My understanding is that OpenSCAD as currently constituted does not expose
the internals of objects, native or imported.

On Fri, Oct 21, 2022 at 10:22 AM fred via Discuss <
discuss@lists.openscad.org> wrote:

Thanks for the suggestions, I've temporarily solved half the problem,
simply write a file with my list of variables, in a text editor, or
generated by some other program, and include. So, instead of my
generating and formatting a text file, and copying/paste it in as a list
of points, I simply generate a valid scad file. Wood, trees, not seeing
comes to mind.

That file can be included wherever I want in the scad file, now to try
to find a way of saving data wherever I want e.g from within a module.

Virtually any programming language, maybe powershell, can create a line
like

seed=22102017152530;

based on the time, and save it as an scad file. It'll need to refresh
every second or so, however,  depending on needs.

On 21/10/2022 16:43, Father Horton wrote:

include<R:\Users\Ray\source\repos\timerapp\seeder>
echo (rands(0,10,2,9));
echo (rands(10,20,2));
echo (rands(20,30,2,ft));

The last random number pair can always be reseeded with a different
different seed (currently the ft seed is incremented every two seconds)
If it runs continuously, it;ll be about 15 years before it repeats.

-------- Forwarded Message --------
Subject: [OpenSCAD] Re: svg conversion in openscad
Date: Fri, 21 Oct 2022 17:46:41 +0100
From: Raymond West raywest@raywest.com
Reply-To: OpenSCAD general discussion Mailing-list
discuss@lists.openscad.org
To: discuss@lists.openscad.org

Thanks for the suggestions, I've temporarily solved half the problem,
simply write a file with my list of variables, in a text editor, or
generated by some other program, and include. So, instead of my
generating and formatting a text file, and copying/paste it in as a list
of points, I simply generate a valid scad file. Wood, trees, not seeing
comes to mind.

That file can be included wherever I want in the scad file, now to try
to find a way of saving data wherever I want e.g from within a module.

Virtually any programming language, maybe powershell, can create a line
like

seed=22102017152530;

based on the time, and save it as an scad file. It'll need to refresh
every second or so, however,  depending on needs.

On 21/10/2022 16:43, Father Horton wrote:

I'm not sure I understand your concerns about the random numbers.  With a
well-designed psueodrandom number generator, you're going to get
satisfactory outputs with a single seed.  If you are constantly reseeding
("increment the seed every two seconds") the most likely result of this is
that you will make the results less random.  Assuming the initializing is
good, you normally only need to worry about the seed if you need
repeatability, that is, if you specifically want to generate the same
sequence again.

There is no way to programmatically write data from OpenSCAD.  This is seen
as a security risk so I'm guessing it is unlikely to happen.  At risk of
repeating previous posts, I think there are libraries that will change SVG
to point lists, and there are OpenSCAD libraries that will parse SVG into a
point list, so you embed the SVG text content into your scad file.

On Fri, Oct 21, 2022 at 4:48 PM Raymond West raywest@raywest.com wrote:

On 10/21/2022 2:08 PM, Adrian Mariano wrote:

Mostly I agree with you, but OpenSCAD does behave perversely if you try
to mix non-repeatable random numbers (based on the internal timer+pid
entropy) with repeatable ones based on your custom seed.

The problem is that the PRNG isn't reseeded every run, and so your
second and successive runs all get the same sequence, because they are
all seeded from your (presumably fixed) last custom seed.

Try running this program repeatedly:

|echo(rands(0,1,1)); echo(rands(0,1,1,1));|

You would expect the first number to be "random" and the second number
to be fixed, but what actually happens is that they are both fixed
because on the second and subsequent runs, the first rands() call
generates the second value from the seed=1 sequence.

See issue #4391 https://github.com/openscad/openscad/issues/4391.

Generally, if you want to mix non-repeatable random numbers with
custom-seeded random numbers, you can do it by saving away one of the
non-repeatable numbers and setting it as the seed after you generate
your sequence of custom-seeded numbers.

function fixedRands(a, b, n, seed) =
    let (old = rands(0,1,1)[0])
    let (result = rands(a,b,n,seed))
    let (junk = rands(0,0,0,old))
    result;
echo(rands(0,1,1));
echo(fixedRands(0,1,1,1));
echo(rands(0,1,1));

will echo three numbers at a time, with the first and third varying from
run to run and the second remaining constant.  Of course, if you want to
generate multiple sets of your repeatable custom-seeded numbers, you
have to use different seeds.

This isn't a general save-restore mechanism, because the value returned
from rands() isn't the current seed, but if you were already on a
non-repeatable sequence, this leaves you on a non-repeatable sequence.

Caution: this is one of the few cases where you can tell that OpenSCAD
doesn't evaluate in the same order that most languages do.

save = rands(0,1,0);
junk1 = rands(0,1,1,1);
echo(rands(0,1,1));
junk2 = rands(0,0,1,save);

You might think that the number printed would be repeatable - it's based
off of the seed=1, isn't it?  Nope.  Assignments are all evaluated
before module calls, so all three assignments (save, junk1, junk2) are
evaluated before the echo() is evaluated.

Hi Adrian,

The random number concern was the fact that other languages that I have
used in the past could use a system timer for reseeding. I can do that
now, if i need to, within openscad. The two seconds is the approx time I
set for sleep in the external program to increment the seeder code. I
will probably never need it, but it was an easy example to set up.

In the past I had written external code to import, manipulate or
generate svg code, and save it such that openscad could import the
changed svg.  Now I can import the svg as a list of points, or whatever,
more or less anywhere in the openscad script.

I'm not sure what security risk is created by exporting a list of
numbers from within openscad. A risk to who, or what? As it is, openscad
exports/imports it's own version of svgs and dxfs, which leads to errors
in other programs, so I can't see a list of numbers  generated by the
user's scripting  as being any more risky.

Best wishes,

Ray

On 21/10/2022 22:08, Adrian Mariano wrote:

The only reason you'd want to reseed based on the clock is the one Jordan
mentioned, that you need to mix repeatable and non-repeatable number
streams.

I'm just reporting what I've read in the past on this forum:  if you can't
write to the disk you can't cause harm.  If you can write to the disk,
maybe you can.  Maybe you obliterate some important file with numbers and
it causes problems.  Maybe there's an openscad bug that lets you cause it
to write something else.  Basically, it creates a possibility that isn't
otherwise present.

On Fri, Oct 21, 2022 at 7:20 PM Raymond West raywest@raywest.com wrote:

On 10/21/2022 4:18 PM, Raymond West wrote:

You're a Linux user, right?  Suppose that we had a module
export(filename, value) that writes the specified value to the specified
file.

export(".profile", [0]);

... destroys the user's login script, if they run OpenSCAD in their home
directory.

for (i=[1:999999], j=[1:999999]) export(str(i,"-",j), [0]);

fills up the user's disk by creating ~10^12 files in the current directory.

There's a big difference between allowing the user to save the output
from the program to a file of their choice, and allowing the program to
save data to a name of its choice without the user's intervention.

One could easily imagine having a user action "save the log from the
last run" - but that would be the user taking an action and controlling
the name of the file to be written.