Re: A couple of RBD questions

["Morten Bartholdy" <xsi(at)colorshopvfx.dk>]

Thanks a lot André - this is cool :)

- MB



----- Original Message ----- 
From: "André Adam" <a_adam(at)49games.de>
To: <XSI(at)Softimage.COM>
Sent: Thursday, June 28, 2007 11:26 AM
Subject: Re: A couple of RBD questions


There you go. This is JScript. Just select a bunch of objects and you
get a particle cloud which you can drive with any forces. Currently the
script only transfers the objects' positions to the particles, not their
rotations (yep, I have been lazy). In other words, if your objects have
rotation applied, the particles will reset them to 0/0/0, so do a freeze
rotation beforehand if this applies to your scene.
If you want to combine this with RBDs, you can make the objects passive
RBDs and simply switch them to active at any time you like, the RBD
engine will instantly take over and make the objects leave their
particle trails.

Hope that helps, cheers!

   -André


Morten Bartholdy wrote:
> It sounds good André - I also need to do a load of smaller pieces of
> concrete and was just looking into ways to do that on top of my large
> piece simulation. I would be hvery grateful if you would pass me that
> script. Thanks a lot!
>
> Cheers
> Morten Bartholdy
> 3D & VFX Artist
>
>
>
>
>
> ----- Original Message ----- From: "André Adam" <a_adam(at)49games.de>
> To: <XSI(at)Softimage.COM>
> Sent: Wednesday, June 27, 2007 5:59 PM
> Subject: Re: A couple of RBD questions
>
>
> > I've just done something like this using a combination of scripting,
> > particles and RBDs. Basically I sketched a particle cloud, one
> > particle for each object, created a particle cloud with simulation
> > props from the sketched cloud, then created a cluster constraint from
> > each object to its corresponding particle and finally used this setup
> > to shoot the rocks out of the wall using the particle system. As soon
> > as the rocks did not sit on top of each other anymore I switched the
> > rocks' RBD properties from passive to active and let the RBD engine
> > do the floor collisions. Worked out nicely, with a script creating
> > the particle setup from the selected rocks in one go.
> >
> > If this workflow would be of help for you I could provide you with
> > the script to do the setup.
> >
> > Cheers!
> >
> >    -André
> >
> >
> > Morten Bartholdy wrote:
> > > I am breaking a wall with RBD and am using a set of pieces which are
> > > slightly smaller then the ones I want to render so I can avoid
> > > interpenetration in the beginnnig of the simulation. Now I know I
> > > can transfer the cache to a clip in the mixer, but if I want to copy
> > > this motion to each renderpiece or constrain these to the RBD'ed
> > > pieces it starts looking a bit complicated. If I create a cluster
> > > with center my RBD is shot. Next thing I would try is to multi point
> > > constrain my renderpiece to the RBD piece but this requires me to
> > > create three clusters on each RBD piece and then three point
> > > constrain each renderpiece to those. Please tell me Softimage
> > > thought of easier ways to handle something like this with up towards
> > > 100 separate RBD pieces???
> > >  Another thing is my pieces tend to explode a bit away from each
> > > other even though I have made absolutely sure there are no
> > > interpenetrations at the bewginning of the sim. I have increased
> > > simulation and collision acuracy to very high levels without quite
> > > getting rid of this behaviour. Also I have elasticity all the way
> > > down to 0.001 since these are supposed to look like concrete pieces,
> > > but I still get weird styrofoam like bounce and sploinng-like fly
> > > away behaviour from the odd piece when it collides with something
> > > again after landing on the ground. I have tried messing with
> > > friction parameters without much luck.
> > >  I am guessing there a tips and tricks I still need to learn about
> > > the wonderful world of RBD'ing so if someone knows a way to dampen
> > > simulation collisions I would be happy to hear them, if someone in
> > > the know cares to share some insight.
> > >  Thanks!
> > >  Morten Bartholdy
> > > 3D & VFX Artist



--------------------------------------------------------------------------------


/*========================================================
 "Selection To Particles" / André Adam
 Constrains a selection of objects to a newly created particle cloud.
 Resets the objects rotation in the current implementation!
========================================================*/


//Create a particle type for later use
var oPTypeRtn = CreateParticleType(siBillboardType);
var oPType = oPTypeRtn.Value("Output");

//Create an empty particle cloud and get its primitive
var oCloud = ActiveSceneRoot.AddParticleCloud(oPType, "Sketched Particles");
var oPrimitive = oCloud.ActivePrimitive;

//Copy the selection into a new collection to avoid trouble with selection 
changes
var cSel = Selection;
var cCopySel = new ActiveXObject("XSI.Collection");
cCopySel.AddItems(cSel);

//Create an empty array and fill it with position data from selected objects
var aPos = new Array();
for(var i=0; i<cCopySel.Count; i++){
 aPos.push(cCopySel(i).Kinematics.Global.Transform.PosX);
 aPos.push(cCopySel(i).Kinematics.Global.Transform.PosY);
 aPos.push(cCopySel(i).Kinematics.Global.Transform.PosZ);
}

//Create particles in the cloud
oPrimitive.AddParticles(cCopySel.Count, oPType);
//Position particles in the cloud
oPrimitive.Particles.PositionArray = aPos;

//Create a new cloud using the old one as an initial state; the new cloud 
owns simulation properties
var oInitialStateCloud = CreateParticleCloud(oCloud)(0);
oInitialStateCloud.Name = "Simulation Particles";

//Make particles live forever
oCloud.Properties("Initial State Property").Parameters("liveforever").Value 
= true;

//Create clusters from the new cloud's particles and constrain the former 
selected objects to them
var oGeo = oInitialStateCloud.ActivePrimitive.Geometry;
for(i=0; i<cCopySel.Count; i++){

 //Create cluster
 var oCluster = oGeo.AddCluster(siVertexCluster, cCopySel(i).Name, (i));

 //Create constraint and set tangent and upvectors
 var oConstraint = cCopySel(i).Kinematics.AddConstraint("ObjectToCluster", 
oCluster);
 oConstraint.Parameters("tangent").Value = true;
 oConstraint.Parameters("dirx").Value = 0;
 oConstraint.Parameters("diry").Value = 0;
 oConstraint.Parameters("dirz").Value = 1;

 oConstraint.Parameters("upvct_active").Value = true;
 oConstraint.Parameters("upx").Value = 1;
 oConstraint.Parameters("upy").Value = 0;
 oConstraint.Parameters("upz").Value = 0;
} 


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