[Sidefx-houdini-list] houdini -> mental ray user datas

Guy Rabiller guy at alamaison.fr
Wed Mar 22 18:41:22 EST 2006


Thanks Colin,

that's a start for me, very interresting. I'll investigate.

On a scene basis I can surely feed my custom datas through this 
inclusion mechanism.

Now I have to figure out how to make the link between those datas and a 
specific object instance.
By any chance, do you know if this mechanism is available on a per 
object basis ?

Looking at the Shading tab of a model, there is a mental ray sub-tab, 
where we can set mental ray shaders.

Idealy, I'm looking for the same idea but for the object description 
itself, or mental ray 'attributes', may be a SOP node in wich we could 
set mental ray attribute for this object ( or light, or camera, etc.. )

For instance a mental ray object Instance has attribute such as 'hide' 
(on/off), 'shadow' (mode) and even 'data' ( data name ), the one I'm 
interrested in.

May be I'm just overcomplicating things ? If I put an Attribute SOP and 
use 'hide'/'on' it will be transmitted as this to the mental ray 
instance description ?
Could it be that simple ?

I didnt try real exemple yet, I'm just trying to globaly figure out the 
right way(s) to reproduce ( and extend ) the type of workflow we 
currently have with XSI / mental ray.
( still very new to Houdini )

--
guy rabiller | 3d technical director @ LaMaison


Colin Doncaster a écrit :
>
> hey guy -
>
> each model has the pre and post include script which does get written 
> out to the .mi file.  You could write a pre-frame script ( in the 
> mental ray ROP ) that runs a script to generates an .mi file for that 
> frame and then set the pre/post include to that output.
>
> You can open a command port or stuff all the relevant object 
> information onto the command line to get scene data.
>
> It's ugly ( ish ) but it should work.
>
> Oh, the other thing that occured to me, if you put a unix sop at the 
> end of your sop network you could then pipe all the geometry data to a 
> script that formats it into the per frame .mi you want which means you 
> won't have to worry about the pre frame script in the output ROP.
>
> Just some thoughts.
>
> Cheers - colin.
>
> On 23-Mar-06, at 1:52 AM, Guy Rabiller wrote:
>
>> Hi,
>>
>> regarding mental ray rendering from within Houdini, is there any 
>> built-in mechanism to transfert "user-datas" to mental ray 
>> scenes/shaders ?
>>
>> In XSI for instance, there are what so called "UserDataBlobs" at a 
>> scene or object level, wich can be 'filled' by ascii datas from 
>> script or ascii/binary datas from c++ plugins.
>> Then at render time, XSI automatically send those datas as user datas 
>> ( miQ_OBJ_DATA.. ) attached to the object containing the UserdataBlob.
>>
>> Is there such mechanism in Houdini ?
>>
>> If not, what could be the best way to handle this, to enable user 
>> datas communication between Houdini and mental ray ?
>>
>> Thanks in advance.
>>
>> -- 
>> guy rabiller | 3d technical director @ LaMaison
>>
>>
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>
> -- 
> Colin Doncaster Some Guy -- colin.doncaster at rsp.com.au
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