Attributes general questions

[pyroskat]

Hi guys. I'm new on Houdini, 3 days doing tutorials (10 hours per day), I'm coming from 3dsmax-Thinking Particles. Attributes are cool, but there are some thinks that I can't figure out how to do it:

-Create an attribute that comes from another variable attribut but fixed in time: For example I have a create surface volume, I added create attribute and I want a new attribute that takes the initial values of $TY. If I simple add $TY on the first frame is ok, but when particles move going down they change this new atribute in funtion of his position (as expected). The question is: can I create an attribute that takes the value of TY but only on the first frame? so its fixed even when particle change his position?

-If I turn off my create surface volume (I animate the scale to zero so stops emiting), I saw on the first frame all the particles, but on the next frame all points and attributes disapears except one. Why?

-Atributte transfer: This atribute is really cool, but some questions: you can adquire atribute value based on distance, but if you want to conserve the atribute? Imagine I have Atribute1 in a plane with value 0 for all the points. I have atribute 1 with value 5 in a ball that move along this surface, I want to transfer the atribute1 value from ball to point plane, but when the ball move along the surface the atributes restart to zero. I know already the trick of use a "trail" to the ball, but in other cases this will not work (imagine transfer a viscosity atribute from one object to a fluid sim) there is no other way?.

--Atributte transfer again: There is a way to transfer a value based also on time an acumulative? The same example before, but I want to increase the atributte based on distance to the sphere and over time, so if the sphere stops, the near points of the plane will be increasing, but when the ball go away the attribute will not increase more the value.

-Another question not related with atributes: I tryed to import a fbx animation but doesn't work, its because I'm on aprentice version? I tryed also with alembic and I fault. Finally I can do it exporting obj sequences from max, but the viewport performance was very bad (a simple box moving and moving on the timeline was like 1fps.

Thanks for any help on any point, this is a great forum, hope I can contribute soon.

[anim]

I would say do a little search on forums since some questions like accumulating attributes repeat unnecessarily too often

1. I assume you are talking about POPs, then just fill in the Birth Group name on Source POP and keep Preserve Group off, so every particle that has just been born will be in that group, but on the next timestep it will be removed from it

then just run your Attribute POP for that group, so it sets your attribute to be $TY only when the particle is born then it will keep the value

2. are you in simulation context? POPs, DOPs or Solver SOP? it seems like you are in standard SOPs so there is no geometry passing from previous frame and therefore the particles are generated from geometry on current frame. Big emitter -> lots of particles, Emitter scaled to 0 -> maybe one particle

3. again simulation environment is the answer for that, Solver SOP, SOP Solver DOP or POPs, do your attribute transfer in there, it will keep the previous values

4. the same, maybe instead of pure attribute transfer you can use VOP SOP with pointclouds to add values by distance instead of overwrite

but even with only attribute transfer you can do branch of your geo where you zero that attribute, transfer current frame contribution from the sphere, then use simple VOP SOP to add those values to geo coming from previous frame

5. I'm not sure but I think import in apprentice should work, just FBX and Alembic export is limited

obj sequence should be very fast for simple box

[ryew]

I would definitely suggest looking at some of Peter Quint's brilliant free tutorials - https://sites.google...oudinitutorial/ .

He has tutorials for using both Attrbute Transfer, Solver and ForEach SOPs that will likely answer most of your questions and give you a good idea of how to expand upon those.

https://sites.google.com/site/pqhoudinitutorial/home/videos-on-the-basics-1 - Attributes and For Each SOP

https://sites.google.com/site/pqhoudinitutorial/home/videos-on-sops - Attribute Transfer SOP

https://sites.google.com/site/pqhoudinitutorial/home/videos-on-dynamics - SOP Solver

Edited May 17, 2013 by ryew