[Sidefx-houdini-list] Swimming noise displacement

Dan Wills gdanzo at gmail.com
Sat Jul 7 06:24:21 EDT 2012


H12.0.634 on linux here, and sorry I'm probably not much help because it
seems to work fine for me.

It looks like mantraSurface is set up to do the right thing with the
built-in noise displacement. It contains a turbnoise node, inside the grey
netbox near the bottom of the network (as Floyd suggests), labeled
"Displacement". The noise is looked up using a 'Rest Position' node, which
is (by default at least) set to 'Object Space', so it shouldn't be affected
by camera movement, unless there is something special about your geometry.
Maybe you do have a 'rest' attribute that is moving?

Is the geometry definitely locked to its local space? (in other words, if
it is moving then it is because of Object level transformation, not SOPs
level deformation)

One thing I wondered was whether the swimming you are perceiving might be
to do with the mantra setting 'Sample Lock'. Is the swimming perhaps only
in the very highest frequencies of detail (ie per-pixel level)? If so, you
might like to do a test with 'Sample Lock' disabled and see if what you
thought was noise was actually a locked sampling pattern.

Sorry I'm not much help, but you might need to provide a little more detail
about what's going wrong :).
Dan

On Sat, Jul 7, 2012 at 1:56 PM, Floyd Gillis <floyd at afcg.com> wrote:

> Hi Francois,
>
> Thanks for the suggestion... unfortunately I'm not too familiar with
> VOP-land and would need much more detailed instructions on making the
> changes.
>
> Cheers,
>
> Floyd
>
>
>
> On 07/07/2012 1:00 PM, François Duchesneau wrote:
>
>> Have a look inside the shader and find what drives the displacement
>> noise, below in a gray network box if I'm not wrong. From there you can
>> always use P and transform it to world space with a Transform Vop and plug
>> that into the P plug of the noise. But I'm surprised that the rest doesn't
>> work, I would think that this shader has that built-in.
>>
>> François
>>
>> Floyd Gillis wrote:
>>
>>> H12.0.626 on linux
>>>
>>> Have enabled "Noise", (without "True Displacements"), under the
>>> Displacement tab of a "Mantra Surface Shader".
>>>
>>> Also have an animated Y offset to give a moving ripple effect through
>>> the geometry.
>>>
>>> Everything works fine until I move the camera... which causes the noise
>>> to swim through the geometry.
>>>
>>> Adding a rest SOP doesn't seem to have any effect.
>>>
>>> Any other suggestions on how to keep the noise fixed to the geometry
>>> when the camera moves?
>>>
>>> Thanks
>>>
>>>
>>>
>>>
>>>
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>>
>
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