[Sidefx-houdini-list] Get life attribute with fluid

Sebastian H. Schmidt sebastian.h.schmidt at googlemail.com
Thu Oct 8 17:55:46 EDT 2009


hey francois


one thing i've forgot i dont know if you realised it,
make sure that the scalar field that you've created in 1, has the same
dimensions/resolution & position as your fluid field

about the gas calculate node:
you can do some basic maths on a certain field with it so
increasing/decreasing values through pre/post adds or multiplies (thats d)
and of course do some maths with other fields as well (thats c)

so my idea behind it was,
.... for each timestep increment all current field values by the timestep
(or e.g. 1) that is the aging process
... and than to add the "new-born"-fluid to it use the calculation method
minimum:
     what that thing does,  ... for each "voxel-cell" in both fields it
takes the one with the smallest ammount and puts it into the "myLife" pass.
    that can lead to problems if it takes the zero-density voxels which are
not emitting any water, and therefore the life in that cells will always be
set to zero


Seb

On Thu, Oct 8, 2009 at 10:37 PM, Francois Duchesneau <sidefx at trinix.ca>wrote:

> Thanks for the answer Sebastian,
>
> I think I've almost set it up except for point c and d. I will try to
> understand better how the Gas Calculate work because it doesn't seem to
> work and I can't figure out the logic you told me.
>
> Here are the parameters I've set for the Gas Calculate
> Dest Field=myLife
> Source Field=source
> Calculation=Add
> Dest-pre add=$TIMESTEP
>
>
> François
>
> > hey francois,
> >
> > here how i would do it, ... just freestyling i have no H at my disposal
> at
> > the moment
> >
> > 1) create a new scalar field & name it "myLife" and maybe set its initial
> > value to something increadibly high
> > 1.b) you can use a scalar-field vizualization node piped into this scalar
> > field to visualize the field!
> > 2) apply this to your fluid field using the apply-data dop
> >
> > 3) on your fluid solver create a gas calculate node
> >    a) which adds the contents of the source field "source"
> >    b) into the destination field "myLife"
> >    c) the calculation method you want to use could be "min", so all the
> > fluid that is added comes in with a life value of something like 1
> >    d) what you also can do is setting the dest-(pre or post) add to your
> > timestep so destiny field "myLife" gets incremented each calculation step
> >    one thing on c) i'm not sure what happens if your source field
> contains
> > any  fields with zero as content, if that sets all the myLife to zero
> > though
> > ?? worth trying, maybe some kind of mask or something is arround that you
> > can missuse ;)
> > 4) use an gas-advect node to advect the "myLife" Field using the "vel" -
> > Velocity Field
> >
> > give it a try
> >
> > Seb
> >
> >
> >
> > On Thu, Oct 8, 2009 at 8:53 PM, Francois Duchesneau
> > <sidefx at trinix.ca>wrote:
> >
> >> Hi everybody,
> >>
> >> I'm trying to get the life of a voxel fluid simulation in order to fade
> >> off the opacity at some point like I would do with particles. How can I
> >> do
> >> that?
> >>
> >> Thanks for your ideas.
> >>
> >> François
> >>
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