# Search the Community

Showing results for tags 'POP'.

• ### Search By Tags

Type tags separated by commas.

### Forums

• General
• Lounge/General chat
• Education
• Jobs
• Marketplace
• Houdini
• General Houdini Questions
• Effects
• Modeling
• Animation & Rigging
• Lighting & Rendering
• Compositing
• Games
• Tools (HDA's etc.)
• Coders Corner
• HDK : Houdini Development Kit
• Scripting
• Art and Challenges
• Finished Work
• Work in Progress
• VFX Challenge
• Effects Challenge Archive
• Systems and Other Applications
• Other 3d Packages
• Operating Systems
• Hardware
• Pipeline
• od|force
• Feedback, Suggestions, Bugs

• 0 Replies

• 0 Views

### Interests

Found 195 results

1. ## sticking particles to the animated emitting surface

I need to stick several million particles on their animated source geometry at the exact point where they are emitted from and follow the geometry's (emission point's) position. Please guide me towards any resource that might explain this process clearly. best regards
2. ## Particles along a curve - constraint Z orientation

Hi everyone, I'm trying to do a school of fish with a particle system that would follow a curve. Basically I'm emitting some particles and they move along a curve with a popcurveforce. By default the particles orientation seem to go along with the curve but since I'm trying to do a school of fish, I would like my particles Z orientation to always be 0 so the fishes don't swim on the back. So far I've tried with this expression in a popwrangle : p@orient.z = 0; The thing is it seems to zero out the orientation of x and y as well.. And I still want the x and y to go along with the curve. I'v tried with a popattract instead of a popcurveforce and I'm still not able to constraint the Z orient.. Maybe it has to do with something else than the @orient attribute since I don't see it in my geometry spreadsheet..? There's something I don't get! (Needless to say that I'm new in Houdini :P) Thanks a lot! test_fish_school.hiplc
3. ## Popnet Kill

Hello! I'm trying to kill points inside DOPs (well a popnet actually). The way I'd like to do this is by finding the closest point to the ground object (how do I reference an object in DOPs?) and computing the vector from the POP point to the nearest point, then dotting that onto the ground points normal vector. That's a nice way to figure out which side of the ground the point is on, then killing it. At least that works outside of DOPs. I'm wondering how I can do this inside DOPs because I don't want to post-process kill thousands of points if I can kill them in the simulation. Any ideas? Thanks, cw
4. ## Particles collide inside a mesh

Hello everyone,Sorry for the basic question but I just want to emit some bouncing balls inside a mesh with Houdini 15.5. To create that I just create a source particle emitter and I put it inside my collider mesh. I make the mesh a static object and increase the uniform division and click on invert sign in the static object node. But when I launch the simulation the particles have a very strange behavior. If anyone have some idea to achieve this.Thank you for your response. animation_particles_gpe_v003.hip
5. ## POP Fireworks - Color from Image

Hey guys, I have to create fireworks that turn into some specific shapes. Just like this: I have an workflow idea working with colors. It goes like this: -Simulate standard the fireworks; -Go to a specific frame where the where the starbusrt* is fully formed; -Apply the color at this specific frame; -keep that specific color assigned to individual particles through the whole simulation; (not working) does it make sense? I'm having problems to achieve this last step. what I'm doing is: -caching the simulation; -apply the colors; -add a timeshif to the "rest" frame (89 in this case); -copy the color attributes from this frame (89) to the animated simulation; I guess it happens because the particle count changes during the sim. Any idea on how to proceed? (Scene file is attached) Thank you, Alvaro *starburst is the round shape Fireworks.v1b.rar
6. ## Velocity from animated sequence / Optical Flow

Hello, I was wondering if it's possible to create velocity vectors from an animated sequence (texture). Ideally something similar to Optical Flow. I can extract movement from geometry (eg. use trail to generate v vector of animated VOP) and I can do basic image analysis (eg. convolution kernel operations on coloured points using VOP) so I feel it could be kind of possible to do it but can't get my head around it. In terms of results I'd like to create a particle system that reacts to an animated texture (eg. overlay particles on a animated texture and have them follow the movements in the video) thanks!
7. ## Use Points as Particles

Hi, Let's say I have a bunch of points that I have created, and I want to treat them as particles in a popnet - how do I do this? Is it possible to do this without emitting from the source points for one frame? I noticed that you can set the initial geometry for the popobject node, and gravity and forces do effect these points, but no pop nodes do anything at all. How do I get the pop solver to consider these points as particles? I have attached a simple example. (Note: The popsource node has the Geometry Source set to 'Use DOP Objects', but this is undocumented) Points_as_Particles.hipnc
8. ## Add Hard Constraint between two particles !

Hi does anyone know how can I add a hard constraint between two or more particles ? exactly like RBD objects but it should be work for POP solver. I prefer do this via custom VEX codes for manipulating P or V. Thanks S
9. ## Deforming geometry increases pyro sim time?

Hello, everyone A simple question, it's basically the title. By "increase" I mean increase by a lot. Everything the same, just turning on "Use deforming geometry" increases the sim from 60 frames in around 8 hours to 7 frames in the same time From what I could see it really takes a long time in the "creating collision mask" (or something of the sort) step. I have the VDB of the colliding object already cached in a SSD. So, is this normal? Also, a side-question, when you use a static object in DOPs, does it use the Bullet Solver or the RBD solver by default? I'm sure I saw this question here before, but unfortunately I can't find it
10. ## retarget or recompute vector

Hi everyone, I try to figure out how to retarget a vector (v in that case) in particle trails. I explain: i got master particles who trail other particles in space, i inherit the master "v" to achieve a motion blur at render time, to avoid to much substep that way i got smooth line at low calculation cost. but i need to slightly noise the trails to achieve a "moving tentacles" look. Here is the problem when i apply the noise, obviously my "fake" v vector is not aligned anymore, it's stepped... i tried to recompute the vector with the help of id, but since my emission is not constant ( i shot on frame 5, frame10, frame15 etc..)the incrementation of the id in not constant to...I tried basic vector arithmetic, but i don't get results i need...I join a hip file, does anyone got an idea??? thanks by advance. Best H PS:excuse my english, I'm French... RecomputVelTest.hip
11. ## Copy-POP problem

Hi, I create a new project but have a new problem. use to source object its has not problem but when added the point on source objects its changing rotation. I hope, you can help me for ı can fix my files.
12. ## particles on surface transition

Hello, I'm trying to control some particles, I need them to travel on a ground, toward an object, then creep up on that object surface, when they reach it. I've tried a few method (creep, ray, slide on collision ...) but even if I manage to have them slide on an object surface, my problem is how to set up the POP network in order to have them transitioning from one surface to another. I've cheated with a P.y = 0 in order to have them on the ground with ease, but I'm failing at controlling a nice transition from ground to object. here is a basic setup, without much, in order to not restrict the different approaches . Also, I'll replace the particle with a small disk later, so I think I need them (particles) to be oriented properly. Thanks for any advise and help! prtcl_slide_4OD.hipnc
13. ## How to affect density (alpha) of a pyro sim using particles' attribute "\$AGE"

Hi all, a question about doing vapor trails (contrails). I'm looking to do a contrail from an engine of a jet, and the method I'm using is 1. Do a pyro sim, and cache out a single frame. 2. With POP network, birth particle points with attribute \$AGE 3. Using copy SOP, copy the cached out single frame of the pyro smoke onto each point of the points from POP. 4. Create alpha attribute on the POP points using the expression I found searching on this forum on a point SOP, as answer provided by member Wolfwood; 1-smooth(\$AGE,2,3) Now this works well on the Points, as the points fade out to 0 alpha and disappear after 3 seconds, but since I'm copying the static single pyro sim a (.bgeo) on to each of these points, I want the volume to have the same behavior; that is, after 3 seconds, completely disappear. Of course, since I'm copying the volume onto points, when points die after certain number of seconds(say, 6 seconds), the volume that has been copied onto the point also dies, but it's not gradual, rather, it just dies suddenly without slow fade to zero alpha. So, the question is, what is the best way to transfer this slow fading of alpha attribute onto the volumes? I thought about using the expression on the material' density, but then the entire volume trail fades together, whereas I want the volume to start fading few seconds after they're born, that is, the volume furthest from the traveling jet's engine fades first. I hope this makes sense and I would appreciate any insight. Thanks!
14. ## collider SIlly question: deactivating a passive collider ?

Hello I need to deactivate a passive collider at some point in my sim, and I can't figure out a simple way to deactivate it. I've tried groups, affectors, 'active value'. It's probably a simple fix, but the only 'hack' that I've found is to use a merge under my static object (merge with a null) and keyframe its activation between 1 and 0 Thanks in advance Bernie
15. ## more sand/grain question

As nobody answered my previous post (no hard feelings ), here I am again. I have made some progress with sand/grain but I'm still not sure of the process. In this new file I'm trying to have the sand to gradually blow away . I'm using a PopForce to move my particles and I'm controlling the v@Force Attribute with a voppop. I'm using a ramp based on Y and a turbulence noise to set the @force value as I would like the sand to start blowing randomly from the top and slowly go down the pile of sand. But I have 2 problems. 1- because the noise and the ramp are based on position, the particles enter and exit the noise/value 2- the noise is fading to quickly, I think I need to add a fit node to compensate.. but I can't figure it out. Here is my ramp/noise test (on a volume). PS: my previous post was about sand disintegration. and I attached a Hip of my scene. Please Help me out! sandtest_forceRandom.hiplc
16. ## sand disintegration

Hello, I'm trying to get a logo to dissolve/disintegrate into sand. Like it is made out of sand and something is eating out the outside shell and the sand is pouring out. In the attached file I was first trying to use a geometry and use attribute transfer to set the force of a popforce. as I would like to use in the future a more random/noisy pattern. I'm not exactly sure if my expression is wrong, if my whole set up is wrong. I tried to look around for tutorials or thread but couldn't find any. Any idea, suggestion or links would be greatly appreciated. thanks bil Sand_Desintegration01.hipnc
17. ## Blowing grains from object

Hey, I'm trying to create blow effects for my particles which will be snow. At this moment I have smoke advect which drive my particles but it still looks really bad. I would like to create light snow/grains like a dust which will unhide object after blow. Fox example: ball is hidden under the small amount of snow and someone blow this snow using mouth to unhide this object which is under it. hope it is enough clear to understand what I mean. advec.hipnc
18. ## Pops following animated mesh

Hello everyone ! Does someone know how to use an animated mesh for driving some velocities of particles ? I have done a sim that I like but I want it to follow the character's animation... The particles born in the chest and goes to his head which is rotating... I'm pretty new to pops, I think that maybe I can make it move through a pcopen but maybe it is a bit too much for what I want to do ? Also, I'm not pretty sure about how to make it... Maybe it's possible to feed the pcopen with a scatter of point on the surface of the character ? Thanks a lot and have a great day ! (Once finished and online I will try to post it as a comment !)
19. ## Optimizing pop sim - set inactive?

Hello, I am dealing with a particle sim and I need some way of optimizing it. This is the case: particles are emitted and falling on the ground. Once they fall on the ground they bounce a bit and then stop moving. In this simulation I need to emit a lot of particles so it goes slow after a bit as particles accumulate fast on the ground. However I don't need to simulate those particles on the ground anymore, but pop solver simulates them all. Is there some sort of equivalent of @active attribute as in bullet sim? I can think of one way - I can set up a velocity treshold, which will move stopped particles to a group. Then I can remove particles from this group so that pop solver doesn't simulate them, but before that I will collect them in another solver? Any better approaches / ideas? Juraj
20. ## POP Group Center

Hey guys, Hopefully this is a quick one. I was wondering how I could find the average position of a group of particles (and store the position as an attribute on the particles in that group)? Say I have two groups, A and B, and I want to find the average position of the particles in group A and create a force on the particles in group B to go towards that point (center of A), and at the same time have all the particles in group A move towards center of B. POP Group A -> Center of POP Group B POP Group B -> Center of POP Group A Thanks
21. ## Grains to volume

Hey guys, First post so go easy! But I was wondering if there was a way to convert the wet sand POP grains I've made into a volume by creating the vdb from the points generated by the sand? I've had a look around but can't really seem to find anything on it. I attached my .hip, its pretty straight forward, but the idea was to get the sphere to slice in half, but then recreate the geometry from the volume. Thanks split.hip
22. ## Thread Unwinds Forming Shape?

Hi All, I am trying to implement a concept of a spool of thread that unwinds leaving a trail that then takes on the shape of the classic "support this cause" ribbon. I have started with Matt's Pop Trails example file and replaced the scatter with an Object Merge of a single point from an external object that tracks the spools Z position. This gets me a single thread trailing the spool. What I don't know how to do, is to make the trailing thread take on the proposed shape for the concept? Is this Pop Trails example the best way to handle this or is there a better approach? Thanks ap_me_pop_trails_spool_thread.hipnc
23. ## Creating a Realistic Gun Impact System

Hello Everyone, I am rookie in houdini and currently i`m struggling in making a gun impact system in houdini, which should have a characteristic to make dents according to the properties where the bullets like metal, concrete wall, brickwall, wood etc. Please help me. A help with a hip file will be nice and helpful more to me