Re: shading geometry instanced to particles

[benp <benp(at)rsp.com.au>]

yeah, brillo. I actually had this in mind to try :P (honestly!).
it's just that i've got other <really interesting> per-particle vars 
that i'd love to render.
But that's a great suggestion, thanks Andy.

Andy Jones wrote:
> I don't think this solves the general case of moving particles, but a 
> trick I've used for customizing instances in the past is to take a 
> fixed vector (say, [0,0,0]) and feed it through a vector coordinate 
> converter node set to  "point, to object" (thereby obtaining a unique 
> vector per object, assuming all the different objects have different 
> transforms), then feed the result into a fractal.  This gives you a 
> way to customize objects per-instance in a way that doesn't 
> necessarily "appear" to vary positionally (with a high res fractal).  
> The color_interpolate node (available only by browsing through the 
> shader presets) is handy in situations like this, since it can work 
> like a multi-threshold switch, allowing you to use smoothly 
> interpolating colors to switch between a handful of different textures.
>
> - Andy
>
> benp wrote:
>
> > thanks for the answer halfy, makes sense.
> > out of curiosity, has this been a popular problem at all?
> >
> > i guess i'll have to use my freakn brain to get around this one for 
> > the moment :P
> > benpee
> >
> > Halfdan Ingvarsson wrote:
> >
> > > Currently it's not possible.
> > >  
> > > There's a missing feature in mental ray that would've made this easy 
> > > to support, which would've involved attaching particle userdata on 
> > > each instance. In current versions of mental ray, when attaching 
> > > userdata to an instance, it modifies any existing userdata on the 
> > > same instance which fails miserably when trying to apply that 
> > > userdata on a instanced hierarchy (delete becomes extremely hairy). 
> > > This is because userdata is defined as a linked list, where the tag 
> > > id of the next userdata is stored in the userdata header itself, 
> > > rather than a flat list with indirection (as is done for shader 
> > > lists). We're working with mental images to address this.
> > >  
> > >  - ½
> > >
> > > ------------------------------------------------------------------------ 
> > >
> > > *From:* owner-xsi(at)Softimage.COM on behalf of benp
> > > *Sent:* Tue 02-Jan-07 20:58
> > > *To:* XSI(at)Softimage.COM
> > > *Subject:* shading geometry instanced to particles
> > >
> > > hi list,
> > >
> > > I'm using geometry instanced to particles (using the Instancing 
> > > stuff in
> > > the PType).
> > > But i was wondering if anyone had any experience with using particle
> > > data in the rendertree for the instance masters. Please note that  i'm
> > > not talking about the rendertree for particle types here, just the
> > > rendertree on the geometry i'm instancing to the particles.
> > >
> > > scenario:
> > > Say you had a geo of a nice little 4-leafed clover. Then you want to
> > > instance it over a landscape using particle instancing.
> > > The clover will only be shaded by the one shadetree, unless you have
> > > more clovers in the instancing group each with unique shaders. This 
> > > gets
> > > limiting as you'd have to have as many geo-masters and shaders as there
> > > are varieties of clovers.
> > > What I'd prefer to do is have one geo master, and one master shader 
> > > that
> > > can pull out particle data (that i've written to the particle cloud)
> > > from the instances to shade the clovers uniquely.
> > >
> > > I don't know if this is currently limited by XSI needing a shader
> > > written, or XSI not yet exporting the particle data to particle 
> > > instances.
> > > Does anyone have any advice??
> > >
> > > And yes, i have tried the Particle_Color (et al)  nodes on instance
> > > masters: No luck!
> > > But I do get a warning from mr : "#INFO : PHEN 0.2 warn : Bad particle
> > > raystate (00000000)" ...
> > >
> > > tia,
> > > benpee
> > >
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