[Sidefx-houdini-list] POP Sub Frame emission problem

craigleehoffman at aol.com craigleehoffman at aol.com
Mon Oct 26 21:29:45 EDT 2009


 
I think I figured it out- and Houdini is doing the right thing.  

In my case everything is moving fast, including the camera, so I have to Inherit the Velocity to keep the trails up with the object the way I want (and get proper motion blur, etc.), but the Velocity Attribute doesn't change smoothly in between frames, thus causing a discontinuity when particles are emitted from 1.9 to 2.0, with inherited Velocity that jumps at that point.

Doh!

Unfortunately the Cache SOP will do subframe blending of the position, as will the TimeBlend SOP, but neither address smoothly blending Velocity attributes to avoid such discontinuities.  I guess I could stuff V into P and do a TimeBlend and then stuff it back into V...  :)

-Craig

 

 

-----Original Message-----
From: François Duchesneau <sidefx at trinix.ca>
To: sidefx-houdini-list at sidefx.com
Sent: Mon, Oct 26, 2009 6:47 pm
Subject: Re: [Sidefx-houdini-list] POP Sub Frame emission problem










I'm not apply to you but are you sure the subframes you see manually are 
the same that are evaluated by pop. For example, if you're oversample 
10, make sure that you've got the proper point positions at 1.1, 1.2, 
1.3 etc

François

craigleehoffman at aol.com wrote:
>  
>
>  The Timeblend SOP does that, but I have already taken care of it.  I can turn 
off Integer Frames in the Display and see the source points move smoothly in 
between Integer Frames, so I know the input to the POPNet is subframe capable.  
>
> The particles seem to being birthed in a subframe way (not all on top of each 
other, but along the path the source points trace), but they seem to be emitted 
only in a small portion of the IntraFrame time.  I tried using Impulse Birthing 
as well as Constant Birthing with different settings to birth the correct number 
of particles for the Oversampling setting.
>
> Weird.  I know this used to work.
>
> -Craig
>
>  
>
> -----Original Message-----
> From: Andrew D Lyons <tstexture at gmail.com>
> To: sidefx-houdini-list at sidefx.com
> Sent: Mon, Oct 26, 2009 3:13 pm
> Subject: Re: [Sidefx-houdini-list] POP Sub Frame emission problem
>
>
>
>
>
>
>
>
>
>
> Are you reading source geometry in using a file SOP? If so - you need
> to use a blend SOP to get in between frame geometry. (I know there's
> an otl up there that does that...)
>
> Cheers
>
> 2009/10/26  <craigleehoffman at aol.com>:
>   
>> But that results in particles only being birthed at integer frames- like 
>>     
> having no oversampling on for birthing.  I am trying to birth between frames 
in 
> a nice smooth way.  The bunching when oversampling is on usually happens 
because 
> the geometry doesn't move smoothly between frames, but in my example it does.
>   
>> I know this used to work...
>>
>>
>>
>>  -Craig
>>
>>
>>
>> -----Original Message-----
>> From: Ben Frost <benfrost3d at gmail.com>
>> To: sidefx-houdini-list at sidefx.com
>> Sent: Sun, Oct 25, 2009 2:37 pm
>> Subject: Re: [Sidefx-houdini-list] POP Sub Frame emission problem
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> If I use impulse (per cook) birthing I normally divide this by the number of
>> oversamples to avoid the sort of thing your talking about (bunching of
>> particles)..  err not sure if this is your problem.. but it's my two pennies
>> worth :)
>>
>> cheers
>>
>> ben..
>>
>>
>> 2009/10/25 <craigleehoffman at aol.com>
>>
>>     
>>> I can't seem to get this to work properly (H10.0.374).
>>>
>>> I can verify that the points going into my POP Network move smoothly in
>>> between frames by turning off "Integer Frame Values" in the "Global
>>> Animation Options".   But with an "Oversampling" of 9 and "Accurate Births"
>>> checked on on the Source POP, I get 9 particles emitted per point fairly
>>> close together and then a big gap and then 9 particles again, rather than
>>> the 9 spread out evenly over the whole frame.
>>>
>>> They do seem to be spread out in a subframe way, creating a non-overlapping
>>> arc, but they are just not being emitted over the whole distance the
>>> emitting point travels in a frame, leaving gaps.
>>>
>>> Any ideas what could be causing this?
>>>
>>> Thanks,
>>> Craig Hoffman
>>> _______________________________________________
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>>> Sidefx-houdini-list at sidefx.com
>>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>>
>>>       
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>   
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