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    James Earnest

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  1. @Librarian Thanks, that looks interesting. Any chance for a hip file though? It's kinda hard to figure out what's going on without diving into some of those nodes.
  2. Hi, I'm trying to create an effect like the one here: https://player.vimeo.com/video/290076899 My approach so far is using a cross product of the point normals with a default up vector, and rasterizing that as a velocity field that the points are advected by. But this results in a simple rotating motion, rather than swirling around the mesh: The caption in the video says "POP VOP + Crowds", which is obviously not too informative. I don't think the Crowd part of it is too crucial if I'm not using animated agents, so it's mainly the POP sim that I'm trying to get right. Does anyone have some tips how to approach this? HIP file also attached. Thanks! POP_Letter.hip
  3. Hi, I have a FLIP color mixing situation, but I'm using more than two colors. Let's say four, for now. My basic approach is this: 1) Create four attributes on all source particles, so a single particle would have for example all of these: f@blue =0; f@green = 0; f@yellow = 0; f@red = 1; 2) Find a way to mix the attributes during the sim 3) Transfer these attributes to the mesh, and then modulate the shader color with this input. I'm looking for advice on how to get them mixing correctly in the sim. Attribute Transfer in a SOP solver might play a role here, but the issue is I need to find a way to normalize the influence of these attributes so they'd always add up to 1. That is, if one attribute increases, its influence is subtracted from another. Kind of like when painting weights in rigging. I've watched a bunch of tutorials on color mixing, but they're always with just two colors, which simplifies things greatly. Been wrestling with this one for a while and I'd really appreciate any ideas on how to achieve this. Thanks very much for any advice!
  4. Hi, I want to blur some attributes across adjacent points, but the Attribute Blur SOP only seems to work on connected geometry. I tried Attribute Transfer and Point Cloud Filter, but they're both really slow. Is there any other option here? Thanks!
  5. Hi, I have a FLIP source, and I'd like to control which particles get simulated by using a group - i.e. create a Group node with a bounding sphere and animate its size, so that only points inside that group get simulated. I have the basic setup, using a POP Group node with Preserve Group checked on. Then I set @v to {0,0,0} on all points outside that group. It kind of works, but the boundary is kind of soft, and points from outside keep creeping in and getting simulated. Maybe there's something else I could use? Something similar to the @active attribute in Bullet? Hip file attached. Thanks for any suggestions! Activate By Attribute.hip
  6. Posted by mistake, sorry
  7. Hi, Can anyone explain what the temperature attribute does in FLIP sims? Quite surprisingly, this attribute is not documented in the help files for the FLIP object. Thanks!
  8. Hi, Forces in DOPS tend to accumulate and get stronger and stronger over time. I guess that makes sense in a way, but in many situations this is not wanted. For example, when using a Curve Force or POP Axis Force - you often want the force to affect your objects predictably and not lose control. Is there a way to limit the accumulating behavior when using forces? I often resort to VEX/VOPS to control velocity directly, but it can get pretty hard. Forces offer a lot of handy behaviours, I just wish they were more controllable - any tips? Thanks!
  9. Thanks, but I get the same issue when fracturing manually with the Voronoi Fracture node.
  10. Hi, I have a model that renders fine unfractured, but once I've fractured it, I get shading artifcats from bad normals. It looks like Houdini is inferring normals for the new vertices by interpolating between neighboring ones, but it's not looking right. I've tried using an Attribute Transfer SOP to take the normals from the pre-fractured model, and it helps a little but doesn't solve it completely. Also tried the cupsing settings on the Facet SOP and Vertex SOP. I'm stuck. Does anyone have an idea how to fix this? I'm not doing any fancy fracturing, just the RBD Material Fracture node. Thanks!
  11. Hi, Is there a way to scale the collisions in bullet sims, like you can in FLIP? I have a slow-moving collider, but I want the impact it creates to be more forceful. Thanks!
  12. Hi, I have some fractured geometry in SOPS. I want to animate the geometry in SOPS, and have that motion inherited within DOPS, so that the geometry breaks when it encounters collisions along its path on the SOP animation. In some programs this is called a Kinematic rigid body - you control the movement of the object as a whole using traditional keyframes, and these keyframes give the simulation implicit velocity data to base the dynamics off of. Does anyone have an idea how this can be done? Thanks!
  13. Hi, I'm confused about what the Time Scale parameter on different solvers actually does. The documentation is kind of vague - "scales the timestamp used by the solver". But it doesn't just slow down the sim, it actually changes the behavior in ways that I haven't been able to consistently understand. So I'm wondering what I'm actually telling the sim to do by changing this parameter. Thanks!
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