[Sidefx-houdini-list] How to control RigidBody instances

Michael Dunkley mdunkley at gmail.com
Tue Nov 28 11:59:59 EST 2017


Hey Thomas - the null thing i mentioned isn't required per se, just
best practice and a very common houdini pattern.  Basically the idea
is you usually want to reference paths from nulls, if appropriate, so
that if your network graph changes (ie you add more relevant
operations after your wrangle), you don't have to change the
expression.  I guess the idea is that it makes your logic more
agnostic and less reliant on specific nodes.  My personal approach is
to label the nulls in ways that describe the state of the network at
that point (eg OUT_sim).   Again, not strictly necessary, just a
little cleaner than referencing workhorse nodes, and also works better
in cases where, for instance, you decide you want to cache the output
of your dop network before referencing it.
For your case i think the network would look something like
dop_import->null, and you'd then reference that null.

On Tue, Nov 28, 2017 at 11:14 AM, Thomas Volkmann <listmail.3d at gmail.com> wrote:
> Hi Michael, that works great! The shelf tools seem to do the packing
> automatically (copy stamp node).
> What do you mean by pulling from a null sop?
> So far I can point directly to /DopNetwork or use a merge node to get it
> inside my Geo where I connect it to the wrangle-node (was just about to
> test Oliviers approach when your mail came in...thanks Olivier I'll take a
> look at that approach in due time).
> It's a lot of these 'best practices' that I'm not aware of atm....
>
> cheers,
> Thomas
>
> On Tue, Nov 28, 2017 at 4:32 PM Michael Dunkley <mdunkley at gmail.com> wrote:
>
>> Hey Thomas.  So far as your expression goes - P is usually a point
>> attribute, not a detail, the detail function doesn't require "op"
>> syntax, and usually doesn't return an array unless you're asking for
>> an array attribute.
>> The expression you're looking for is probably more along the lines of:
>>
>> vector pos = point("/full_or_relative_path/to_node","P",3)
>>
>> where the path is just a normal houdini path, the attribute is
>> expressed as a string (as you had) and the 3 is simply the number of
>> the rbd you're trying to access.  This is making the assumption that
>> you're working with packed rbd's, so that the "point number" you're
>> grabbing actually represents an entire packed piece.  Unpacked rbd's
>> would be slightly trickier to grab.  Haven't watched that Entagma vid,
>> so i don't know which you're actually working with.
>> It would also be good practice to pull from a (null) sop if possible
>> (as opposed to dops directly - pulling directly from dops is certainly
>> possible, though the syntax is a little screwier and generally not
>> ideal).
>>
>>
>>
>> On Tue, Nov 28, 2017 at 9:05 AM, Olivier Jeannel <facialdeluxe at gmail.com>
>> wrote:
>> > I personnaly go with vop.
>> > Having the points you're working with in the first port.
>> > And the points you're gathering infos from in the second port.
>> > You can either use a PcOpen + Pcfilter (P) if you want to get the P
>> > according to the distance.
>> > Or use the Import Point (P) based on the id number.
>> >
>> > Or go the PrimUV route if you want to gather one attribute from polygon
>> > location (same as UV to Location in ICE)
>> >
>> >
>> > 2017-11-28 13:46 GMT+01:00 Thomas Volkmann <listmail.3d at gmail.com>:
>> >
>> >> A small follow-up:
>> >> How do I get the position of a certain RigidBody instance in another
>> >> objects pointwrangle?
>> >>
>> >> I'm trying:
>> >> vector pos[] = detail("op:/MyDOP/MyRBD_PackedObject", "P");
>> >>
>> >> Any hints?
>> >> Thanks,
>> >> Thomas
>> >>
>> >> On Mon, Nov 27, 2017 at 2:27 PM Thomas Volkmann <listmail.3d at gmail.com>
>> >> wrote:
>> >>
>> >> > Excellent, Thanks!
>> >> >
>> >> >
>> >> > On Mon, Nov 27, 2017 at 1:29 PM Matt Estela <matt.estela at gmail.com>
>> >> wrote:
>> >> >
>> >> >> Grow/shrinking is well covered by this entagma tutorial:
>> >> >>
>> >> >> http://www.entagma.com/scaling-the-bullets-dynamically/
>> >> >>
>> >> >>
>> >> >> On 27 November 2017 at 23:10, Thomas Volkmann <listmail.3d at gmail.com
>> >
>> >> >> wrote:
>> >> >>
>> >> >> > Hi,
>> >> >> >
>> >> >> > I'm taking another dive into Houdini again and I'm having a very
>> slow
>> >> >> start
>> >> >> > at the moment. It seems I have forgotten some of the basic
>> stuff....
>> >> >> > So if someone could help me out and save me a couple of hours it
>> would
>> >> >> be
>> >> >> > much appreciated.
>> >> >> >
>> >> >> > I have a simple RigidBody simulation from some instanced objects.
>> >> >> > Now I would like to do some stuff with some of these, like select
>> by
>> >> ID
>> >> >> and
>> >> >> > then putting them to sleep at a certain frame or have them
>> >> >> > growing/shrinking over time.
>> >> >> >
>> >> >> > Can I do that stuff all in the same place (some wrangle node /
>> where?)
>> >> >> or
>> >> >> > does the scaling has to happen in a sop and the sleep in the dop?
>> >> >> > Damn, I really thought I was past that initial confusion when
>> starting
>> >> >> with
>> >> >> > Houdini, but  a couple of months off seem to be a full reset on my
>> >> >> brain...
>> >> >> >
>> >> >> > Thanks,
>> >> >> > Thomas
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