Efficient generation of many PNG images from command line?

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Efficient generation of many PNG images from command line?

Vigardo
Dear experts,

I need to generate hundreds (if not thousands) of views from a single
OpenSCAD model using just the command line tool (because it will run on a
linux web server), and as fast as possible. So far, I´ve only found an old
thread about this topic titled " rendering scad images via an api
<http://forum.openscad.org/rendering-scad-images-via-an-api-td4277.html>  ",
but the issue was not fully solved.

I already can do it using the -D option to pre-define some variable(s), for
example with the following bash script:

for((i=0;i<=100;i++))
do
  openscad -o myimage_$i.png --imgsize=640x480 --autocenter --projection o
--camera 0,0,0,90,0,0,10 -D someangle=$i -q mymodel.scad
done

This approach is terribly slow (minutes) because OpenSCAD parses the input
scad file and renders the scene for every single view. Any better
alternatives?

I know that OpenSCAD GUI is able to dump all animation images, but this
option seems not available from command line. Perhaps, adding an
"--animation" option would be a good improvement in future releases, don´t
you think?

Ideally, OpenSCAD would read once the input model and then generate and dump
the PNG image for every pre-defined variable set. Such variable sets would
be provided via some simple text file with, e.g. one variable set per line.
Note that, at least for my application, the model is the same for all
generated views, only the orientation changes.

Thanks a lot in advance!



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Re: Efficient generation of many PNG images from command line?

tp3
On 09.01.21 12:54, Vigardo wrote:
> I know that OpenSCAD GUI is able to dump all animation images,
> but this option seems not available from command line. Perhaps,
> adding an "--animation" option would be a good improvement in
> future releases, don´t you think?

Yep, that already exists in the release candidates.

In addition there's a persistent cache feature which is still
work in progress. As the name implies, this will persist caches
across multiple separate calls of OpenSCAD via either local
files or redis server.

ciao,
  Torsten.

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Re: Efficient generation of many PNG images from command line?

Vigardo
Sorry for my ignorance or if I did not understood you well:

1) Then, is the  OpenSCAD release candidate 2021.01-RC5 (6 January 2021)
<https://www.openscad.org/news.html>  , available as a Development Snapshots
in the  downloads page <https://www.openscad.org/downloads.html>   able to
dump all animation PNGs from the command line?

2) Will the persistent cache feature persist across multiple separate calls
to OpenSCAD command-lined or just the GUI version?

3) When do you think such persistent cache will be available?

Thanks a lot for the help and quick response!



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Re: Efficient generation of many PNG images from command line?

tp3
On 09.01.21 18:10, Vigardo wrote:
> 1) Then, is the  OpenSCAD release candidate 2021.01-RC5
> (6 January 2021) <https://www.openscad.org/news.html>,
> available as a Development Snapshots in the downloads
> page <https://www.openscad.org/downloads.html> able to
> dump all animation PNGs from the command line?

At this point dev snapshots and the release candidate
are almost identical but that will start to diverge
again pretty soon. Both support the new --animate
command line option.

Downloads are separate:
RC: https://www.openscad.org/downloads.html#rc
DEV: https://www.openscad.org/downloads.html#snapshots

> 2) Will the persistent cache feature persist across
> multiple separate calls to OpenSCAD command-lined or
> just the GUI version?

It's supposed to work with both (but commandline will
need explicit setup options, not using the config that
is available in GUI).

> 3) When do you think such persistent cache will be
> available?
No idea. I'd love to see that as soon as possible, but
there's no way to plan free time of people.

ciao,
  Torsten.

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Re: Efficient generation of many PNG images from command line?

Troberg
In reply to this post by Vigardo
I have a similar problem, though with SVG export. Just having to restart
everything for every export takes ages. Animation doesn't work for anything
but PNG.

It would be great if there was a built-in export (filename) module.

Example:

export("mypart.svg")
mypart();



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Re: Efficient generation of many PNG images from command line?

tp3
On 09.01.21 20:11, Troberg wrote:
> I have a similar problem, though with SVG export. Just
> having to restart everything for every export takes ages.
> Animation doesn't work for anything but PNG.

It does work in command line mode.

--- square.scad ---
rotate(90 * $t) square(10);
-------------------

openscad-nightly --animate 10 -o square.svg square.scad

produces 10 SVG files with a rotating square, although it
might be useful to also add a camera option too for a
fixed view.

> export("mypart.svg")
> mypart();

No. There's likely some feature to export multiple files,
but it's not going to be an imperative call writing a file.

ciao,
  Torsten.

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Re: Efficient generation of many PNG images from command line?

JordanBrown
On 1/9/2021 11:39 AM, Torsten Paul wrote:
No. There's likely some feature to export multiple files, but it's not going to be an imperative call writing a file.

Indeed.  Danger, Will Robinson!  As soon as the language has a way to write named files, you have to worry about what interesting files a malicious program might write.

(That's one of the disturbing aspects of a Python-based replacement, that it's hard to avoid giving the program you just downloaded way too much access to your system.)


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Re: Efficient generation of many PNG images from command line?

Troberg
In reply to this post by tp3
> > I have a similar problem, though with SVG export. Just
> > having to restart everything for every export takes ages.
> > Animation doesn't work for anything but PNG.
>
> It does work in command line mode.

Wow, didn't know that! Now I'll have to rethink my 11 hour export batch!

> produces 10 SVG files with a rotating square, although it
> might be useful to also add a camera option too for a
> fixed view.

Not really, as the SVG files will be top down of the entire object, no
matter what, which is what I like.

> > export("mypart.svg")
> > mypart();
>
> No. There's likely some feature to export multiple files,
> but it's not going to be an imperative call writing a file.

So, just don't allow any directory except the same as the SCAD file. Can't
do much damage then, unless the user does something really, really stupid,
such as running it from the Windows directory.

Or just have a setting to turn off all file writing in the settings, which
is set to disable as default.

For me, it would be immensely useful to be able to write to files, both as
export and as an ability to echo() to a file. It makes it much easier to
build an integrated tool chain where you can connect everything with little
or no manual interaction.



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Re: Efficient generation of many PNG images from command line?

tp3
On 10.01.21 08:06, Troberg wrote:
>> produces 10 SVG files with a rotating square, although it
>> might be useful to also add a camera option too for a
>> fixed view.

> Not really, as the SVG files will be top down of the entire
> object, no matter what, which is what I like.

Right, I was thinking of PNG where the camera does define
the field of view. I think you are correct that it would
not have an effect on the viewport of the SVG. Some other
workaround like tiny boxes in the viewport corners might
work.

ciao,
  Torsten.


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Re: Efficient generation of many PNG images from command line?

goblinbot
In reply to this post by Vigardo
You can get pretty good speed boost, at least with Linux.  You can add a space and ampersand at the end of the commands your script is making.  That will launch that command in a separate thread, so you'll have multiple instances of openscad running simultaneously.  Depending on how many cores your computer has, you should get a pretty good reduction in processing time.  You have to add a 'wait' command at the end for the script to wait for all the threads to finish.

On January 9, 2021 6:55:32 AM Vigardo <[hidden email]> wrote:

Dear experts,

I need to generate hundreds (if not thousands) of views from a single
OpenSCAD model using just the command line tool (because it will run on a
linux web server), and as fast as possible. So far, I´ve only found an old
thread about this topic titled " rendering scad images via an api
<http://forum.openscad.org/rendering-scad-images-via-an-api-td4277.html>  ",
but the issue was not fully solved.

I already can do it using the -D option to pre-define some variable(s), for
example with the following bash script:

for((i=0;i<=100;i++))
do
  openscad -o myimage_$i.png --imgsize=640x480 --autocenter --projection o
--camera 0,0,0,90,0,0,10 -D someangle=$i -q mymodel.scad
done

This approach is terribly slow (minutes) because OpenSCAD parses the input
scad file and renders the scene for every single view. Any better
alternatives?

I know that OpenSCAD GUI is able to dump all animation images, but this
option seems not available from command line. Perhaps, adding an
"--animation" option would be a good improvement in future releases, don´t
you think?

Ideally, OpenSCAD would read once the input model and then generate and dump
the PNG image for every pre-defined variable set. Such variable sets would
be provided via some simple text file with, e.g. one variable set per line.
Note that, at least for my application, the model is the same for all
generated views, only the orientation changes.

Thanks a lot in advance!



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Re: Efficient generation of many PNG images from command line?

Troberg
goblinbot wrote
> You can get pretty good speed boost, at least with Linux.  You can add a
> space and ampersand at the end of the commands your script is making.
> That
> will launch that command in a separate thread, so you'll have multiple
> instances of openscad running simultaneously.  Depending on how many cores
> your computer has, you should get a pretty good reduction in processing
> time.  You have to add a 'wait' command at the end for the script to wait
> for all the threads to finish.

Well, I run them in Windows (my most powerful machine, hardware wise, is a
Windows machine, as I also use it for gaming), from my own program. I could
simply launch several instances from that program, but the downside is that
it bogs down the computer too much, as Windows is really crappy at
starting/stopping programs in an intelligent and efficient way, so your OS
gets mutex-strangled.



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Re: Efficient generation of many PNG images from command line?

Vigardo
Thank you all for the interesting comments!

*goblinbot*: I already was aware of the "& + wait" parallelization, nice
contribution anyways!

*tp3*: I´ve tried some dummy example to generate several views of a rotating
model using either successive command line calls to OpenSCAD or a single
call with the --animate option. The latter resulted about 2-fold faster (23
s vs 40 s).

To test this I used the following command

#> time /home/mon/OpenSCAD-2021.01-RC6-x86_64.AppImage --animate 37
--colorscheme Tomorrow --camera 0,0,0,90,0,0,5 anim.scad

and the following OpenSCAD script:

// Explicit rotation
echo("a=",$t*180);
rotate(a=$t*180,v=[0,0,1]) mymodel();

module mymodel()
{    
    difference()
    {
        cube([1,1,1],center=true);
        sphere(d=1.25,$fn=24);
    }
}

Now I wonder if there would be a faster approach, for example, to rotate the
camera (using --camera option) or the viewport (using $vpr) instead of the
direct model rotation.

// Viewport rotation
$vpr=[90,0,-$t*180];
echo("vpr=",$vpr,"vpt=",$vpt,"vpd=",$vpd);
mymodel();

However, using the following command (with or without the --camera option)
produces a very small object.

#> time /home/mon/OpenSCAD-2021.01-RC6-x86_64.AppImage --animate 37
--colorscheme Tomorrow --camera 0,0,0,90,0,0,5 anim.scad

ECHO: "vpr=", [90, 0, -34.0541], "vpt=", [0, 0, 0], "vpd=", 500

I only partially fix this behavior by explicitly setting the $vpd variable
to a manually adjusted value, e.g. 5.

#> time /home/mon/OpenSCAD-2021.01-RC6-x86_64.AppImage --animate 37
--colorscheme Tomorrow -D '$vpd=5' anim.scad

Unfortunately, there was not any significant speedup using $vpr rotation.

In any case, this behavior (having to manually set the $vpd value) differs
from GUI and is quite annoying since in GUI there is no need to specify the
$vpd variable at all.

1) I think that the command line tool should behave exactly the same as the
GUI version, at least for this case, don´t you agree?

2) Any faster approach to generate different views from a model in OpenSCAD?
Intuitively it seems that computing a thousand views should take just a
couple of seconds (the 3D navigation is very responsive) but it takes around
10 times more, why is this so?

Best,



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Re: Efficient generation of many PNG images from command line?

nophead
Animation recomputes everything as any aspect of the geometry could depend on $t, not just the camera position.

You do set $vpd in the GUI with the zoom setting and it is displayed as "distance" in the status bar.

On Tue, 19 Jan 2021 at 20:12, Vigardo <[hidden email]> wrote:
Thank you all for the interesting comments!

*goblinbot*: I already was aware of the "& + wait" parallelization, nice
contribution anyways!

*tp3*: I´ve tried some dummy example to generate several views of a rotating
model using either successive command line calls to OpenSCAD or a single
call with the --animate option. The latter resulted about 2-fold faster (23
s vs 40 s).

To test this I used the following command

#> time /home/mon/OpenSCAD-2021.01-RC6-x86_64.AppImage --animate 37
--colorscheme Tomorrow --camera 0,0,0,90,0,0,5 anim.scad

and the following OpenSCAD script:

// Explicit rotation
echo("a=",$t*180);
rotate(a=$t*180,v=[0,0,1]) mymodel();

module mymodel()
{   
    difference()
    {
        cube([1,1,1],center=true);
        sphere(d=1.25,$fn=24);
    }
}

Now I wonder if there would be a faster approach, for example, to rotate the
camera (using --camera option) or the viewport (using $vpr) instead of the
direct model rotation.

// Viewport rotation
$vpr=[90,0,-$t*180];
echo("vpr=",$vpr,"vpt=",$vpt,"vpd=",$vpd);
mymodel();

However, using the following command (with or without the --camera option)
produces a very small object.

#> time /home/mon/OpenSCAD-2021.01-RC6-x86_64.AppImage --animate 37
--colorscheme Tomorrow --camera 0,0,0,90,0,0,5 anim.scad

ECHO: "vpr=", [90, 0, -34.0541], "vpt=", [0, 0, 0], "vpd=", 500

I only partially fix this behavior by explicitly setting the $vpd variable
to a manually adjusted value, e.g. 5.

#> time /home/mon/OpenSCAD-2021.01-RC6-x86_64.AppImage --animate 37
--colorscheme Tomorrow -D '$vpd=5' anim.scad

Unfortunately, there was not any significant speedup using $vpr rotation.

In any case, this behavior (having to manually set the $vpd value) differs
from GUI and is quite annoying since in GUI there is no need to specify the
$vpd variable at all.

1) I think that the command line tool should behave exactly the same as the
GUI version, at least for this case, don´t you agree?

2) Any faster approach to generate different views from a model in OpenSCAD?
Intuitively it seems that computing a thousand views should take just a
couple of seconds (the 3D navigation is very responsive) but it takes around
10 times more, why is this so?

Best,



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Re: Efficient generation of many PNG images from command line?

Vigardo
Thanks *nophead* for the quick response!

What you say makes sense: "Animation recomputes everything as any aspect of
the geometry could depend on $t, not just the camera position."

But, what if the model does not change at all and what just changes is
camera view? Recomputing everything in this case seems a waste of CPU time,
don´t you agree?

Is there a way to speed up the generation of different view snapshots of
exactly the same object?

(Sorry if I say something stupid since I don´t know how OpenSCAD internally
works :-)



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Re: Efficient generation of many PNG images from command line?

nophead
Yes in theory it could be optimised but since $vpr, etc are just variables anything could depend on them, so it would need a compex dependency analysis to work out that none of the model had changed.

Sprinkling render() in the model might help because then the geometry gets computed once and cashed, so each animation frame would only calculate all the variables and expressions and get cache hits for all the geometry.


On Thu, 21 Jan 2021 at 17:59, Vigardo <[hidden email]> wrote:
Thanks *nophead* for the quick response!

What you say makes sense: "Animation recomputes everything as any aspect of
the geometry could depend on $t, not just the camera position."

But, what if the model does not change at all and what just changes is
camera view? Recomputing everything in this case seems a waste of CPU time,
don´t you agree?

Is there a way to speed up the generation of different view snapshots of
exactly the same object?

(Sorry if I say something stupid since I don´t know how OpenSCAD internally
works :-)



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Re: Efficient generation of many PNG images from command line?

lar3ry
nophead wrote
> Yes in theory it could be optimised but since $vpr, etc are just variables
> anything could depend on them, so it would need a compex dependency
> analysis to work out that none of the model had changed.

I wonder how many folks would use simple camera movements, without any need
for re-rendering.
If there's a significant number who wish for it, perhaps OpenSCAD could
include some sort of switch that would turn that on as a specific mode. I
know I have wanted to send someone a single animated file rather than a
series of PNGs in order to show different aspects of a model. I never
bothered, because doing so took too long.

It wouldn't even be necessary to detect things that would require
re-rendering, if a warning about bad results could occur.




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Re: Efficient generation of many PNG images from command line?

nophead
The problem is the camera parameters are set with variables, which can depend on any other variables or expressions. So you have to at least run the first pass of OpenSCAD that evaluates all the expressions. That is usually quick but can get very slow. In my case it takes minutes.

When it is animating, which stage takes all the time? I.e. 

Parsing design (AST generation)...

Compiling design (CSG Tree generation)...

Compiling design (CSG Products generation)...

Compiling design (CSG Products normalization)...


On Thu, 21 Jan 2021 at 19:16, lar3ry <[hidden email]> wrote:
nophead wrote
> Yes in theory it could be optimised but since $vpr, etc are just variables
> anything could depend on them, so it would need a compex dependency
> analysis to work out that none of the model had changed.

I wonder how many folks would use simple camera movements, without any need
for re-rendering.
If there's a significant number who wish for it, perhaps OpenSCAD could
include some sort of switch that would turn that on as a specific mode. I
know I have wanted to send someone a single animated file rather than a
series of PNGs in order to show different aspects of a model. I never
bothered, because doing so took too long.

It wouldn't even be necessary to detect things that would require
re-rendering, if a warning about bad results could occur.




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Re: Efficient generation of many PNG images from command line?

Vigardo
Thanks all for the interesting contributions and fast responses, you´re very
nice!

The render() parameter does speed up the process more than 10 fold (i.e.
from about 20 to less than 2 seconds!) using either the "Explicit rotation"
or the "Viewport rotation" methods.

However, this only works from GUI. When I run it from command-line "Explicit
rotation" works but takes 20 s and the "Viewport rotation" takes the same
time but the view is not updated (i.e. 36 equal "frozen" snapshots are
produced...). Is this the expected OpenSCAD behavior?

I think that *tp3* already advised about this on a previous post:

Me: "2) Will the persistent cache feature persist across multiple separate
calls to OpenSCAD command-lined or just the GUI version?"
tp3: "It's supposed to work with both (but command line will need explicit
setup options, not using the config that is available in GUI)."

What are these "explicit setup options"?

For completeness, these were the two methods used in my tests:

// Explicit rotation
echo("a=",$t*180);
rotate(a=$t*180,v=[0,0,1])
    render()
         mymodel();

// Viewport rotation
$vpr=[90,0,-$t*180];
$vpd=5;
echo("vpr=",$vpr,"vpt=",$vpt,"vpd=",$vpd);
render()
    mymodel();

And this was the command:

#> time OpenSCAD-2021.01-RC6-x86_64.AppImage --animate 36 --camera
0,0,0,90,0,0,5 ViewRender.scad

Note that the --camera option is required to prevent the annoying automatic
zoom in & out issue. I want that the object appears like if it were placed
in a virtual rotation table, the camera has to be at the same distance all
the time.

By the way, is there some way to tell OpenSCAD to use the initial camera
parameters (i.e. those at $t=0) for the whole animation?



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Re: Efficient generation of many PNG images from command line?

JordanBrown
On 1/22/2021 9:43 AM, Vigardo wrote:
// Explicit rotation
echo("a=",$t*180);
rotate(a=$t*180,v=[0,0,1]) 
    render()
         mymodel();

// Viewport rotation
$vpr=[90,0,-$t*180];
$vpd=5;
echo("vpr=",$vpr,"vpt=",$vpt,"vpd=",$vpd);
render()
    mymodel();

You probably want to stick with the latter.  It's doing what you want to do:  moving the camera.

And this was the command:

#> time OpenSCAD-2021.01-RC6-x86_64.AppImage --animate 36 --camera
0,0,0,90,0,0,5 ViewRender.scad

Note that the --camera option is required to prevent the annoying automatic
zoom in & out issue. I want that the object appears like if it were placed
in a virtual rotation table, the camera has to be at the same distance all
the time.

I'm not sure exactly what problem you're seeing, but note that --camera is the same as setting $vpt, $vpr, and $vpd.

By the way, is there some way to tell OpenSCAD to use the initial camera
parameters (i.e. those at $t=0) for the whole animation?

Don't have $vpt/$vpr/$vpd depend on $t.  Or is there something more complicated that I'm missing?

But of course if your animation consists of flying your camera around, it will get really boring if you don't have the camera move when $t changes.


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Re: Efficient generation of many PNG images from command line?

Whosawhatsis
In reply to this post by Vigardo
On Jan 22, 2021, 09:44 -0800, Vigardo <[hidden email]>, wrote:
#> time OpenSCAD-2021.01-RC6-x86_64.AppImage --animate 36 --camera
0,0,0,90,0,0,5 ViewRender.scad

Putting --camera in your command line will override $vpr, $vpt and $vpd.

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