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

Colin Doncaster colin.doncaster at rsp.com.au
Wed Mar 22 18:58:44 EST 2006


Hey dude -

No worries, that's what the unix sop is handy for.  You can pipe your  
current objects data to an external script, check out the help for it  
and there is a user note from lucas that describes it in better detail.

So you'd have a python script that accepts houdini's geo ascii format  
as input ( from stdin ) and you can parse and format your data into  
the .mi file.  If this is in your opnetwork ( I'd say make it your  
render op ) you could then have it cooked on every frame prior to  
the .mi file being written.  Because it's in your SOP level it will  
be on a per object basis, you should be able to get all the custom  
attributes in the geo file.

To get the format spec for the geo format check out

$HFS/public/GPD

I don't think that the Attribute's you define on a SOP level are  
passed through to the mi.  You can add some input parameters to you  
script that handles specific cases for these attributes you know about.

I'm tired, so I'm not to sure if that makes sense.

Cheers - col.

On 23-Mar-06, at 10:41 AM, Guy Rabiller wrote:

>
> 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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>>> Sidefx-houdini-list at sidefx.com
>>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>
>> -- 
>> Colin Doncaster Some Guy -- colin.doncaster at rsp.com.au
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--
Colin Doncaster Some Guy -- colin.doncaster at rsp.com.au
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