Scattering points on changing topology geo

[edgem]

Hello all,

 

I am in a process of scattering points into a changing topology geo. I have read things on the message board but did not find the solution... Points position are changing every frame. I tried different things but is not working The solution that I found here seems not to be adapted to a changing topology shape and that's beyond my houdini knowledge. I guess I would not have any issue scattering points on a deforming geo but a changing topology geo makes things harder.

 

Is there any solution to deform these points to match the shape ?

 

Currently, the shape (a tree) is growing and reach its final topology at the end of the framerange..

 

Does anyone know how to tackle it ?

 

Thanks guys

Edited November 19, 2014 by edgem

[loopyllama]

You can scatter points on a non-deforming object then ray those points back on the topology-changing object. This is not perfect be may enough for you. Try to have as much animation on your scatter object as possible, i.e. have your tree grow up without changing topology, then scatter on that before raying the points on the topology-changing tree. The closer your non-topology changing object is to your topology changing object, the less change there will be when raying the points each frame.

[Magasul]

I am new to Houdini too, but my approach would be this:

1. Save out the final state of the tree with it's final topology.
2. Scatter points on it (A)
3. Scatter points on the growing animation. (
4. Transfer color attribute from the growing points ( onto the final points (A).
5. Delete the uncolored group.

[edgem]

Hello guys,

 

Thanks for the replies

 

@loopyllama : sadly, the animators gave me the model so it is currently not possible to have a non deforming geo because of deadline...

 

@Magasul : looks great but I am not too sure about step 4 and 5 ? 

 

Thanks

[Magasul]

So you add a color SOP onto the growing scatter points. 1 0 0 (red)

Then as they grow, you add an attribute transfer that transfers the color onto the final scattered points.

Then you delete by expression and delete the points from the final scatter that doesnt have the red color transfered to them.

 

With this as the tree grows, it gives more and more points color and thus undeleting them.

[loopyllama]

hand animate a very simple proxy object to grossly match the overall animation. add a uv unwrap. scatter on the deforming hand-animated proxy object with alternate attribute uv and alternate bias to 1. ray the points back to the deforming geo with minimum distance.

[edgem]

Okay so I have tried and....sadly won;t work as expected 

 

@Magasul : the color trick seems to work but ... the animation does not start accordingly and does not follow the whole animation of the original model.

 

If you guys can check or post a hip file would be great

 

Here is the link to the geo

 

https://www.dropbox.com/s/cen2xxpuxf80mg3/P0080_treemodel_v007.abc?dl=0

 

 

The thing I don't understand is why the points change position since the geo count is the same all through the animation. The scale does change though. I hope this great community could help me answering that question.

 

 

Thanks again for tacking this issue

Edited November 20, 2014 by edgem

[loopyllama]

Here is the setup I described, with a teapot geometry test case:

 

scatter_on_topology_changing_object.hip

[loopyllama]

Your topology does not change. You only need to do a scatter.

Changing topology means that you gain/lose vertices/points/primitives. If you middle mouse on your geometry you will see the topology does not change.

 

Just reimport the alembic file in the attached example:

 

simple_scatter.hip

[edgem]

Thanks loopyllama,

 

The scene with the teapot is fantastic.

 

I also checked the last hip file and I was sure I was doing the same thing as you. As simple as that.....O_o but acutally I checked "scatter on primitive area"  on the  scatter SOP, that's why it did not work...

 

 

 

Thanks anyway for taking your time

Edited November 23, 2014 by edgem

[edgem]

Now, how would you noise the scattering points based on that geometry ? I would like to use Vopsop to manipulate noise but the points keep changing every frame. That is the main issue actually since I want to break the pattern a lot. Can you give me any advice on that ?

 

Been trying to use rest position. It works but the first 10 frames at jittering and I can't see why

 

 

 

 

Thanks

Edited November 23, 2014 by edgem

[3__]

Try putting P into Cd via point sop,

Putting uv into P via another point sop,

Scatter points on a 1x1 grid, translated to -1 in Z and with normals as [0,0,1],

Ray the points onto the unwrapped geo, acquire Cd, add rayhitgroup,

Discard points not in rayhitgroup,

Send Cd to P via point sop... 

Good luck

[edgem]

I think something is wrong with my paint SOP node.

 

Here is the hip file

 

https://www.dropbox.com/s/vq6vdrhtjz2jho6/scatter_test.hipnc?dl=0

 

For the geo, it is the same alembic file I have provided earlier

 

I guess I am doing it wrong somewhere. The jittering are happening from frame 1041 to 1060 approximatively and it seems that as soon as I use scatter SOP after color (for BG color) and paint SOP to define my zone, it always seems to jitter at this framerange... The problem disappears when I disable the color SOP though

 

Thanks

Edited November 23, 2014 by edgem

[Rainroom]

I have attached the fixed .hip file. Please check if it works. Also make sure that you replace my alembic file path with yours.

scatter_test_fix.hipnc

Edited November 25, 2014 by Rainroom

[edgem]

Nice thanks for the fix

 

Now I am having some serious issue about substepping particle emission 

Here is a screen of what happen. 

I am getting these weird pattern. I tried increasing Substep in Pop and play with interpolation and birth time but to no avail... 

 

Is the interpolation of the geo causing the issue ?

Edited November 25, 2014 by edgem

[Rainroom]

Have you tried time blend sop for your source geometry?

[edgem]

yes TimeBlend does not help...that's why I was asking about some other issue than interpolation :0

 

Here is the hip file using an old scene i have worked on

 

https://www.dropbox.com/s/p2sne2dlqlanifc/substep_issue.rar?dl=0

Edited November 25, 2014 by edgem

[edgem]

I managed to get through this by scaling the geo. The sim looks more realistic now...

 

So I guess scene scale was the problem ?

Edited November 25, 2014 by edgem

[loopyllama]

Try setting the POP Source "Interpolate Source" under Birth to something other than "None"

 

check out the Pop Source help for more info...