Coloring Instancer Geometry On Per Particle Basis

[amitc]

Hello,

I have somewhat perplexing question.
My search in the documentation makes me think that this may not be possible, but folks her may have a solution

Lets say we have a particle system with a bunch of particles
Now lets add a per particle color attribute rgbPP to our particle system
We can go and assign colors to each particle through the component editor.

Now lets create a cylinder
Then do particle>instancer replacement
this gives us cylinders at each particle location.

Now we want to color these cylnders using the rgbPP or per particle color attribute.

Any clues how this can be accomplished.

Help appreciated.

Thanks
--Amit

[joojaa]

Its not elementary possible. But if your not afraid of writing a sahder yourself then it is possible the naming of instancer units is predictable and a MR shader can go and pick the thing up form a array*. Also its possible in renderman for maya, and renderman studio pro by default.

Or you can just use many many copies.

*i think i have a early proof of concept (its hard to use but it does work) somewhere lying around you can get it if i find it.... Damnd its on my old computer. Doh

[amitc]

QUOTE(Joojaa @ 07/11/09, 05:46 AM) [snapback]311312[/snapback]
But if your not afraid of writing a sahder yourself then it is possible the naming of instancer units is predictable and a MR shader can go and pick the thing up form a array*.

Sure, I'll could try writing MR shader, I have written a MR shader accomplishing color per vertex shading using particle the system in a softbody mesh in the past.

QUOTE
Or you can just use many many copies.

Yeah, then I could just go with regular instancing rather than particle stuff. But this approach will not scale well with large number of objects

QUOTE
*i think i have a early proof of concept (its hard to use but it does work) somewhere lying around you can get it if i find it....

Yes, please do share if you find it.

Thanks for your help and for moving the post to the right forum as well.
Cheers

[joojaa]

QUOTE(amitc @ 07/11/09, 06:47 PM) [snapback]311320[/snapback]
Yes, please do share if you find it.

Well i can see it form the logs soi prettymuch allmost certainly know where it is. Thing is i have summer vacation comming up in week so ill look in then.

Its not much but atleast saves you some time, i mean its a proof of concept i used back in 8.5
QUOTE
Sure, I'll could try writing MR shader, I have written a MR shader accomplishing color per vertex shading using particle the system in a softbody mesh in the past.

In taht case i have tip for you autdesk exports the entire particle systems data (or well just the basics) to custom binary field you can read the data from there then just in init ask what the name of each instance is and calculate the index form that. (they document it in the devkit folder)

PS: to be honest i dont know WHY autodesk wont want to eanble the particle info node catch info for instances

[amitc]

QUOTE(Joojaa @ 07/11/09, 08:50 AM) [snapback]311324[/snapback]
Well i can see it form the logs soi prettymuch allmost certainly know where it is. Thing is i have summer vacation comming up in week so ill look in then.

Great thanks, but I woud'nt want to ruin your vacation for this.

QUOTE
In taht case i have tip for you autdesk exports the entire particle systems data (or well just the basics) to custom binary field you can read the data from there then just in init ask what the name of each instance is and calculate the index form that. (they document it in the devkit folder)

I am bit confused how does knowing the index of instance help.

I have a very good understanding of PDC file format and have the necesary tool to read and write custom PDC files.
I piece I am missing is how can use the say the rgbPP (color per particle) info to shade instances on pre particle basis.
I'll also dig into the devkit to see whats in there.

Again thanks for the tip.

[joojaa]

QUOTE(amitc @ 07/11/09, 10:15 PM) [snapback]311335[/snapback]
I am bit confused how does knowing the index of instance help.

You can read it form the pdc but autodesk embeds this in the mr stteram, make a particle give some pp colors export it as mi, the file now contains:

CODE
data "particleShape1:ptdata"
1636 [
'6179614d03000000010000000400000029000000390000000000000039000000'
'03000000b400000000000000b400000000000000b400000000000000b4000000'
'00000000b400000001000000dd00000001000000060100000300000081010000'
'0000000082010000000000008501000086010000870100008801000089010000'
'00000000000000000000000000000000000000008a0100008d01000090010000
....

(this data is used by geomery shader but no reason why you cant use it for your instances)

This binary data is described in the devkit folder but basically ist a list taht contains velocity,color etc for the particles. So now all your shader need to do is read the data, and pair it with index you obtained form isntance name.

Again make a instanced file export mi and it becomes clear what mayas up to. In general it actually pans out to read the mi files every now and then.

So: now you have the data the index and the color all you new need is shater that querries shading isntance name, tekes the index looks up list and outputs color, done.

PS: Each item gets a separte instance so you dont need to do the querry for index for every sample just the init of shader for each instance (its a bit heavy)
QUOTE
Great thanks, but I woud'nt want to ruin your vacation for this.

You really think i can be without a computer for 4 weeks? In any case its just a matter of copying a file, it just that my old computer is not here. Im going where it is anyways on my vacation.

[amitc]

QUOTE
So: now you have the data the index and the color all you new need is shater that querries shading isntance name, tekes the index looks up list and outputs color, done.
PS: Each item gets a separte instance so you dont need to do the querry for index for every sample just the init of shader for each instance (its a bit heavy)

I see, this would need some work, more than I anticipated. But, well things are not always easy.

QUOTE
In any case its just a matter of copying a file, it just that my old computer is not here. Im going where it is anyways on my vacation.

Cool, will look forward to see what you find

QUOTE
You really think i can be without a computer for 4 weeks?

Yeah, I used to be in the same boat in the past, but now I am not so sure.
Anyways have fun!

[thnkr]

PLEASE log a sug with Autodesk. When I was there I tried to get it done, but I always found that there were simply not enough user requests to justify spending the resources. This just didn't make it high enough on the priority list.

[joojaa]

I dont need this anymore (and yes its been logged allready waaay back). In any case itsd need to be pretty much more flexible than its now. To ne honest id rather have them allow me to code plugins that affect the exportation business for custom shapes better. I mean the way we do it now is ok but not perfect it should be trasparent to users.