Surface particle emission on Zbrush displaced surface voodoo

[fbonniwell]

Hello All,

I have a model with a very high detailed displacement map from Zbrush. The model in Maya obviously has a low res model that depends on the displacement maps for details at render time. Working with particles based on this surface has become a challenge.
We are using particle texture emissions with a creation expression goalPP and goalU = parentU, goalV = parentV to keep the particles on the surface. Is there a way emit particles at render time so the particles are on the displaced surface?
Or is it possible to set the initial state and cache the displaced particles so I can review the sim before submitting to the render farm?

Thanks,

F

[joojaa]

Is there a way emit particles at render time so the particles are on the displaced surface?

Not really. (that is to say its possible but not without you doing some development yourself).

But it is possible to diplace the goal based on the texture value. Tough its SLOOOOW.

Or is it possible to set the initial state and cache the
displaced particles so I can review the sim before submitting to the
render farm?

Yes just do a disk cache.

[fbonniwell]

Not really. (that is to say its possible but not without you doing some development yourself).

But it is possible to diplace the goal based on the texture value. Tough its SLOOOOW.

[quote=fbonniwell ]

Or is it possible to set the initial state and cache the
displaced particles so I can review the sim before submitting to the
render farm?

[/quote]

Yes just do a disk cache.

Thanks for the input! Can you explain in more detail about displacing the goal based on the texture value?
Would this be based on the displacement value?

Thanks,

F

[joojaa]

Make a per particle expression that reads the surface point position and normals+ binormals, then querry the uv location on your surface and get the displacement value then move your particles position up along the normal by that value.

The only problem si that querying the uv value of the current position is a bit slow to say the least. So i wouldt attempt to do this if you had more than say 500 particles as it would take AEONS for you to solve the simulation. So if you are setting goal uvs yourself then your in luck otherwise your not so lucky

[fbonniwell]

Right! Makes sense!
How about a goal offset? I found this chunk of code in a the dynamics thread.
I'm a little confused where he got ".height" from.

vector $fh = ps.height*(file1.outAlpha);
ps.goalOffset = <>;

Thanks,

F

[joojaa]

http://www.romainrico.com/archives/277