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Found 24 results

  1. Hi there, I have been fighting with this for a while. I want to fill a geometry with a flip fluid but the geometry is watertight. the fluid is a stream comming from outside and colliding on the inside and filling up the geometry. one would think that inversed normals could do the trick but it doesnt seem to work that way. the other solution would be to disable collisions before the particles are inside the object. but i could not figure out how to disable the collisions per particle before they enter the volume. it seems like a very common problem but i could not find a straight answer anywhere. any suggestions? thanks
  2. Smoke interaction

    I would like to make 2 smoke sources to interact with each other. How can I set up my scene to make it happen? smoke.hipnc
  3. Random pop bounce direction

    Hi, I'm trying to achieve a simple effect, but am struggling to get my head around it. I'm sure I'm overthinking it but if anyone could help me that would be great! I'm trying to get a random bounce direction on particles when the collide with the ground plane. As if the particles were small stones bouncing randomly due to a bumpy road surface. I've attached a hip file with the basic setup. I was thinking maybe you could inherit a random vector as the collision happens, but couldn't seem to figure a way to do it. I know various sources have mentioned the old "gain normal" parameter, but this no longer exists. Any help would be much appreciated. odforce_randompopdirection.hip
  4. Hi people, I got some problem with color loss in my balls array attached to point box. Everything is working as intended until I transform my array to RBD Object. In my scene I would like to have balls bounce around and collide with everything but I would like to have some materials and distribute them randomly on them as well. Everything is working but color is lost inside Assemble node at the end in Attribute Wrangle node called : add_name_attribute. I have no idea what happens but this node is making additional groups from my balls and in the end there are many groups which I don't need. All balls are turning grey in viewport as well. If you could have a look I would be grateful. ajz3d_randomize_materials2.hipnc
  5. FLIP Collision and behaviours

    Hello, I come from a Realflow background where you adjust the collision settings like roughness and bounce within the menus of the object of collision. In houdini there are 2 places where I see the same settings, and I don't know if both of them affect the simulation (if not, then wich one?): FLIP Object -> Properties -> Physical. Static Object -> Physical. In Realflow there was a parameter that easily let me escalate the intensity of the collisions, meaning that some objects would create bigger disturbance and higher splashes (not affecting the global forces on the scene). In Houdini I thought the equivalent was Velocity Scale on collisions, and I tried to change the value to 0 only to find out that not much changed in the splashes generated by the collisions... Any idea how to achieve this difference in intensity? Thanks
  6. FLIP Spray not colliding

    Hello every one, I am doing a regular FLIP simulation where I have my particles colliding properly with a passive object. I have added a whitewater dopnetwork from shelf, and I re-created the collision setup in there. When I add foam and spray, everything goes as expected, but the spray just goes ballistic and completly ignores th collision borders. In the capture below you have an example of the overshooting particles (the ones making the correct form are the regular corefluid FLIP particles).
  7. Particle movement and collisions?

    Hey guys! I'm trying to make some floating particles inside a geometry. I need the geo to be a collision object and the particles to kinda have a buffer area before they touch anything, not very obvious but enough so nothing actually collides. However, I'm having trouble getting the particles to actually treat the geo as a collision object, and also stopping some of the random ones that like to go super fast. I thought that the popspeedlimit would the trick for the fast ones, however, it kinda clamps the whole speed of all the particles, rather than clamping the velocity of the fast ones. Anyway, here is the scene file with the alembic, if anyone has an idea of how to fix this please let me know! underwater_particles.009.hipnc blockoutForSim.abc
  8. Pyro Collisions

    Hi, I am dealing with some pyro collision problems. I have an explosion that is penetrating the roof collision shape. Part of the trouble is that the collision is fairly thin and the pyro sim is moving fast. I can make the collisions perfect by setting the substeps to a ridiculously high number, such as 10. What is a better way to deal with my problem other than high substeps? As you can see, most of the fire is colliding, but some seems to seep through. Thanks
  9. Pyro collision velocity leak

    Hello guys, maybe anyone knows why on pyro collisions, velocity still leaks? Density works properly, but not velocity. Maybe there is some simple checkbox or it's by design and I should delete those velocities by some advanced hacks? Any ideas? Thank you! collision_pyro.hip
  10. Dealing with FEM + Static Body

    Good night, people: I'm a newbie with Houdini. I've tried lots of tutorials but, I'm still having problems with collisions. I made a simple setup, a growing fem ball inside a static collider, but, it interpenetrates the walls of the static object. I tried to get more substeps, to have more detail in collision guides, but I'm not sure what I'm doing wrong. I attach the file that I'm working on. Thanks! testme.hipnc
  11. Partial collision detection

    hey, little problem here. I have a piece of cloth made out of grains. Its colliding with an object. Here I use a collision detection in combination with a collision behaviour. The collision detection shall only detect a few polygons of the whole object to stop the motion there. Referencint the polys in dops. Its giving me a correct collision guide but during the sim it keeps ignoring it. Insteat it freezes the grains along the whole 'main collision object'. So that are the areas to collide with, just a few squares.
  12. Hair Collisions

    Hi guys, I have a hair sim that im trying to do, i've got everything setup and working with the exception of collisions with other objects. The hair will collide with the skin surface, but im trying to add collisions with his clothing. I've created an external dopnet and merged in a static object (his coat). I've verified that the collision guide is accurate but i can't get it to collide with the hair wire object. Collide Independent and Collide Codependent are enabled on the wire object. Any help would be gratefully appreciated Thanks
  13. Sporadic Particle Motion Blur

    Houdini FX 15.0.313 Im working towards creating a stream of particles that hits two characters in the scene, mimicking water from a small hose at high pressure. Everything looks great in the view port but when I render the motion blur is sporadic and showing up as if the particles have very jittery motion when all they should be doing is travelling in one general direction. I tried using a trail node to generate velocity data but it doesnt seem to fix the issue. Any ideas as to what is causing this? Any way to get around it? waterSpray.hip
  14. Hi, Im working on a desert scene with a dust cloud blowing over some nice sand dunes geo. No matter what I do the pyro keeps clipping straight through the geo. The weird thing is this did happen with particles. Heres some of the things I've tried: Selecting the geo and making it a Static Object, Selecting the geo and making it a Terrain Object, Ticking the Use Deforming Geometry box, Ticking the Create Active Object box, Unticking the 'Use Volume Based Collision Detection' in the Collisions/RBD Solver tab. Changing Offset Surface from 0 to 1, 2 or 3. Im guessing there are some nodes that I will need to work with and connect up in order to produce a better collision but I do not know where to start. Any help appreciated, Thankyou Charlie
  15. Chain Links?

    Hello, I've been trying to create wrecking ball that I can use to smash into a brick wall. I made one using torus' and a big sphere. However, when I try to simulate it as an RBD packed object in a dopnet they just fall through eachother. Sometimes one will hold for a few seconds but it just falls afterwards. Does anyone have any advice? The objects are blue because collision geometry is on.
  16. Hi, folks. I need to set up a simulation where dynamically-generated arrows fly, then collide with a deforming surface and stay stuck to that surface (shields carried by moving soldiers). Importantly, the arrows should NOT just align along the prim normal on collision; they should protrude at the angle at which they collided. This is a topic that's come up before, but I haven't been able to find a satisfactory answer about it. Some suggestions don't quite hit all the elements I need; some are for older versions of Houdini and so might not be as relevant/accurate (I'm on H14). The approaches I've considered are: 1. Particle-based arrows that stick. It's easy enough to copy arrow geo onto a particle sim, and have the particles stick to the collisions surface. However, then the particles have to start inheriting the orientation of the collision prim as it continues to move. This could be handled two ways: The collision geo is deforming. In this case I'll somehow have to calculate how the collision prim has transformed from the moment of impact to the current time. The collision geo is transforming. In this case I'd use rivets to attach non-deforming stand-in geo to the moving collision objects (which don't change shape). Not ideal, but it might make it easier to work with the orientation values? 2. Particle-based arrows that create geo. Having already grown sick of the mathematical jungle of quaternions, matrices, and dihedrals, I wondered if a better approach might be to make each particle spawn some geo in the colliding object's network instead (presumably using a SOP Solver?) , then die. This would hopefully eliminate the need to continuously update orientation. 3. RBD-based arrows with constraints. Moving away from particles altogether, I wondered about using simple Bullet geo for the arrows, and dynamically creating constraints to pin them to the shields when they impact. An advantage of this method would be that it would allow realistic stick-like collisions and bounces for loose arrows--something particles can't really do. If anyone has any thoughts about which of these methods is most promising, or has any specific advice about how to implement them, I'd be extremely grateful to hear. Thanks in advance!
  17. Matte/Alpha rendering

    Hi, For a school project I have made a FLIP sim that enters the scene when a door opens. The project has been 3Dcamera tracked, matchmoved and model-built to sit in the shot nicely. I am wondering what the pathway would be to render only the visible sim once the door has opened to let the fluid enter the scene. Would there be a material I can put on the door which will act as an alpha that I can use the original plate and as the door opens it is only the exposed sim that renders? I don't know how to set this up, haven't done many complex renders at all. I hope someone can help or at least point me in the right direction. Because my working file has a lot of imported objects I have just uploaded a still frame, hope that's okay
  18. Weird FLIP collisions

    Been trying to get a flip vdb collisions pipeline setup but i can`t get the velocity to simulate right . flip.hip
  19. Hi all! I'm trying to do a PBD sim of a character who's body turns into sand over time. My problem is that I'd like the sand as it falls to collide with the moving body but obviously the parts of his body that have turned into sand should no longer be collided with as they are no longer there. This poses a big problem that I have not found a solution for. How do you have a collision object that's topology is changing over time? Houdini cannot interpolate between frames where the point count/order changes which makes complete sense but what is the alternative? Can anyone offer a solution or alternative approach for me? In the attached file you can see the spread (in red) where the character is turning into sand. The parts that are not red need to remain as collisions. Thanks so much!
  20. FlipTank EMPTY itself *Problem*

    Hi, I've been doing a boat like effect, started from FlipTank (from shelf) but as I add to Flip Solver (in Volume Velocity input) a "Source_Collision_from_Volume" that is my volume made from PolyfromVDB attatch to a Fluid Source that is used to create my "collisionVelocity" attribute the Tank get EMPTY after a couple frame. Thanks
  21. The collisions between the flip source and static object is completely ignored, what am i doing wrong. I have attached the .hip and a bgeo. Please help ! SandPit.zip
  22. Hey all, I am very new to Houdini and am trying to use the wire object/wire solver to simulate fur on a tiger. I have it setup and working, but when I increase the number of curves I'm simulating, I get some issues. Mainly, some of the wires get caught inside the tiger geometry and look like they get stuck and therefore stretch. It seems to be when the tiger's legs come very close together, the wires from one leg get stuck inside the other. Does anyone have any experience on how to resolve this? I am using volume based collisions on a static object and static solver, and the settings are pretty much the default settings. Any help would be greatly appreciated. Thanks.
  23. Hello everzone! I'd like to ask if there's a way to increase the splashes from collision (made by static RBD object) objects.. I have a setup which works (more or less :-) ) and I need the water to be traveling at this speed. But I'd like it to be splashing on the rocks and be more wild on the collisions. Is there a way to increase the collision effect/add more splash particles on collision? I tried to play with the whitewater emitter settings (min/max curvature, speed, etc..), but it doesn't work.. Thanks for any advice! splash_tank_test.hip
  24. multiply collision with density

    Hi everyone I'm using a smoke simulation where a simple source is dripping smoke on a collision box. The collision uses the sourcevolume method, so I have the SDF collision available. I'd like to create an additional field which is nothing else than the result between the multiplication (intersection) between the collision field (after gassdftofog) and the density field. Basically I'd like to use this resulting field into a pyro symulation (a separated sim) as fuel to emit fire. The result would be that some fire emits from the locations of the cube where the smoke is dripping. I used a match field to fill a field "collisioncopy" scalar field, and filling it with the content of the collision sdf after converting it to fog. Then I used a gaslinearcombination with the folliwing calculation collisioncopy=collisioncopy*density The problem i have is that obviously the collision field and the density field are mutually excusive so the result is an empty field. My question is: is there some quick and dirty way to "expand" a certain field by a certain amount of voxels (in the direction of the gradient of its density for instance). This way i would be able to have an overlapping area between my collision field and the density and I could calculate the intersection between them.