Efficient generation of many PNG images from command line?

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,



--
Sent from: http://forum.openscad.org/

_______________________________________________
OpenSCAD mailing list
[hidden email]
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org

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 :-)



--
Sent from: http://forum.openscad.org/

_______________________________________________
OpenSCAD mailing list
[hidden email]
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org

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.




--
Sent from: http://forum.openscad.org/

_______________________________________________
OpenSCAD mailing list
[hidden email]
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org