[Sidefx-houdini-list] Swimming noise displacement

Christian Waite christianjwaite at gmail.com
Sat Jul 7 19:49:00 EDT 2012


If its swimming when the camera is moving its because the p position is
taken from the wrong space. In shaders it's using the camera point
position, you need to lay down a transform node (in the shader) and convert
it from current space to work space before going into the p input of the
noise shop...

C

On Saturday, July 7, 2012, Floyd Gillis wrote:

> Dan & Francois,
>
> Thank you for your help.
>
> - Did not see a grey netbox near the bottom of the mantraSurface network.
> - Geometry is stationary, simple polys with a locked SOP as 2nd input to
> the rest SOP.
> - Sample lock was disabled.
>
> There might me something else I'm missing or doing wrong... will be back
> in the office later today to do more testing.  If I still can't get it
> working I'll send more details or a simple hip file.
>
> Cheers,
>
> Floyd
>
>
> On 7/7/2012 7:24 PM, Dan Wills wrote:
>
>> 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 <mailto:
>> 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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