[Sidefx-houdini-list] Motion blur with gather()?

Andy Nicholas andy at andynicholas.com
Tue Oct 14 20:47:44 EDT 2008

Hi Pablo,
Thanks for the idea. As it happens, I've already started looking at super
sampling the particle animation, say, 10 sub-steps every frame by linearly
blending between this frame and the next. That'll hopefully provide me
with smooth motion.

You might be interested to know that I'm using data from our old friend
Realflow. I've had a lot of fun tracking groups of particles between
frames using the Realflow based ID which remains consistent (the Houdini
point order changes on each frame). I'll have to see if I can find some
time to write an article on it as it's a great example of using geometry
to do data processing, not to mention VOP SOPs.

Anyway, I guess I was hoping there was some nifty little render attribute
I could turn on somewhere that'd let the gather() loop work across the
frame time. Oh well :-)



> Mmm, one dirty solution, very dirty I admit, in case you are converting
> your
> fluid with the PArticle Fluid Surfacer, as I guess, I think you can use th
> Trail SOP to bring the geometry of the previous frame into your current
> frame and then send rays agains both of them, maybe it can work, but I
> have
> said is a very dirty hack.
> 2008/10/14 Andy Nicholas <andy at andynicholas.com>
>> Hi,
>> Thanks for all the info on making my wetmap shader work! Unfortunately,
>> I've got another related problem that'd be great if I can pick some of
>> your brains on.
>> Since my fluid moves quite quickly it leaves occasional gaps on the
>> wetmap. If I can get it motion blurred, it'll be sorted. Is it possible
>> to
>> somehow detect the motion of the fluid inside the gather loop? Just to
>> be
>> clear, I don't mean picking up the velocity attribute, just that I'd
>> like
>> the gather() samples to realise that they should be stratified over time
>> so that I can average them together to produce the blur.
>> Is it possible to set this up somehow in the shader?
>> Thanks
>> Andy
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> --
> Un saludo
> Best Regards
> Pablo Giménez

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