Cannot Difference Multiple Module Instances
I am attempting to use difference() to subtract 2 instances of a module for another instance of the module. It works fine when subtracting only one instance, but subtracting 2 does not work. For example:
//The following works fine:
difference(){
MyModule();//Instance One
MyModule();}//Instance Two
//The following works fine:
difference(){
MyModule();//Instance One
MyModule();}//Instance Three
//The following does not work:
difference(){
MyModule();//Instance One
MyModule();//Instance Two
MyModule();}//Instance Three
The last of the above examples gives the following output:
Compiling design (CSG Tree generation)...
Compiling design (CSG Products generation)...
Geometries in cache: 1277
Geometry cache size in bytes: 14822752
CGAL Polyhedrons in cache: 6
CGAL cache size in bytes: 93491736
Compiling design (CSG Products normalization)...
WARNING: Normalized tree is growing past 200000 elements. Aborting normalization.
WARNING: CSG normalization resulted in an empty tree
Normalized tree has 0 elements!
Compile and preview finished.
Total rendering time: 0:00:00.209
I'm not sure how to figure out what the problem is, since all the instances work individually, and can be subtracted individually. What should I do?
Nathan Sokalski
njsokalski@hotmail.commailto:njsokalski@hotmail.com
Nathan Sokalski wrote:
//The following does not work:
difference(){
MyModule();//Instance One
MyModule();//Instance Two
MyModule();}//Instance Three
Don’t quite see the point in subtracting MyModule from MyModule, but
difference()
{
module one();
module two();
module three();
}
Subtracts two and three from one. If you want to subtract three from one and two, it needs a union:
difference()
{
union()
{
module one();
module two();
}
module three();
}
Sorry for the misunderstanding, what I submitted was just to show that I was using difference (my actual modules are obviously much more complex & have multiple parameters, so the instances would not all be the same like in my post). The problem I am having only occurs when I am subtracting 2 elements (which is why the difference() that does not work is the one with 3 children)
Nathan Sokalski
njsokalski@hotmail.commailto:njsokalski@hotmail.com
From: mikeonenine@web.de mikeonenine@web.de
Sent: Friday, August 18, 2023 1:16 AM
To: discuss@lists.openscad.org discuss@lists.openscad.org
Subject: [OpenSCAD] Re: Cannot Difference Multiple Module Instances
Nathan Sokalski wrote:
//The following does not work: difference(){ MyModule();//Instance One MyModule();//Instance Two MyModule();}//Instance Three
Don’t quite see the point in subtracting MyModule from MyModule, but
difference()
{
module one();
module two();
module three();
}
Subtracts two and three from one. If you want to subtract three from one and two, it needs a union:
difference()
{
union()
{
module one();
module two();
}
module three();
}
On 8/18/23 00:35, Nathan Sokalski wrote:
I am attempting to use difference() to subtract 2 instances of a module
for another instance of the module. It works fine when subtracting only
one instance, but subtracting 2 does not work. For example:
//The following works fine:
difference(){
MyModule();//Instance One
MyModule();}//Instance Two
//The following works fine:
difference(){
MyModule();//Instance One
MyModule();}//Instance Three
//The following does not work:
difference(){
MyModule();//Instance One
MyModule();//Instance Two
MyModule();}//Instance Three
The last of the above examples gives the following output:
Compiling design (CSG Tree generation)...
Compiling design (CSG Products generation)...
Geometries in cache: 1277
Geometry cache size in bytes: 14822752
CGAL Polyhedrons in cache: 6
CGAL cache size in bytes: 93491736
Compiling design (CSG Products normalization)...
WARNING: Normalized tree is growing past 200000 elements. Aborting
normalization.
WARNING: CSG normalization resulted in an empty tree
Normalized tree has 0 elements!
Compile and preview finished.
Total rendering time: 0:00:00.209
I'm not sure how to figure out what the problem is, since all the
instances work individually, and can be subtracted individually. What
should I do?
Nathan Sokalski
njsokalski@hotmail.com mailto:njsokalski@hotmail.com
Nathan: In edit>preferences>advanced, you need to set bigger buffers.
Some of this can use huge amounts of memory. I'm doing even more complex
stuff and I've set buffers to use the 32G's in this machine. If your box
doesn't have the memory it can use swap but swap gets slow. I'm set for
100G of swap. I'm also using the latest AppImage in linux, available
from the far bottom of the home page, much faster that the 2 yo release.
Cheers, Gene Heskett.
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page http://geneslinuxbox.net:6309/
On 8/17/2023 9:34 PM, Nathan Sokalski wrote:
WARNING: Normalized tree is growing past 200000 elements. Aborting
normalization.
On its face, OpenSCAD is complaining that your model is too complex. Is
it a complex model? Try making it less complex, to see if that makes
the problem go away. (I understand that it likely as complex as it
needs to be, but for diagnostic purposes try stripping stuff out.)
When you preview one instance of your module, how many nodes are in the
tree? Look for
Normalized tree has 2 elements!
in the console pane. Does the number make sense for what you're trying
to do? If it reports you have thousands of nodes, and you know that you
have thousands of individual pieces, fine, but if you think you only
have a handful of pieces but it reports thousands, maybe there's a bug.
Is the number in the high tens of thousands? With a limit of 200,000,
three modules with more than ~66K nodes each would exceed the limit.
Can you share the program?
On Thu, Aug 17, 2023, 11:35 PM Nathan Sokalski njsokalski@hotmail.com
wrote:
WARNING: Normalized tree is growing past 200000 elements. Aborting
normalization.
WARNING: CSG normalization resulted in an empty tree
First things first, you can go to Preferences -> Advanced -> Turn off
rendering at _____ elements, and increase the value there.
The limit is meant to help curb exploding memory usage under certain
circumstances, but if you have the memory for it then it doesn't hurt to
add a zero or two.
What this means: OpenCSG requires the boolean geometry expression to be in
a "Sum of Products" form aka disjunctive normal form (DNF).
That's what the "Design" -> "Display CSG Products" menu entry refers to,
and you can see how that goes together. Converting an arbitrary boolean
expression to DNF, in the worst case, can balloon to 2^N terms.
Where N is the number of geometry nodes originally in the CSG Tree.
This is loosely related to the well known computer science problem of
Boolean Satisfiability (SAT) which is NP hard.
There is also some mention of the issue in this FAQ entry:
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/FAQ#Why_is_the_preview_so_slow
?
To reduce these number of terms you can wrap some of your inner nested
boolean operations in render() { ... }
This effectively will convert that subtree of operations into a single
geometry leaf node, which simplifies the normalization stage of preview.
This will cause preview to take some extra time initially, but will greatly
help the draw times (per frame, when orbiting camera etc.).
It is best to do this on parts involving boolean operations, which have low
to medium geometry complexity, but are possibly repeated often in the
overall composition.
Hope that helps.