Monday, April 20, 2009

Emiter update.

TroY manged to find a bug or two with emitters. So setting normals should work now. Don't forget that for the object to be animated you must uncheck the static checkbox. Also Emitters are still "old" code in that only vertex's emit fluid and their normals are defined by the AoI object, so you need shading to be set for the object. Same link as always.


TroY said...

Ahh, yap. That did the trick. :) Thanks!

(To be honest, I indeed forgot to activate shading... However, it didn't work with a SplineMesh either which is set to "Approximating" by default. Phew.)


bob said...

You need to convert to triangle mesh and then set to shading for emitter. It will be better when thats all tris too. But for now thats what you need to do.

TroY said...

Alright, thanks. :)

I'm currently about to write a german tutorial/documentation. Most people start to play with the plugin and they'd really like to understand it, but there's very few german doc available (and my own guide is outdated) -- so they give up quite soon. My goal is to explain all regular options in detail and maybe some of the options in the "advanced" dialog. But there are some things that I don't really understand yet, mostly about boundaries:

- What exactly does "calculate boundary outside poly" do? As far as I understood, you first check whether the intersection point of a particle with the plane of a polygon lies within that polygon or not. If not (and if that option is disabled), nothing happens. But what happens if that option is enabled? (Is my approach more or less correct? Or does your intersection test work completely different?)

- I'm not that deep into friction yet, but what exactly is the meaning of "boundary friction"? Is it the ยต in Coulomb friction? I'd be happy to tell people: "Set this to 0.6 and you'll get about 'Aluminum on Steel'", well, some kind of reference values.

- Not that I'd need that feature, but does disabling "is poly boundary" still have any effect? I'd expect the old vertex-based behaviour to become active but poly boundaries are used in any case.

- Soft Bodies: Is "Boundary force" used in any way yet? If so, what does it mean?

Big thanks in advance for any help!

We're planning to translate that doc when it's about to be done. So maybe it could serve as some kind of a base for an "official documentation" -- or whatever. ;)


bob said...

Awesome that you doing some docs.. I really should do some...

Q) calculate boundary outside poly..

First a normal line from the plane of the ploy is projected up to the particle and its distance is checked. If it further than some distance then we move to the next particle.

If its less than some distance we check were the projected line intersects the triangle. If the point is outside the poly and we don't do outside polys.. then we ignore it. Otherwise we calculate the distance to the closest point on the edge of the triangle and use that distance.

So in a nutshell, without outside calculation a boundary can only effect particles that lie in the volume of the poly swept through its normal vector.

The reason for this is that if we do calculated outside polys -- we can get odd results with concave boundary

Q) Friction.

Friction is not really physically meaningful. But it often is not in a lot of simulation codes. It is just a drag coefficient --BUT particle size strongly affects the results.

The accurate way with the current system would be to force a no slip condition. But again unless your particles are small enough to capture the boundary layer effects, its not so physically meaningful.

However for a lot of interesting cases this is probably good enough.

Q) Does disabling is Poly have an effect?

I don't think it does... But i havnt checked.

Q) Soft bodies...

Yes, but with the new solver it may not make a huge difference anymore. Remember that softbodys interact with vertices's onto polys -- not poly to poly...This force was to help prevent penetration.

TroY said...


thank you for those explanations! That was a great help. :)


Anonymous said...

Just wanted to say, that this plugin really looks promising.
How are your plans for integration with Blender, or are you concentrating on AoI only?

bob said...

I am focusing on AoI at the moment...

Well from the frequency of updates, I would focusing is not the right word.

Blender has a pretty good fluid sim anyway

afifi said...

bob, where can i find any documentation or tutorial regarding your physics plugins.. really interesting and fyi, related to my work also.. fluid dynamics (more specific gas dynamic)..