Hi all !

So I'm doing this animation where I have a box of dry sand and I need to animate a logo as if it's drawing into the sand (like you would kind of draw something with your finger at the beach).

So I've done a first test with a simple torus animating along his radius onto the sand and that worked all fine.
But now that i'm trying with the animated logo it kind of works but it is very jumpy and don't recognise the shape so well. The way I'm animating the logo is using a trace on a PNG sequence of my logo animation and then extruding it and make it draw on top of the sand and I'm using the extrude as a collider.

So my guess right now is that the extruded shape out of the trace isn't really recognise as a ‘'solid’' mesh and therefore it's not really working.

Sorry I'm really new to Houdini and I'm sure this is something that can easily be fixed, maybe you guys know a better way to make my logo animation interact with the sand ?

Thanks in advance for your answers.

This is where a .hip file is a good help for figuring out how you've got it setup…

Triangle collision detection requires constant topology, so if you are doing a trace + extrude you probably don't have that.

You thus want to make sure it is using volume collision detection and verify those volumes are high enough res to resolve the shape you have.

If you are using the Deforming Object shelf tool, it assumes constant topology.

In the collision source, turn off Blend Between Frames and Velocity as these will be confused by changing point counts. Display the VDB output and make sure you are resolving the shape over your sequence.

For best results, especially with fluids, you want to generate the correct velocities on the collision geometry. But sand should be able to stumble by without that.

Hi Jlait and thanks for your quick answer, I'm going to try out your solutions and see if that works, for now i've broken down my logo which is symmetrical in 4 different shapes instead of one which works already better but it's not perfect. I haven't tried the deforming Object shelf tool but will do an see what happens. You are definitely right that the shape is not closed so that is probably what is causing troubles.

I'll keep you posted

Cheers

Alright it's all solved using deforming object instead of static worked great ! Thanks for the help

I'm having a similar issue.. Can't get the grains to act normal inside a hourglass! they just move erectly because of the movement of the hourglass..

jlait
This is where a .hip file is a good help for figuring out how you've got it setup…

Hour glasses may often cause problems if you don't make them hollow. You may need to invert the SDF for the collider.