Re: One big texture on many small instances?

["peter boeykens" <peter_b(at)skynet.be>]

sorry all for the attachment.


mapped image across instances...
all necessary info to recreate this should be visible in the screendump

its even simpler than I said previously, no need for gradient nodes.
(allthough you could use them to warp the image - could be cool)







----- Original Message ----- 
From: "Pingo van der Brinkloev" <pingo(at)pingofilm.dk>
To: <XSI(at)Softimage.COM>
Sent: Thursday, August 02, 2007 11:19 PM
Subject: Re: One big texture on many small instances?


Hey Peter.
This sounds really interesting, and a bit advanced - at least to me. Is 
there
anyway you could give some more info on this technique? I tried recreating 
it,
but there are to may things that are not aparent to me...

would it be possible with eg. a screendump of a setup?

hope it's not to much trouble.

cheers

pingo

peter boeykens (peter_b(at)skynet.be) wrote:
> > You're right, rendering is as long, but scene interaction is much faster
> > using instances. Plus, if the model changes they're much easier to
> > update...
> >
> > I'll probably use duplicates, however I'm still wondering why texture 
> > UV's
> > are evaluated only once when everything else is evaluated for each
> > instance... Oh well...
>
> thats not really true.
> apart from the transforms almost nothing is evaluated "per instance".
> true enough, textures that are spatial will be evaluated properly, but 
> thats
> not per instance, but rather per sample - the texture itself is one and 
> the
> same for all instances, it just looks different at different points in
> space.
>
> if you use an image implicit and feed that proper coordinates it should 
> also
> stretch through all the instances.
> something like making a floor with tiles and having one big painting on
> them?
> It would be fixed in space though, and if your instances move they would
> "swim" through the texture.
>
> Making the coordinates for this is not so trivial though.
> If I remember correctly, you need a vector state set to intersection 
> point,
> then plug that into 2 B/W gradients that use the vector x and the vector z
> respectively. you can do the placement through the min and max. those
> gradients converted to scalars could be fed into a vector again that would
> in turn feed the image implicit.
>
> A lot of hassle to get it to work and quite limited, since you'd be
> restricted to either xy, xz or yz plane.
>
>
>
>
>
> > Thanks for the reply.
> >
> > Antonin
> >
> > Bernard Lebel wrote:
> >> Any particular reason why you're using instances? The only situation
> >> where I think instances are useful is for static, unchanging objects.
> >> Even then, I now resort more on particle instances than instances.
> >> They take long to save, and they have to be populated when you open
> >> the scene.
> >>
> >> It is my understanding that render-wise, instances won't save you
> >> anything as well. Real geometry would allow you to do what you want.
> >>
> >>
> >> Bernard
> >>
> >>
> >>
> >>
> >> On 8/2/07, Antonin Messier-Turcotte <amessier(at)flystudio.com> wrote:
> >>
> >>> Thanks for the reply... I'm not sure if it would work in my case 
> >>> though.
> >>> Seems like the switcher has only 16 inputs, where I've got about 500
> >>> instances. Plus, my texture doesn't repeat, it's one big texture
> >>> covering the entire instance formation. So I don't think it would 
> >>> work,
> >>> or maybe I'm misunderstanding your idea...?
> >>>
> >>> What's weird is that all shaders (for example phong or lambert, or
> >>> reflection or even dirtmap) will be evaluated for each instance, while
> >>> texture maps are only evaluated for the master model. Why is that?
> >>>
> >>> Antonin
> >>>
> >>> Sam Cuttriss wrote:
> >>>
> >>>> probably not instances,
> >>>> but i imagine with the ba colourswitcher shader set to random you
> >>>> ought to be able to offest the image uv remap parameters.
> >>>>
> >>>> just make your uvs the size of one repeat (on your image) then offset
> >>>> by integers and you should be able to do it cleanly.
> >>>>
> >>>> there may be a cleaner way?
> >>>> _sam
> >>>>
> >>>> *Sam Cuttriss
> >>>> * Janimation 3D Aficionado
> >>>>
> >>>>
> >>>> Antonin Messier-Turcotte wrote:
> >>>>
> >>>>> Hi,
> >>>>>
> >>>>> Let's say I've got a big object made up of little cubes. Is there 
> >>>>> any
> >>>>> way the cubes can be instances, yet they would grab a different part
> >>>>> of a big texture that is projected on the whole big object? I can't
> >>>>> seem to find a way to do this, even if the texture support is 
> >>>>> outside
> >>>>> the model that was instanced. Shouldn't it be possible?
> >>>>>
> >>>>> Thanks!
> >>>>>
> >>>>> Antonin
> >>>>>
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Attachment: rtree_instances.jpg
Description: JPEG image