[Sidefx-houdini-list] basic instancing question

jon parker parker.jon at gmail.com
Tue Oct 28 19:24:53 EDT 2008


Maybe you could create a spherical normals texture and use that for
the N variable?

On Tue, Oct 28, 2008 at 6:11 PM, Pablo Giménez <pablogipi at gmail.com> wrote:
> mmmm and how I can implement spherical shading in Mantra?
>
> 2008/10/28 Olex P <hoknamahn at gmail.com>
>
>> Yep, any interpolation which could make a flat object (grid, circle) look
>> 3d. Which is impossible for point even if that point has a huge scale and
>> covers the whole screen.
>>
>> On Mon, Oct 27, 2008 at 11:36 PM, Pablo Giménez <pablogipi at gmail.com>
>> wrote:
>>
>> > thanks for the response Olex, also what is spherical shading? is like
>> > spherical interpolation of shaded points?
>> >
>> > 2008/10/27 Olex P <hoknamahn at gmail.com>
>> >
>> > > 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
>> > > > >> > > >> _______________________________________________
>> > > > >> > > >> Sidefx-houdini-list mailing list
>> > > > >> > > >> Sidefx-houdini-list at sidefx.com
>> > > > >> > > >>
>> > > > https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>> > > > >> > > >>
>> > > > >> > > >>
>> > > > >> > > >> _______________________________________________
>> > > > >> > > >> Sidefx-houdini-list mailing list
>> > > > >> > > >> Sidefx-houdini-list at sidefx.com
>> > > > >> > > >>
>> > > > https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>> > > > >> > > >>
>> > > > >> > > >>
>> > > > >> > > >
>> > > > >> > > >
>> > > > >> > > > --
>> > > > >> > > > 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
>> > > > >> > > >
>> > > > >> > > _______________________________________________
>> > > > >> > > Sidefx-houdini-list mailing list
>> > > > >> > > Sidefx-houdini-list at sidefx.com
>> > > > >> > >
>> > https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>> > > > >> > >
>> > > > >> > _______________________________________________
>> > > > >> > Sidefx-houdini-list mailing list
>> > > > >> > Sidefx-houdini-list at sidefx.com
>> > > > >> >
>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>> > > > >> >
>> > > > >>
>> > > > >>
>> > > > >>
>> > > > >> --
>> > > > >> 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
>> > > > >>
>> > > > > _______________________________________________
>> > > > > Sidefx-houdini-list mailing list
>> > > > > Sidefx-houdini-list at sidefx.com
>> > > > > https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>> > > > >
>> > > > _______________________________________________
>> > > > Sidefx-houdini-list mailing list
>> > > > Sidefx-houdini-list at sidefx.com
>> > > > https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>> > > >
>> > > _______________________________________________
>> > > Sidefx-houdini-list mailing list
>> > > Sidefx-houdini-list at sidefx.com
>> > > https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>> > >
>> >
>> >
>> >
>> > --
>> > 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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>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>
>
>
>
> --
> 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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