[Sidefx-houdini-list] basic instancing question

jon parker parker.jon at gmail.com
Mon Oct 27 12:06:14 EDT 2008


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