[Sidefx-houdini-list] Pixel Coverage Shader

Jeff Wagner jeff at sidefx.com
Mon Jun 7 14:34:56 EDT 2010


On your Mantra ROP Output Driver, add the following Render Property from 
the Edit Parameter Interface dialog:

Mantra10.0 > Output > "Generate Op Ids for objects" (vm_generate_opid)

Then add an Output Image Plane using the default "Node Id" in the VEX 
Variable right hand side menu.

When you render, you will get the id of the object as a separate channel 
(aov). I think that's what you are after.


Tip: in the Op_Id image plane preferences, you can set this to 16 bit 
float as well as set the Pixel Filter to "Closest Sample Filtering". The 
latter will remove any anti-aliasing from the edges of the objects 
making for more consistent comps at the edges. Get rid of the 
anti-aliased bogus data.

Warning: if you re-sort your objects, remove and add others, the id 
channels may change which will require you to rework your comp. Make 
sure to add notes or rename nodes in the comp to tie in to the objects 
in the scene just in case.


-jeff

Alvaro Castaneda wrote:
> I guess if you already have material ID pass, (separated by color)
> you could just find that edge in any compositing app, using that channel as
> the alpha.
>
>
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>   On Fri, Jun 4, 2010 at 6:31 AM, Daniel Jenkins <thedj28 at googlemail.com>wrote:
>
>   
>> Hi all,
>>
>> I'm currently looking into how to get a pixel coverage pass out of mantra (
>> in the style of http://www.sigillarium.com/blog/lang/en/379/ ) but I can't
>> seem to find much information about it or how to access that information
>> from the renderer. Im just researching into some kind of work-around/hack
>> and was wondering if anyone here has had some experience with this and
>> could
>> point me in the right direction. Any help/wisdom would be greatly
>> appreciated!
>>
>> Cheers,
>>
>> Dan
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