inherit velocity RBD Packed Object

[ntkirby 4]

Hello everyone...  I have a problem with an RBD packed object inheriting velocity.  In the file, I have the attribute active being set by another object, but the velocity doesn't kick in at all.

The velocity works if I remove the point wrangle setting active to 0 and remove the sop solver.  
If I try a pop vop or a geo vop, there's some weird velocity behavior that happens.
If I tick on override attribute, the velocity takes off big time and doesn't appear that gravity takes hold.

All I'm looking for is initial velocity once the pieces become active.

I saw a few threads on the side fx forums and this forum, but nothing I saw seems to be working.

 

Any thoughts?

test_active_velocity.hipnc

[Dam 7]

Hello Neil,

Unfortunately something changes in the latest houdini versions about the inherit velocity from pack objects, a working way for inject the velocity only at the activation frame it's creating an attribute containing the previous @active value ($F-1), and add that to the "override attr from sop" inside the rbdpackedobject. That field should contain (@active and the created attribute containing the previous activation value ---> @prev_active) then with a geometry wrangle or pop wrangle it's possivle comparing the two attributes and gather the velocity to inject only if those two attribute are not the same with a point expression. I'm interested however if there are other ways for doing that, somebody have any idea?

--Cheers Dam

Edited September 18, 2017 by Dam

[Varishtraheja 0]

Hey I do not know if this is what you wanted but its still a cool tip. 

test_active_velocity_v002.hipnc

[ntkirby 4]

@Dam:  When I was looking at the spreadsheet in the DOP network, I noticed using the active attribute that the velocity was being reset as opposed to when I didn't explicitly define that attribute and using the sop solver...

@Varishtraheja:  Not what I wanted.  The animation needs to break apart like it's being affected by wind.  Look at this:  

 

[julian johnson 37]

Not sure I've understood your scene so take this with a pinch of salt. But, it looks like you're trying to transfer both the velocity attribute and the active attribute of the active object to the inactive ones. To do that I calculated the velocity on the active object using Trail SOP and then in the attribute transfer in the solver also transferred the velocity. Probably not what you meant!

test_active_velocity3.hipnc

[ntkirby 4]

@julian johnson

I looked at the file, it wasn't what I was looking for....for whatever reason, it's not keeping the initial velocity on the pieces when they are inactive.

I want the velocity to take off as the objects become active.  It doesn't matter whether I inherit velocity or even use the velocity on the rbd packed object to do it, it just won't do what I want.

Edited September 18, 2017 by ntkirby

[julian johnson 37]

Ah. OK, I think I now see what you mean.

Matt Estela's done a great example of what I think you mean here:

http://www.tokeru.com/cgwiki/index.php?title=HoudiniDops#RBD_inherit_.40v_and_.40w_after_initial_frame

I had a go on my own, too, and this seems to work as well.

test_active_velocity4.hipnc

[ntkirby 4]

@julian johnson - I saw the post here so I decided to try it.  It worked, so I went ahead and tried some other things outside of using wrangles to see what I could accomplish and I get some odd results.  I'll take a look at his H16 file and see if anything else is going on...I'll check yours too when I get home.

[cwhite 47]

For animated static objects you shouldn't need to do any extra work to transfer velocity:

https://www.sidefx.com/changelog/?journal=&categories=&body=inherit+velocity&version=16.0.491&build_0=&build_1=&show_versions=on&items_per_page=1

[ntkirby 4]

@cwhite 

I'm using 16.0.608
am I missing something though in my setup?  The active attribute starts at 0 and at some frame later changes to 1, but the velocity doesn't transfer.

[cwhite 47]

I think the object would also need to be marked as animated for the solver to fetch the updated value from SOPs

[ntkirby 4]

@cwhite - 
Thanks for the help, I tried to set the animated value but it didn't work out.  The solutions mentioned above worked out.

[julian johnson 37]

That's a great new feature. Far less elaborate than before. So, now as long as you set the initial state to active 0 and animated 1, you can switch to active at any time, turn off animated via attribute transfer in SOPS and the objects will inherit velocity at any frame.

test_active_velocity5.hipnc

[ntkirby 4]

Wow, ok...  so I just learned something new again

I apologize to @cwhite I just need to be properly educated

Thanks again @julian johnson

[dyei nightmare 7]

On 20/9/2017 at 7:07 AM, julian johnson said:

That's a great new feature. Far less elaborate than before. So, now as long as you set the initial state to active 0 and animated 1, you can switch to active at any time, turn off animated via attribute transfer in SOPS and the objects will inherit velocity at any frame.

test_active_velocity5.hipnc

 thats an elegant solution