[Sidefx-houdini-list] Grouping Outside Faces

Sean Lewkiw seanl at rainmaker.com
Thu Jan 3 14:09:50 EST 2008


Haven't used DOPS in a long time, but I've done this before somehow.  
Can you take your DOPs sim, pipe it into the second input of a point 
SOP, and your original, un-simmed rest geo with all of your nice front 
facing groups into the other, and then assign its point positions using 
$TX2, etc, (and if this works, then build a VEX version).

Sean



Edmond Earl Smith wrote:
> Sure, no problem.  I need to texture the faces pointing out with a 
> different texture than the inner ones.  Just like bricks smashing with 
> dirty outsides but clean inner brick textures that have not been 
> exposed to the elements.  I need to do this procedurally.
>
>
> Marc-Andre Carbonneau wrote:
>
>
>   
>> Hi Edmond,
>>
>> I am completely green to Houdini so I cannot help you but I am curious 
>>     
> about why you want to make a selection of the inner faces. What are you 
> going to do with it exactly? What are you trying to achieve?
>   
>> Thank for easing my curiosity! ;)
>>
>> Marc-Andre
>>
>> -----Original Message-----
>> From: sidefx-houdini-list-bounces at sidefx.com 
>>     
> [mailto:sidefx-houdini-list-bounces at sidefx.com] On Behalf Of Edmond 
> Earl Smith
>   
>> Sent: January 3, 2008 1:13 PM
>> To: sidefx-houdini-list at sidefx.com
>> Subject: Re: [Sidefx-houdini-list] Grouping Outside Faces
>>
>>
>> Hey thanks for the help.  I got something to work that's a little like 
>> your suggestions.  I just had to do some fancy grouping.  One of the 
>> bigger challenges is going to be getting this information to transfer 
>> through DOPS and back into SOPS.  DOPS reassigns the RBD glued objects 
>> so that each group is a separate RBD object.  When it does this it 
>> reassigns the faces per object, so it's not like I can even create a 
>> group and try and reference the faces later once they've been 
>> simulated.  I have no clue how to grab these inner faces once the DOP 
>> sim has gone through.  Any suggestions? 
>>
>> Thanks again so much,
>> Eddie
>>
>> François Duchesneau wrote:
>>
>>
>>     
>>> Ok, here's how to do it. Forget the first method because I thought the 
>>> PolyExtrude would promote the points inside a group to the 
>>>       
>> corresponding 
>>     
>>> extruded points. Anyway it's better the following way.
>>>
>>> For this, I assume your inner faces are all in pair of two because you 
>>> want to have many cubes from the extruded grid.
>>>
>>> 1-Create an other PolyExtude Sop but check "Remove Shared Sides" on 
>>>       
>> this 
>>     
>>> one.
>>> 2-Append an AttribCreate after the second PolyExtrude and create a 
>>> primitive attribute, let's say "inner" and set the value to 1.
>>> 3-Append an AttribTransfer after the first PolyExtrude and set the 
>>> "Distance Threshold" to 0.001 for example.
>>> 4-Create a Group Sop with "Group by Expression" set to $INNER==0
>>>
>>> ... and you're done. You can also look at an example file I've posted 
>>>       
>> on 
>>     
>>> the Exchange called "Transparent Shattered Glass" that uses an other 
>>> mechanism that put every coincident faces into a group without having 
>>>       
>> to 
>>     
>>> duplicate the PolyExtrude.
>>>
>>> François
>>>
>>> François Duchesneau wrote:
>>>       
>>>> I'm sorry. I answered too quickly without cross-checking what I was 
>>>>         
>> saiying.
>>     
>>>> I think you'll have to do an intersection boolean operation with the 
>>>> "extrudeSide" group from the PolyExtrude.
>>>>
>>>> I test that and let you know.
>>>>
>>>> François
>>>>
>>>> François Duchesneau wrote:
>>>>   
>>>>         
>>>>> You can append a Group Sop before the extrude, set the type to "Point" 
>>>>> and go in the "edge" tab and check "Unshared Edges". This creates a 
>>>>> group of all points being the boundary. Invert the group with a 
>>>>>           
>> boolean 
>>     
>>>>> operation inside that Group Sop to get all points that are not a 
>>>>>           
>> boundary.
>>     
>>>>> All the edges in that group will be included inside the geometry after 
>>>>> the extrude.
>>>>>
>>>>> François
>>>>>
>>>>>
>>>>> Edmond Earl Smith wrote:
>>>>>   
>>>>>     
>>>>>           
>>>>>> Hello everyone, I have a fractured object that I create by extruding a 
>>>>>> grid and partitioning the pieces.  I would like to group just the 
>>>>>>             
>> faces 
>>     
>>>>>> that are "inside" the object.  Much like the group extrudeSide when 
>>>>>>             
>> you 
>>     
>>>>>> use the polyextrude but without the outer faces, just the inner ones.
>>>>>>
>>>>>> thanks,
>>>>>> Eddie
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>>>>>>   
>>>>>>     
>>>>>>       
>>>>>>             
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>>>>>   
>>>>>     
>>>>>           
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Sean Lewkiw
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