[Sidefx-houdini-list] basic instancing question

Olex P hoknamahn at gmail.com
Wed Oct 29 06:19:02 EDT 2008


If you really need it you could calculate N as function of distance between
current shading sample and center of circle or grid/sprite. But "spherical
shading" probably isn't a good term for this effect.

On Tue, Oct 28, 2008 at 11:24 PM, jon parker <parker.jon at gmail.com> wrote:

> 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
> >> >
> >> _______________________________________________
> >> 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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