[Sidefx-houdini-list] basic instancing question

Pablo Giménez pablogipi at gmail.com
Sat Oct 25 09:01:17 EDT 2008


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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-- 
Un saludo
Best Regards
Pablo Giménez



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