, as well as a view of the rendered STL in MeshLab.

While the GUI (F5) masters the intersection in less than 1 second, rendering it for STL export (F6) takes 44 minutes (on a Core i9 9900 3.1Ghz with 32GB RAM on an Asus ROG STRIX 8360F motherboard). Also, the memory consumption of OpenSCAD grows from 250 MB to more than 8 GB at the end of the rendering process.

Below is a screenshot of Sysinternals, showing that OpenSCAD uses up to 8 GB memory and 6.4% CPU for this script (the latter indicating that the script runs single threaded).

Why does the rendering process take so long and why does it take so much memory?

Pete.

Hi Ron,

Thanks for the advice.

$fn is related to the number of facets, so I cannot imagine that -5 is a legal value (although OpenSCAD seems to accept $fn=-5 without warning. Waiting on the results though…).

Setting $fn=25 is the minimum, otherwise the volume calculations of the spheres become too inaccurate. With a $fn=5 for example, your sphere volume calculations are almost a factor of 2 away from the analytical result.

$fn scales relatively linear to the calculation duration, by the way which sounds quite logical.

Regards,

Pete.

From: Discuss discuss-bounces@lists.openscad.org On Behalf Of Ron Wheeler via Discuss
Sent: Thursday, August 13, 2020 13:00
To: discuss@lists.openscad.org
Cc: Ron Wheeler rwheeler@artifact-software.com
Subject: Re: [OpenSCAD] Slow rendering performance and high memory consumption when exporting a 3D STL

http://forum.openscad.org/basic-questions-fn-td22360.html
Might help.

I am not sure what you are benchmarking against and what the equivalent $fn and $fs values that you are using in the comparison software.

Try setting your $fn to a very low value - 5??? and see what affect that has.

Ron

On 2020-08-13 6:43 a.m., peter_osc@xs4all.nl mailto:peter_osc@xs4all.nl  wrote:

Hi All,

I’m running some benchmark tests to predict the amount of time I need for the final design and ran into some performance problems.

I calculate the intersection of a cuboid and a circular stack of 680 spheres. I included the script. Please don’t comment the messy setup or the purpose of the script. This is for benchmarking purposes only 😉. See below for the union and intersect within the GUI, as well as a view of the rendered STL in MeshLab.

While the GUI (F5) masters the intersection in less than 1 second, rendering it for STL export (F6) takes 44 minutes (on a Core i9 9900 3.1Ghz with 32GB RAM on an Asus ROG STRIX 8360F motherboard). Also, the memory consumption of OpenSCAD grows from 250 MB to more than 8 GB at the end of the rendering process.

Below is a screenshot of Sysinternals, showing that OpenSCAD uses up to 8 GB memory and 6.4% CPU for this script (the latter indicating that the script runs single threaded).

Why does the rendering process take so long and why does it take so much memory?

Pete.

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Hi Ron,

Results are here.

With $fn=-5, calculation duration decreases from 44 to 22 minutes. I don’t know why.

I cannot find any documentation about negative $fn values though, except that its minimum value is 0.01.

By the way, I am benchmarking OpenSCAD/CGAL against FreeCAD/Opencascade here.

FreeCAD/OpenCascade does this job in less than a second and I don’t see fundamental differences in the STL files that are produced, except some minor differences in the placement of facets, and the fact that FreeCAD produces a binary STL instead of ASCII.

So there is still a difference in performance of a factor of 1000 in this case which is worth considering for me.

Below a screenshot of both designs in OpenSCAD and FreeCAD.

Pete.

From: Discuss discuss-bounces@lists.openscad.org On Behalf Of peter_osc@xs4all.nl
Sent: Thursday, August 13, 2020 13:32
To: 'OpenSCAD general discussion' discuss@lists.openscad.org
Subject: Re: [OpenSCAD] Slow rendering performance and high memory consumption when exporting a 3D STL

Hi Ron,

Thanks for the advice.

$fn is related to the number of facets, so I cannot imagine that -5 is a legal value (although OpenSCAD seems to accept $fn=-5 without warning. Waiting on the results though…).

Setting $fn=25 is the minimum, otherwise the volume calculations of the spheres become too inaccurate. With a $fn=5 for example, your sphere volume calculations are almost a factor of 2 away from the analytical result.

$fn scales relatively linear to the calculation duration, by the way which sounds quite logical.

Regards,

Pete.

I believe that was a dash not minus.

https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Other_Language_Features#$fa,$fs_and$fn

If $fn <=0 then the $fa/$fs calculation is used.

From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of peter_osc@xs4all.nl
Sent: Thu, 13 Aug 2020 22:11
To: 'OpenSCAD general discussion'
Subject: Re: [OpenSCAD] Slow rendering performance and high memory consumption when exporting a 3D
STL

Hi Ron,

Results are here.

With $fn=-5, calculation duration decreases from 44 to 22 minutes. I don't know why.

I cannot find any documentation about negative $fn values though, except that its minimum value is
0.01.

By the way, I am benchmarking OpenSCAD/CGAL against FreeCAD/Opencascade here.

FreeCAD/OpenCascade does this job in less than a second and I don't see fundamental differences in
the STL files that are produced, except some minor differences in the placement of facets, and the
fact that FreeCAD produces a binary STL instead of ASCII.

So there is still a difference in performance of a factor of 1000 in this case which is worth
considering for me.

Below a screenshot of both designs in OpenSCAD and FreeCAD.

Pete.

From: Discuss discuss-bounces@lists.openscad.org On Behalf Of peter_osc@xs4all.nl
Sent: Thursday, August 13, 2020 13:32
To: 'OpenSCAD general discussion' discuss@lists.openscad.org
Subject: Re: [OpenSCAD] Slow rendering performance and high memory consumption when exporting a 3D
STL

Hi Ron,

Thanks for the advice.

$fn is related to the number of facets, so I cannot imagine that -5 is a legal value (although
OpenSCAD seems to accept $fn=-5 without warning. Waiting on the results though.).

Setting $fn=25 is the minimum, otherwise the volume calculations of the spheres become too
inaccurate. With a $fn=5 for example, your sphere volume calculations are almost a factor of 2 away
from the analytical result.

$fn scales relatively linear to the calculation duration, by the way which sounds quite logical.

Regards,

Pete.

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Hi Carsten,

Thanks for your work so far.

I was - indeed - mislead by the dash. Thanks MichaelAtOZ to point me on that one and sorry about that to everyone 😉

And yes, I also didn't consider that the intersection of a cuboid and about 100 spheres should take almost an hour (or more). It's a complex problem of raytracing but then again no so complex that it should take so many resources. In the final stage the problem could grow a factor of 10 to 100 larger and what happens then? A day? A Week?

What I still don't understand too is why this relatively simple problem peaks at 5 gigabytes.

Your compared it with AngelCAD. I also did a comparison with FreeCAD (OpenCascade) where this problem was also solved in a matter of seconds instead of hours. I even compared both resulting STLs but couldn't find any fundamental differences, except that the faceting in FreeCAD looks a bit different and has more faces. I included the FreeCAD Script.

For so far now the rendering for an STL benchmark results are:

FreeCAD: 1 second

AngelCAD: < 10 seconds

OpenSCAD: about 1 hour (depending on computer speed)

So the only thing that I can prove is that this specific problem can be solved 100 to 1000 times faster by two(?) other engines. But this is also fundamental to me because making cuboid intersections with complex bodies will one of the main applications.

Maybe one of the experts can clear out what's happening here and if there  are any workarounds? A performance difference in the order of magnitude of a factor of 100-1000 is too large to neglect.

And although the GUI rendering (F5, 1 second) is still very fast, the final rendering (F6, 42 minutes) doesn’t look very different to me on the screen.

And finally: As MichaelAtOz suggests, CGAL is the engine and also the cause of the behavior. CGAL contains an enormous and complex set of interoperable routines that cover a wide range of 2D and 3D problems. But might this complexity and versatility also cause overhead on basic functionality like raytracing to calculate CSG intersections, effectively slowing it down? Maybe I should (also) post this problem on the CGAL forum?

Pete.