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Tumbling Instanced particles

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tim
Tumbling Instanced particles
by
on Oct 10, 2007 at 6:08:29 pm

Hey Yall,
I found a few posts instructing how to make instanced particles rotate but I am unfamiliar with some of the terminology etc. I was hoping someone could explain it a little clearer for a novice.

Thanks in advance.


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tim
Re: Tumbling Instanced particles
by
on Oct 11, 2007 at 11:47:56 am

anyone? steve?


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Steve Sayer
Re: Tumbling Instanced particles
on Oct 11, 2007 at 7:20:37 pm

Uh-oh: now I'm getting personal requests? :P

Sorry, I've been busy this week!

Controlling the rotation of instanced particles has always been a bit of a hassle, and Maya's documentation in this area has been poor. The Attribute Editor is even a bit buggy, or at least was in previous versions; perhaps it has been fixed since.

In general, particles don't by default have 'rotate' channels. We therefore have to manufacture some rotation information for them when we instance objects to them.

One of the parts that will trip you up is the difference between 'aim' and 'rotation'. The most common thing to do is to make instanced objects point along the trajectory of the particle, which involves controlling them using the 'aim' method (and setting it to 'velocity,' if I recall correctly). On the other hand, if you want to tumble the instanced objects randomly, it might be more appropriate to use the 'rotate' strategies to control rotation explicitly.

It's tough to give a general overview; what is the specific task you are trying to accomplish?

-Steve


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tim
Re: Tumbling Instanced particles
by
on Oct 11, 2007 at 9:04:01 pm

yeah, i have noticed that you seem to be the one always responding to the particle questions. =) basically i just want the particles to rotate randomly as they emit.

this is another place im looking for the answer, and i think its on the right track but as you can see i hit another snag...
http://www.highend3d.com/boards/index.php?showtopic=240064

thanks


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Steve Sayer
Re: Tumbling Instanced particles
on Oct 11, 2007 at 10:28:06 pm

I think the snag you hit is that something went wrong while adding the custom per-particle attribute.

Look at the particleShape node in the Attribute Editor. In the section 'Per Particle (Array) Attributes' you should have your 'rotPP' attribute listed. If it's not there, click on the 'General' button in the 'Add Dynamic Attributes' section. Make sure you choose 'vector' for the Data Type and 'Per Particle' for the Attribute Type. Name it rotPP and it should work out...

Good luck.

-Steve


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tim
Re: Tumbling Instanced particles
by
on Oct 12, 2007 at 12:12:57 pm

I remade the attribute very carefully, but I am still getting "// Error: Attribute not found or variable missing '$': particleShape1.gbwRotates"

What is the missing variable $ all about. I really think that is what is doing it. Ideas?



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Steve Sayer
Re: Tumbling Instanced particles
on Oct 13, 2007 at 3:32:25 pm

No, the variable warning is unrelated; Maya always suggests that when it comes across a piece of text it doesn't recognize. If you're sure you added the attribute to the particle SHAPE node, and that you created it as a dynamic (per-particle) attribute, and matched its name with the name in the expression... then I'm out of ideas! Can you upload the scene file (as Maya ASCII)?

-Steve


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tim
Re: Tumbling Instanced particles
by
on Oct 13, 2007 at 4:09:53 pm

Well i tried it again to no success. How would I go about uploading the file? Can I do that here or must I do it on some outside source? I could email if you want. Whatever is most convenient for you. Let me know.

Again, thanks for all the help!


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Steve Sayer
Re: Tumbling Instanced particles
on Oct 13, 2007 at 6:01:24 pm

You can upload it to an external host, or email it to me.

My address is steve at stephensayer dot com.

-Steve


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tim
Re: Tumbling Instanced particles
by
on Oct 15, 2007 at 11:18:57 am

Ok so Steve has been tremendously helpful. He gave me this other expression that works great.


Creation: PGD2_partsShape.rotPP = sphrand(<<1,1,1>>);
Runtime: PGD2_partsShape.rotPP += <<5,5,5>>;

I still am unsure why the other one did not work but this one seems a lot simpler anyway.

Thanks Steve!


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