thehans wrote

let me annote that hull() itself is not the problem. To avoid a time
consuming CGAL round trip, don't use (implicit) unions inside a hull(). If
you implement rounded_cube() more explicitely, rendering is fast (seconds).

$fa = 0.1;
$fs = 0.1;
rounded_cube_([4, 20, 5], r=1, center=[1,1,1]);

module rounded_cube_(size, r=0, center=false)
{
sz = size[0]==undef?[size, size, size]:size;
ce = center[0]==undef?[center, center, center]:center;
r_ = min(abs(r), abs(size.x/2), abs(size.y/2), abs(size.z/2));  // correct
r
translate([ce.x?-sz.x/2:0,ce.y?-sz.y/2:0, ce.z?-sz.z/2:0])
if(r)
hull()
{
translate([r_, r_, r_]) sphere(r_);
translate([r_, r_, sz.z-r_]) sphere(r_);
translate([r_, sz.y-r_, r_]) sphere(r_);
translate([r_, sz.y-r_, sz.z-r_]) sphere(r_);
translate([sz.x-r_, r_, r_]) sphere(r_);
translate([sz.x-r_, r_, sz.z-r_]) sphere(r_);
translate([sz.x-r_, sz.y-r_, r_]) sphere(r_);
translate([sz.x-r_, sz.y-r_, sz.z-r_]) sphere(r_);
}
else
cube(size);
}

in contrast the following call of hull will take minutes.

hull()
for(x=[r_,size.x-r_], y=[r_,size.y-r_], z=[r_,size.z-r_])
translate([x,y,z]) sphere(r_);

However, rounded_cube_ is currently a typical libary module. I wouldn't add
it to the core language unless cylinder(), linear_extrude() and maybe hull()
also get a r parameter.

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Sorry to be clueless, but why is it faster to enumerate the explicit
locations of the spheres vs having them in a loop?

Jon

On 1/30/2018 10:42 AM, Parkinbot wrote:

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On 1/30/2018 7:42 AM, Parkinbot wrote:

So you're saying it's better if the objects are simple and direct
children of the hull, rather than being a union (through whatever
mechanism) of those same objects?

JordanBrown wrote

Exactly. Have a look at the CSG structures. Results of a for loop are
represented as group node and processed as (implicit) union. And this needs
to be done by CGAL.

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Thank you Parkinbot!

This is an excellent example of how a user new to OpenSCAD could spin
their wheels "needlessly".  I know nothing about the internals of
OpenSCAD.  I imagine that most C programmers do not wish to have to
understand the details of the parser or the code generator.  I hope that
we can eventually have a tool where two seemingly identical structures
take roughly the same time to calculate.  I imagine there are good (and
subtle) reasons why this objective is difficult to achieve

Jon

On 1/30/2018 11:41 AM, Parkinbot wrote:

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I do not receive emails while away from my desk,
nor do I receive texts on my main phone number
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If you know that I am home, please email me.

Oh, wow.  I guess I had always assumed that hull was a CGAL operation.

You say this belongs in a library, but is there a single library that
has a properly implemented rounded cube?  Everyone's implementation is
different and 99.9% of them are slow and/or poduce ugly geometry.
This is why It should be standardized from the source.

I guess what I'm saying is at the very least MCAD should get updated
with an efficient module like you wrote here, because I think its
currently using what is more-or-less the same implementation as that
example006.scad I mentioned.
Also I should just say that my attention was originally drawn to
example006.scad a while ago when I was looking at improving OpenSCAD's
Travis build times, particularly in the execution time of individual
tests.  And example006.scad was one of the longest running tests.

Hans

On Tue, Jan 30, 2018 at 9:42 AM, Parkinbot rudolf@parkinbot.com wrote:

On 1/30/2018 8:41 AM, Parkinbot wrote:

Not knowing how hull( ) works, I wouldn't have expected there to be a
difference.

Good information, thanks.

I wonder if we could alleviate most of the slowdown of implicit union
by having group nodes do a simple bounding box check before passing to
CGAL, if no bounding boxes overlap then just skip it?

On Tue, Jan 30, 2018 at 10:49 AM, Jordan Brown
openscad@jordan.maileater.net wrote:

thehans wrote

Well I prefer libraries, which I write on my own, because they let me define
my own parameters and defaults and I can refer to the implementation. I
never understood why cube(), cylinder() and linear_extrude() are not
centered by default. And to be honest, I still don't know which prototypes
and defaults they exactly have. OK, this could be fixed by a proper
documentation ...

We have discussed it before several times that OpenSCAD is missing a
(standard) library concept. Have a look at the libraries folder shipped with
OpenSCAD and you will discover pretty old stuff that hasn't been maintained
for years.

See my implementation of a rounded_cylinder() and how it deals with
conflicts between diameters and radii. It is pretty fast, but I have no way
to figure out, whether it is semantically equivalent with cylinder,
therefore I can't call cylinder() with all its parameters in case r_ is 0.

$fa=.2;
$fs=.2;

CyR(r1=1, r2=6, h=7, r_=1.4, center = false);
//CyR(h=12, r_=1, r1=6, d2=1);

module CyR(r = 10, h=10, r_=1, d = undef, r1=undef, r2=undef, d1 = undef, d2
= undef, center=false)
{
r1 = r1==undef?d1==undef?d==undef?r:d/2:d1/2:r1;
r2 = r2==undef?d2==undef?d==undef?r:d/2:d2/2:r2;
r1_=min(abs(h/4), abs(r1), abs(r_));
r2_=min(abs(h/4), abs(r2), abs(r_));
echo(r1, r2, r1_, r2_);
h=abs(h);
translate([0,0,(center?-h/2:0)])
rotate_extrude()
intersection()
{
hull()
{
translate([r1-r1_, r1_]) circle(r1_);
translate([r2-r2_, h-r2_]) circle(r2_);
polygon([[0,0], [r1-r1_, r1_], [r2-r2_, h-r2_], [0,h]] );
}
square([max(r1,r2), h]);
}
}

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