It's not technically an instance limitation - it's an XSI limitation -
mental ray has the shader seperate for the geometry for instances - so
you could actually have a completely different shader on every
instance, but XSI doesn't provide support for this functionality.
If you write a geometry shader that takes the particle userdata blob
and an object you could do it. You've even got a few choices from
there - one of them is to find some funky way to build new materials
for each one. Alternatively you could attach a userdata blob to each
instance when you created it - have a colour in that userdata blob,
then write a shader which looks up the userdatablob of the instance
it's rendering and output that color. This way you could just copy the
one material across all the instances.
The second way would probably be easier to implement.
Cheers,
Alan.
On 8/8/06, peter boeykens <peter_b(at)skynet.be> wrote:
Its not a particle limitation, its an instance limitation really.
Allthough its mostly with particle instancing that it comes up.
Instances inherit their shader from the master object, and there's nothing
you can do about that, except write your own shader...
There is a case where you can workaround it, and that is when using
instances for set dressing.
(eg rocks or pebbles, or strands of grass or ...)
You can use procedurals, with world coordinates, perhaps plugged into a
gradient, to create random colors.
But it would be a fixed pattern in worldspace, and if your instances are
animated they would "swim" through that pattern. Hence the "set dressing"
requirement.
Alternatively, I often create a handfull of master objects layed out in a
grid and texture them with some variation through the shader, to make them
all look unique. Its still not random colors per particle of course, but
it'll help a lot in breaking up the uniformity.
And in this scenario you can freeze the textureprojection and they will
behave when animated, so you're not limited to set dressing.
> Here is a little task for all of you particle savy people out there.
>
> 1.) Create a particle system with instances (1 object will do for now)
> 2.) Make them have random colors
> 3.) Tell me how you did
>
> I wish there would be a control for PerParticle or a shader color
> override for instances. I would like to have random colors on "Per
> Instance" object...
>
> Anyone knows if this is possible at all?
>
> regards
> stefan
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