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Andy Nicholas

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About Andy Nicholas

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    Soho, London

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  1. RBDs and Field Forces

    Hi Bryan, I'm not going to be in front of Houdini for a few days, so I'll have to get back to then. Cheers! Andy
  2. Adding Custom Agent To Crowds?

    Duh. Okay, just figured it out. At the top of each layer file is this: { "version":1, "name":"default", "static":[ { ... You need to change the "name" entry to the same name as the layer file. Would've been good if Houdini could be a little more helpful with an error message when the layer suffix in the filename doesn't match the JSON entry! Thanks for the help Cameron. Guess I just need some specs A
  3. Adding Custom Agent To Crowds?

    Yep, that's how it's set up by default when you use the Bake Agent shelf tool. I'm sceptical, have you tried it? The drop down menu's for the shape layer overrides don't populate if you plug it an at that stage. They only seem to work when you plug them into an Agent SOP. But I'll have a play around and see what I can figure out.
  4. Adding Custom Agent To Crowds?

    HI Cameron, Yep, I agree! It's hard to debug with what I've shown, I was just hoping someone had encountered this already. My impression was that the Agent Layer SOP is intended to be used after the agent has been cached to disk? I.e. to modify the incoming agent for render that's already been cached, rather than being used to generate layers which are then cached out. That's been my assumption up to now as I'm not sure where you'd put it if it's supposed to be used before caching. Will look into it. The other issue with the Agent Layer SOP is that while it appears to be set up to support rigid meshes, but doesn't appear to have anything to allow you to add layers of deformable geometry. I'm still finding my way through all of this, so maybe I've just missed something? Anyway, I'll look at putting together a simple scene together to upload as an example. I've had a few thoughts since my original post that I'm gonna test out first, but either way, I'll post back here tomorrow. Thanks for your help. Andy
  5. Adding Custom Agent To Crowds?

    Hi guys, Just wondering if you got anywhere with the layer manipulation? I'm trying to do something similar where I have 4 different deforming meshes. I've baked the agent with all the geometry inside, and then created extra layer files to support each piece of geometry. E.g. for the layer where the agent is wearing a jersey, I have ./myagent_layer.jersey.lay "deforming":[ { "transform":"geo_Jersey", "shape":"jersey.geo_Jersey", "bounds_scale":1 } ] I've also modified the shapelip Bgeo to make sure the name attribute on the primitive matches (i.e. jersey.geo_Jersey). When I go in to the Agent SOP and change the current layer to jersey, I don't see any geometry at all. Is that normal? I can see geometry for the default and collision layers, but not for the custom ones. Any ideas what's going on? Many thanks, Andy
  6. RBDs and Field Forces

    I don't know, I've not tried playing with it yet. It's on my list!
  7. RBDs and Field Forces

    Hey Ciaran! Thing is, it's not too hard to implement proper field evaluation for Bullet RBDs, so I'm frustrated that it's not supported out of the box. Frustrations are compounded by the fact that there's no obvious information in the documentation about what is supposed to work with what and zero UI feedback about when you're changing a parameter and it isn't working. The whole thing feels unfinished to me. It's like trying to play with someone else's half finished set up. It seems the only way is to reverse engineer DOPs to understand what's going on, and that p***** me off when I'm in a hurry! I guess I just expect better.
  8. RBDs and Field Forces

    Hi Petr, After a bit of playing around with the POP Spin By Volume, as an act of desperation I plugged the POP Solver into the Pre-Solve input of the RigidBody solver to see what would happen and it actually worked! Well... to a point. What the POP Spin By Volume seems to be doing is analysing the gradient of the volume field at the center of gravity to deduce a torque. So it's going to miss all the local variation of the field over the surface. Not a bad approximation though, and definitely a useful node for particles. Will dig into it to see what it's doing to the DOP objects. After playing around with all of this, what I'm finding frustrating is the fact that the fractured RBDs are implemented in a different way to regular RBDs. That means that any DOP otls you write have to support both ways of managing the data - none of which is particularly well documented. I'm keeping my fingers crossed that at some point they'll unify a lot of this to make it play together nicer! BTW if you or anyone reading this has a good "go to" source of information for getting into the guts of DOPs, then please post here! Thanks again for your help. A
  9. RBDs and Field Forces

    Hi Petr, Okay, that's worth investigating further. Thanks for the suggestion. It's worth mentioning that with some further work, I did manage to get a regular bullet RBD to be affected by the Field Force in a physically correct way. Basically I pulled in the geometry into a SOP network and looped over all the points, summing up the force and torque experienced by the object at that point in the field. I then used an expression to apply the total force and torque vectors using a Uniform Force DOP. It works well, but the method breaks down when you try and use something like a Fracture RBD object because I've not yet found a way to apply force and torque data to each individual RBD point. Maybe I can just apply it as an attribute, I don't know. The expectations of the DOP solvers on the incoming data is all really poorly documented - it's so frustrating! Just need to do more testing and experimentation. Cheers, A
  10. RBDs and Field Forces

    Aaah! Okay, thanks for that Pezetko. So seeing that the majority of the work I do uses the Bullet solver, is there a way to get this to work in that? If not, I'll use the opportunity to see if I can implement it myself. Cheers, Andy
  11. RBDs and Field Forces

    Hi all, Hopefully a simple question... how can a single RBD object get affected by a Field Force in such a way so that it spins? See attached hip file for the following discussion... I've set up a vector volume with vectors that push in the +ve x direction in the lower half of the box, and in the -ve x direction in the upper half. I've used this volume to create a Field Force. In the middle of that, I've placed a single RBD box. There's no gravity or ground plane. When I simulate, as far as I can tell, the rigid body only samples the Field Force at its center of gravity as it just starts to drift in position slightly. I would have expected the box to rotate a lot! I have a few questions: Is there a way of getting the RBD box to add up contributions across its surface to respond correctly to the field force? I should be developing a lot of torque on the box from this field. I tried playing with the Sampling parameter. Switching between Point, Circle, and Sphere, but they don't make a difference. How is this parameter supposed to be used? The Field Force node seems to respond to any SOP Vector Field I plug into it without worrying about the name of the volume I create in SOPs. So what's the purpose of the "Force Attribute" and "Torque Attribute" name parameters? How can I add torque? Think that about covers it. Thanks for any help you can give Ta! Andy field_force_test.hip
  12. Using impact data for wheel contact friction forces

    Hi Andrew, Thanks for taking a look. Much appreciated. It's bizarre, I had about 10 minutes yesterday when it worked, and then it went and broke again and it's not worked since. Crazy! I suspect it must be a bug so I'm going to have to see if there's another way. I'll try simplifying the setup and see at what point it breaks. Thanks again. I'll post back here if I figure it out. Cheers, Andy
  13. Using impact data for wheel contact friction forces

    Maybe I should simplify the question. Basically, I can't get the "op:" syntax to work for the VOP Force DOP. Can anyone else? If you want to test it, put a "Point Count" node down inside the VOP Force DOP, plug it into a print node, and try to read the number of points from a SOP in Houdini. It won't work for me. If I save geometry out, I can read it in with a file path. But no luck with the "op:" syntax. Might be a bug, but it'd be great if someone else can confirm. Thanks, A
  14. Hi guys, Does anyone have a way of iterating through impact data inside a VOP Force DOP? I've created a bunch of points in SOPs that is pulled from an ImpactAnalysis node, and I need to access it from a VOP Force DOP. I've tried pulling the points into the VOP Force as a pointcloud, and I've tried using the GetAttribute node too, but they don't work with the "op:/obj/myimpactpoints" syntax. (Is it me or is that syntax pretty flaky? It's an endless source of frustration for me!) What I'm trying to do is use the impact data to generate some custom frictional ground forces for a wheel. I can calculate the forces easily enough and apply them in the VOP force, as long as I can get the impact data in, but I can't get it in there. Is it possible to apply forces and torques in a SOP Solver instead? Suggestions welcomed! Thanks, Andy
  15. CmiVFX down again...

    Okay, so that's my point. If there's no difference between the two, why penalize your legitimate customers with forcing online viewing?