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Found 217 results

  1. Hi. I have a setup with boxes scattered in a circle position. Inside rbdbulletsolver i try to use LookAt in order to force boxes always face the center while they move around. But fo some reason look at rotates all boxes. I know there must ne something with up vector but cant fiure out by myself. I tried to different options within look at and tried to assign different up values but still cant figure out how to make look at force objects to actually look in the center of coordinates without weird rotation. Please... help The file is attached. untitled.hip
  2. Hello I'm trying to turn a pop wind object on/off. I first tried to just keyframe it, but then I get smooth values between 0 and 1 and all i want is on and off. I then noticed there is a handy 'use VEXpressions' box in there. but I do not know how to access 'Activation'. The editor does not like Activate, Active, Activation, with or without an @ Symbol. The SideFX help pages seem to indicate this is possible, but without showing how to do it. https://www.sidefx.com/docs/houdini/nodes/dop/popwind.html#parameters This is what I tired: if(@Frame == 1 || 20) { @Activate = 1; } if(@Frame == 10 || 30) { @Activate = 0; }
  3. Vellum/POP Grains sim limitation

    Hey everyone ! I would need your help on a sand simulation that I'm working on. It's a 10m high building which is supposed to crumble as a sand castle. My first thought was to try to do it with vellum grains, but the issue is that I'm getting limited by the amount of particles that I can have. Indeed, my GPU gets full and I've got the classic Kernel issue error in the console, meaning I just can't simulate my thing. I've tried to disable every OpenCL buttons that I could find on the solver (OpenCL Graph Coloring & OpenCL Neighbor Search) thinking it would just disable the use of the GPU for the sim, eventhough I knew it would make it really slow (at least it would have been computed). But it didn't work. Then I tried to use POP Grains cause from what I've understood, it's not using any GPU accelerated system. But I've got the same issue, the sim just can't be cooked. Would you have any suggestion for me ? I'm running this on a Threadripper 3960x and a RTX 3080. test_10.mp4
  4. Hi everyone, I created simple pop network with fixed particle count (100) and connect sphere to particle points. I want to export 100 animated seperated spheres to fbx files. I try to different ways but spheres not moving in fbx files Waiting for gold helps thanks.
  5. Dear all, Plz give me some suggestions to do simulation of talcum powder as I shown in attached reference gif. Thanks in advance..
  6. OpenCL for pop?

    Is there an existing workflow to run a pop sim on the gpu?
  7. Hi, I'm getting some very weird behaviour with some of my particles that collide with my VDB. They should come to rest but a small percentage don't ever stop moving. The collider is a VDB created using the Collision Source node and represents the original RBD pieces converted to a volume. I've tried using Auto Sleep and various other methods but these same particles just never stop. In one of the videos the purple colour is the active particles and the red are the sleeping particles. I've upped the substeps in the pop solver to 20 and they sill move. Any advice would be much appreciated. POPNeverStopsFlipbook.mp4 POPNeverStops.mp4
  8. Hi My first post in the forum! I have a particle stream and I'd like to use the particles to instance vellum objects. I have this working, almost.. The problem is that the Vellum Source creates a continuous stream for each particle, in other words, Particle Id0 has one object on frame one, two on frame two, etc. The setup works if I give each particle one frame lifespan, but in my scene I want the vellum to stay attached to the particle as it moves. Should I create 2 pop sources and with the first, have 1 frame life span and create the vellum objects, then use the other pop source as a constraint or attach to geo to keep the vellum constrained to the particles as they move? I only want one vellum object instanced on each particle, can anyone please offer any tips on how to achieve this? Thank you! VellumOnPOP_01.hiplc
  9. I have a 1 object that consists of a ~1000 closed curves/splines (same ammount of primitives), i want to generate particles on each curve and move those particles along them, but each particle stays on that same curve it has been generated onto. i started with popnet with a force and a pop wrangle @P = minpos(1,@P); but of course the particles are jumping on the next spline when it comes near it, which i want to avoid. Also tried adding the popnet inside a for each prim loop, but not sure how to use metadata from that loop inside a popnet (particles disappear after the 1st frame) Can any1 please guide me on what logic i should be using?
  10. Smoke As Points?

    Is there a way to visualize billowy smoke as a volume of points? I'm working with a simulation where I'm passing objects through a volume to see how they create air currents. I've been able to BS it up to this point using a pop network and applying a pop curveforce following the path of the objects, but it clearly isn't the objects interacting with the volume and the movement is very uniform. In the picture I attached, you can see the curve force pushing the points, but obviously it isn't the object generating any change in the volume. I've got a simple billowy smoke volume set up in another file with an object that successfully collides with the smoke and pushes it around. So basically I'm trying to visualize the billowy smoke but as a volume of points like what I already have. I'm sure its a relatively simple operation but I've googled "visualize smoke as points" in every way I can imagine and haven't found it. Thanks so much
  11. I'm working on a POP simulation for a rainy window and I've set up the simulation so that source particles (in yellow) fall with erratic motion due to a varying POP Wind force and Gravity force, emitting a stream of particles behind them (in green) as they fall using POP replicate. The emitted particles are stopped immediately after emission (using the stopped attribute in a POP wrangle). The issue is that as soon as the POP replicate is activated (at frame 200 in the video), the erratic motion of the source particles is lost and they travel more slowly in straight diagonal lines (as the trails of the emitted particles show). I believe that the POP interact node is causing this as the source particles are being attracted to the stationary emitted particles, slowing them down. But what I don't understand is that the POP interact and replicate are in separate particle streams so the emitted particles shouldn't have any effect on the source particles. I've attached a hip file along with a video illustrating the change in motion when POP Replicate is activated. Any help would be much appreciated as I'm pretty stuck on this! Thanks Houdini_POP_Replicate_Question.mp4 POP Replicate Issue.hip
  12. Hey everyone! This is my first post here! I have a scene where I'm caching a vellum grains simulation to a disk cache. I'm having trouble understanding why it takes so long. When I cache the simulation to ram in the viewport each frame takes about 15 seconds, however when I drop a File Cache SOP and save it to my hard drive each frame seems to take about 3 minutes. Could someone explain why this may be? I have tried saving to another drive and it didn't help.
  13. I'm currently working on a POP netowork to simulate raindrops on a window, and am trying to isolate the original particles from which the trails (in red) are emitted as per an emit attribute using the POP replicate node, so that I can selecting apply a POP interact force to them. However, I'm really struggling to find a way to isolate those points. I couldnt find any reference to the original points within the POP replicate node, apart from the fact that their ID is added to the sourceptnum attribute. Am I missing an obvious solution? Thanks
  14. Instance node loses UVs

    I have an animated alembic loop that I am copying to points from a POPnet, but I want each copy to be slightly randomly offset time-wise. I would love to be able to do this with my original alembic (I'll be posting this question separately), but the only method I've found is Tim van Helsdingen's method that explicitly calls the cached frames, just adds an offset to the $F part of the path, and then uses the instance node to do the instancing, so I'm doing that having recached my .abc as a .bgeo sequence. The problem is that the instance node doesn't retrieve the UVs for the objects, and I haven't been able to find a way to get them to carry through. How can I get the UVs to be seen in the instanced objects? [ADDENDUM: I figured out how to do it using a for-loop for all of the emitted points, copying an instance of the .abc going through a time shift that randomized a frame offset based on the iteration count of the loop. This works, but is also considerably slower for the merely-300 objects I'm instancing, so any alternate-method suggestions are definitely welcome!]
  15. Hi all. This should be easy, but it's killing me... I have a control object living outside a DOP network, a simple particle system. I've plugged it into the second input. Inside the DOP I access this control position without issue, in a VOP. However I then want to follow up by killing particles in a POP wrangle, based on distance to the control object... Easy right? Here's my vex: f@dist = distance(@P, v@opinput0_P); if ( @dist <= ch("threshold")) { removepoint(0,@ptnum);} ... simple. But it kills particles around the origin, not the control object, as if v@opinput0_P = {0,0,0} I've tried multiple variants on opinput, explicit path and the point function etc but it always gives me a "kill" radius around the origin, not the control object. Anyone see what I'm missing? Thanks in advance!
  16. Houdini.School Velocity Forces

    I am happy to announce that https://www.houdini.school has launched and you can get 15% off now through July 27th, 2021. I'll be joining a host of talented Houdini teachers, like: Debra Isaac Kate Xagoraris Beck Selmes Christopher Rutledge Justin Dykhouse Jeffy Mathew Philip Nicholas Ralabate You can learn more about my Velocity Forces class here: https://bit.ly/houdinivelocityforces Teaser video for my Velocity Forces live class: https://vimeo.com/577928177
  17. Hello! This is my first time posting here. I am a graduate student currently working on a project that involves a character comprised of rigid objects that can assemble, disassemble, and rearrange itself. The parts can also blend between dynamic and keyframed states. I have a method for the state switching, but I cannot seem to find away to apply any attractive or guiding forces to the parts when they are in their dynamic state. I found a way to do this previously by using a POP Attract node, but it only worked with Rigid Body Solver. I'm not sure how to apply that same node to a RBD Solver. If any knows how to make that work or knows a better method, I'd appreciate it. The goal in this test is to make the ball roll towards the cube and fit into one of the sockets. I have attached a zip file with the assets and .hip file. Thanks in advanced! RBDTesting.zip
  18. Flickering Liquid

    Hi there! I have this melting setup with a POP solver, basically scattering some points onto the original mesh and then melting then and meshing back everything again using "particlefluidsurface". So I have been trying to get rid of this flickering on the mesh, I have over 500k points and I also tried increasing the samples and playing with the particle separation in the "particlefluidsurface" I also tried using "vdbfromparticles" but its more or less the same result. I want to know if there is anything I can do to help reduce the flickering? Any help on this is much appreciated Thanks in advance untitled10.mp4
  19. I am trying to get donut sprinkle fx. like someone is dropping sprinkles to the donut for toppings. but i am not able to get it right. attached hip file is a basic POP sim setup, part i need help is when the particle stick to the geo/collider/donut the sprinkles are standing up. what i want is to randomly placed or stick on the geo. like the pic. POP_Sprinkle_Odforce1.hiplc
  20. Mulitple Pop source emitters

    i have around 100 points that are emitting particles. each source point in SOPs has an attribute i would like to use in DOPs to activate or deactivate the birth of particles. i cant use it directly in impulse activation unfortunately How can i do this?
  21. Rbd objects emit particles

    i have some cubes that fall to the ground. I am trying to emit particles at the same time from the front side of each cube creating noodles that collide with the cubes. i thought the multisolver might come in handy but its not working so far. First time i am using it. Essentially i am trying to replicate grain emitted noodles on cgwiki https://www.tokeru.com/cgwiki/index.php?title=HoudiniDops#Grain_emitted_noodles but my source is an rbd object. i am not sure if this is possible. test.hip
  22. POP proximity to group

    Hi everyone! I have a very basic POP setup. The side with positive P.x belongs to group "right". With a "POP proximity" node I check nearest particle. My goal is to fins if particles from "left" have a nearest neighbour from group "right" and if they have color them red. In my opinion it should be simple. The nearest attribute gives you a number of a nearest point and you use it within "inpointgroup" to check if nearest belongs to this group. If it belongs color red the point that has a current nearest as its attribute.... But it doesn't work. I tried to put the same code in in a "geowrangle" but it wasn't working also there. (in general what's the difference between "popwrangle" and "geowrangle"???). I trief to solve the problem avoiding "inpointgroup" by assigning the attribute ntest to particles from the right and checking in popwrangle within "point(0,"ntest",npt)" if a nearest has the ntest attribute equal 1... but again things aren't working... Apparently "point" doesn't work that way in POPs or I use ot wrong... don't know..
  23. pop fluid along curve problems

    Hi all, I have pop fluid running along a curve. All great at the start but when it gets near the end of the curve, the fluid floats away, gets a little messy. Any advice on keeping the particles on the curve? hip file attached. waterSpiral.v011.hip flipbook_waterSpiral_v10_waterSpiral_v10.mov
  24. POP stream/group in wrangle

    Hi everyone. I have a pop stream called "stream_main" and is written that its a pointgroup. Though when I refer to it in a wrangle, if doesn't work. I don't know why.
  25. POP Force Mass Remap

    Hello Everyone I noticed that many parameters have a "Use VEXpressions" checkbox and i try to understand them. In my example i would like to remap the mass of the pieces by VEX. Preferably using a Ramp! And all that inside the local VEX of the POP Force :-) So that there is a better distribution of pieces in Y. I can't make it work... should it?
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