[Sidefx-houdini-list] basic instancing question

Pablo Giménez pablogipi at gmail.com
Sun Oct 26 12:56:03 EDT 2008


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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> > >> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
> > >>
> > >>
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> > >>
> > >>
> > >
> > >
> > > --
> > > Un saludo
> > > Best Regards
> > > Pablo Giménez
> > > _______________________________________________
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-- 
Un saludo
Best Regards
Pablo Giménez



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