[Sidefx-houdini-list] basic instancing question

Olex P hoknamahn at gmail.com
Mon Oct 27 12:13:45 EDT 2008


Check this out Jon http://omlc.ogi.edu/pubs/prahl-pubs/prahl88/node10.html

On Mon, Oct 27, 2008 at 4:06 PM, jon parker <parker.jon at gmail.com> wrote:

> Hi Olex,
> I'm probably not versed enough to understand what you mean by
> anisotropic scattering with phase functions... is it possible to
> explain that a bit more clearly?
> -Jon
>
> On Sun, Oct 26, 2008 at 2:06 PM, Olex P <hoknamahn at gmail.com> wrote:
> > Yes you can. Point is completely tha same primitive as polygon with only
> > one... two exceptions:
> > 1. Shader executed once on point (i.e. it's impossible to get spherical
> like
> > shading on the single point)
> > 2. You can't (I dunno why because it still make sense) displace point. As
> > workaround you can displace them in SOPs.
> > The rest is the same.
> >
> > On Sun, Oct 26, 2008 at 4:56 PM, Pablo Giménez <pablogipi at gmail.com>
> wrote:
> >
> >> 2008/10/26 Olex P <hoknamahn at gmail.com>
> >>
> >> > You could render them as Mantra points (using phase functions for
> >> > anisotropic scattering if you need it).
> >> > This could give you:
> >> > 1. Simpler setup
> >> > 2. Good details
> >> > 3. Super fast rendering
> >>
> >> Hey Olex when you render as Mantra points, can you apply a shader to
> them?
> >> Or the points only use the Cf and Of point attributes, I remember to
> have
> >> had some problems applying shaders to points in the pst, not sure now
> ...
> >>
> >> >
> >> >
> >> > On Sat, Oct 25, 2008 at 8:55 PM, jon parker <parker.jon at gmail.com>
> >> wrote:
> >> >
> >> > > Thanks for the repsonse...
> >> > > A colleague also tipped me to using displacement mapping to add
> detail
> >> > > to volumes, and it works really well.  For general volumetric
> >> > > rendering I'm in agreement with all of the things below.  With what
> I
> >> > > have been tasked with, there is a large scale difference in the
> nebula
> >> > > as a whole, versus the details we're trying to show... there are a
> >> > > large number of tiny 'knots' in the nebula that need to be in the
> >> > > right place according to some astronomical observation data I've
> been
> >> > > given.  My first attempt was to birth metaballs from the right
> >> > > locations and render them volumetrically, embedded within the rest
> of
> >> > > the gas volume.  But the shading quality of metaballs doesn't seem
> to
> >> > > be as nice as I hoped.  In fact I ran a test where I converted them
> to
> >> > > a massive image3d texture, and the shading quality was much nicer,
> but
> >> > > generating it took forever and that really hinders that technique
> for
> >> > > testing.  So my latest idea is to use a lot of knot-shaped volume
> >> > > instances, and displace them in world space to add variety, but they
> >> > > seem to be displaced before they are instanced, and not afterwards
> >> > > like I hoped.  Any other suggestions towards creating them this way?
> >> > > --jon
> >> > >
> >> > > On Sat, Oct 25, 2008 at 9:01 AM, Pablo Giménez <pablogipi at gmail.com
> >
> >> > > wrote:
> >> > > > Sounds pretty good.
> >> > > > The dispalcement to do the convection is quite interesting
> >> > > >
> >> > > > 2008/10/24 Remba, David (Space Technology) <David.Remba at ngc.com>
> >> > > >
> >> > > >>
> >> > > >> I've been working on clouds, and had good results
> >> > > >> using simple geometry (spheres, boxed shapes) then
> >> > > >> subdividing to round the shapes, then iso-offset to
> >> > > >> create a low density volume (20x20x20).
> >> > > >>
> >> > > >> The good stuff happens in a custom material:
> >> > > >>
> >> > > >> 1. displacement VOP SHOP uses various noise functions
> >> > > >> to push P around (for clouds: only in the up +Y direction
> >> > > >> to simulate convection, and using an abs() to make it
> >> > > >> puffy looking).  For nebula I would try the built-in
> >> > > >> aanoise VOP.
> >> > > >>
> >> > > >> 2. surface VOP SHOP based from the VEX Volumecloud shader,
> >> > > >> and added extra features for clouds to cut off and
> >> > > >> darken the bottom.  Higher density makes the gas more
> >> > > >> chunky looking, lower values make it more wispy looking
> >> > > >> (good for nebulas).
> >> > > >>
> >> > > >> tips:
> >> > > >>
> >> > > >> Very important to adjust the Volume Step size to as large
> >> > > >> a value as possible (just below the noticeable speckle artifact).
> >> > > >>
> >> > > >> For fast rendering: try only one or two lights; if you need
> >> > > >> more, do multiple render passes and comp them.  Use Ray Trace
> >> > > >> Engine, lower opacity limit to 0.9 if the nebula/clouds are
> >> > > >> chunky.
> >> > > >>
> >> > > >> For nebula you might try some glow effects (see the emit
> >> > > >> in the VEX Super Material shader).
> >> > > >>
> >> > > >> p.s. For nebulas, you might try separating very far objects
> >> > > >> which are more of a 2D problem, from closer 3D objects.
> >> > > >>
> >> > > >> p.p.s. I work at a space technology company so I might get
> >> > > >> to work on nebulas soon also!  I'd like to hear you things
> >> > > >> go for you.  My email:  daveremba at yahoo.com
> >> > > >>
> >> > > >> I hope this helps,
> >> > > >>
> >> > > >> Dave
> >> > > >>
> >> > > >> _______________________________________
> >> > > >> David Remba
> >> > > >> Tel 310 813 5899 Cel 310 809 6375
> >> > > >> Northrop Grumman Space Technology
> >> > > >> IMAGE Center
> >> > > >>
> >> > > >>
> >> > > >>
> >> > > >> -----Original Message-----
> >> > > >> From: sidefx-houdini-list-bounces at sidefx.com on behalf of jon
> >> parker
> >> > > >> Sent: Wed 10/22/2008 9:13 PM
> >> > > >> To: sidefx-houdini-list at sidefx.com
> >> > > >> Subject: [Sidefx-houdini-list] basic instancing question
> >> > > >>
> >> > > >> Greetings esteemed Houdini masters!
> >> > > >> I've been tasked to create a planetary nebula by some very
> demanding
> >> > > >> scientists... I've done some lighting for studios using Houdini
> in
> >> the
> >> > > >> past, but now the holes in my knowledge about Houdini are showing
> >> up,
> >> > > >> so I am looking for some basic workflow questions to be cleared
> up.
> >> > > >> For the nebula, the basic gas volume is looking great, however
> there
> >> > > >> are a large number of 'knots' in the nebula that need to be quite
> >> > > >> detailed.  I tried using volumetric metaballs first, but these
> don't
> >> > > >> seem to shade as nicely as the volume primitives... the density
> >> > > >> gradients don't seem as smooth, and the edge glows just aren't
> there
> >> > > >> like they are with volumes.  Converting them to i3d files gave me
> a
> >> > > >> much better look, but that's quite time consuming during look
> >> > > >> development, since I need at least 1024^3 i3d files to maintain
> the
> >> > > >> detail.  So I've tried instancing volumes to each knot, and this
> >> > > >> potentially looks best, except I have two questions about it...
> >> > > >> firstly, what is the best way to transfer point attributes to the
> >> > > >> volume?  Secondly, how can I use world space displacement on an
> >> > > >> instance?  On the first attempt I discovered that instances
> >> themselves
> >> > > >> are not displaced; instead they pick up the displacement of the
> >> source
> >> > > >> geo before they are instanced.   Aside from this question, which
> >> > > >> approach makes the most sense?  There are obviously a lot of
> >> potential
> >> > > >> paths to take in Houdini.
> >> > > >> Cheers,
> >> > > >> Jon
> >> > > >> _______________________________________________
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> >> > > >>
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> >> > > >>
> >> > > >>
> >> > > >> _______________________________________________
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> >> > > >>
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> >> > > >>
> >> > > >>
> >> > > >
> >> > > >
> >> > > > --
> >> > > > Un saludo
> >> > > > Best Regards
> >> > > > Pablo Giménez
> >> > > > _______________________________________________
> >> > > > Sidefx-houdini-list mailing list
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> >> > > > https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
> >> > > >
> >> > > _______________________________________________
> >> > > Sidefx-houdini-list mailing list
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> >> > >
> >> > _______________________________________________
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> >> >
> >>
> >>
> >>
> >> --
> >> Un saludo
> >> Best Regards
> >> Pablo Giménez
> >> _______________________________________________
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> >> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
> >>
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