# All Activity

1. Today
2. ## Couple Vellum questions (pressure by att. and attach)

Hey for the first part of your question I can suggest this video. He shows how to create and attribute to drive the pressure. You have to create a sop solver in the vellum solver to transfer the attributes. For the second part you just need to create groups on the body and arms and use the vellum constraints like attach to geometry and then you can use your groups in there.
3. ## How to add color gradient through velocity plus collision to influence color velocity?

maybe it Helps ...again sorry can't open your file I use 16.5 H vel.hipnc
4. ## Change HDA UI Button color with Python

Hey, is there a way to change the color of Parameter Buttons in Houdini with python? Is "tkinter" working in houdini python? Thank you!
5. ## Instance random keyframe/animation with Python

Good morning, since I deeply fall in love with python, I would like to know where it makes sense to use Python or better VEX. I have a cube, that has on each frame from 1-10 a random rotation keyframed. Now I would like to copy/scatter these cube as a instance on a grid, but of course each cube should use a random animation of that 10 keyframes. Does that make sense in Python? And how would I start or what do I have to look for? I also would like to specify that I only use a range of keyframes. Lets say frames 1-5 have only rotation in x, frames 6-10 have rotation on y. My first thougts are: def pose_1_5_x(): keyframes_x = hou.parmTuple('/obj/box_object1/box1/r') for frame in range(1, keyframes_x 1): frames = (get all keyframes) retime = frames (set all keyframes to frame 1) etc etc etc ^^ But I guess, thats total bullshit I know, probably its more easy doing that in VEX or with for each - but would like to understand how to do that with Python. Thanks alot!
6. ## Vellum Cloth Collision

Hey, Noobini, no need to be rude. Here is the file. Freezed the draped cloth so no need to drape them again. Your case doesn't have RBD fractured object as a collision. I did it on purpose, so, as i said, by using the fractured object i can transfer the transformation, so no need to use deforming object. test_lag_ClothRack_v1.hipnc
7. ## 2D shapes boolean issue...

div, remove share edges ?.
8. ## 2D shapes boolean issue...

Hi; I tried to use boolean SOP on some 2D shapes, but the resulting geometry is not that clean. How can I get a clean result without unnecessary polygons? Thanks. Boolean2D.hip

Thank you.
10. ## Vellum Cloth Collision

just works... i still don't get ppl's attitude to wanting help but don't want to upload their files...f'kin annoying. vu_shirt.hiplc
11. ## Vellum Cloth Collision

Hi everybody. I have a cloth rack with hangers and clothes on it. The rack moves along the path. I simulated and cached the hangers moving with the rack. Then I modeled and draped the clothes on a static hanger and copied the draped clothes to each hanger to simulate the clothes on the moving hangers. I thought instead of using static deformed object it is better to use RBD fractured object (making it inactive) with point position, translating the transform of the hangers, so it would not load the collision geometry every frame. To help the vellum follow the animation of the hangers I also soft pinned with match animation those parts of clothes that "touch" the hangers. The problem is, after a couple of frames, the clothes start to penetrate the hangers. Increasing the substeps (tested with 10 and 20 substeps), collision passes, polish, post collision passes doesn't solve the problem. So generally I have 2 questions, first is: which collision type is used in vellum simulations: Bullet or Volume? And second: any thoughts on how can i solve my problem? Loading hangers through static deformed objects also dramatically increases calculation time.. Or is it the only option for vellum? Thanks in advance!
12. ## VDB combine intersection/difference not working cleanly

If you increase the bandwidth of your sphere VDB it works, set it to 3. [Exterior Band Voxels that is]

14. ## "Join SOP" issue...

Hi; I tried to connect some curves using "Join SOP", but the result is odd! How can I fix this? Thanks. Join.hip
15. ## How can I use an attribute to modify the "Rest Length(scale)" of vellum?

Thank you, Tomas.
16. ## How to add color gradient through velocity plus collision to influence color velocity?

Thank you for finding only "v@v" and trying to do it, the result is good, but at least add for example when objects fall on the field collision so that a light appears like this video site. I threw off the project here. if you know, can you do it? vel_color_Cd.hip
17. ## simulation Slow Viewport Sim. Quick Sim when entering specific frame

Hi Daniel, I had a quick peek at your file yesterday, you resampled the boxes to a very high detail. With a Resample SOP node. Then you packed them and sent to DOP. I don't think that it is necessary and it slows down the DOP a lot. You may check the tutorial, what is the purpose of their Resample (and then Fuse), and how it should be used.
18. ## VDB combine intersection/difference not working cleanly

Thanks--unfortunately, that didn't work in the final project (the box is sized to the actual object I'm mangling). I tried transforming everything down to half size and doubling VDB resolutions to see if your approach worked, but the result was the same.
19. ## VDB combine intersection/difference not working cleanly

Just reducing the size of the box, who is unnecessary big IMO, work for me. I've no explanation.
20. ## [Solved] Python ordered Menu in new Folder and Labels

Found the solution I had to change the Ordered Menu to String. Running all fine now. I added the files if someone wanna check out and maybe improve create_project_v002.hdalc create_project_v002.hiplc
21. ## checking if there is a volume before moving to the next step

I push a geometry really hard, until vdbfrompolygon breaks, but that's ok, when it works it's great, when it doesn't, the volume doesn't even show up, tough luck, we move to the next one. So it's a for each loop, and I need to have a roadblock, a checkpoint, where I ask each vdbfrompolygon if there is a volume at all before proceeding to heavier noise computations: - no volume? abort and move to the next one in the loop - there is volume? cool, proceed with the rest of the steps Sometimes there are very tiny bits of volume, these count as no volume for me. I could let it run for all and only collect the good ones at the end and delete the rest, but it didn't sound very Houdini for me, there should be a clever way of only proceeding with the ones that have volume.
22. ## VDB combine intersection/difference not working cleanly

I'm sure the answer to this will be something so easy, obvious, and profoundly stupid that my family and friends will all disavow having ever known me, but I'm stymied. I am using an animated noise to create a lumpy VDB fog field, which I convert to SDF and then use VDB Combine to cut out part of a hero model. I'm cutting it into two interlocking parts, using SDF Union Subtract for one side and SDF Union Intersection for the other, and I will subsequently assign a different material to each part. Originally I got it set up, no problem, with a standard AAnoise. I'm trying to get it set up with a periodic noise so I can loop it. The problem is that at the VDB combine stage, it doesn't subtract or intersect cleanly. You can tell something is happening, as there are little dotted lines on the resulting surface, and the occasional hole, but it's not cutting it out like I would like. I've tried different resolutions with the VDB from Polygons and that doesn't seem to make a difference. (I've actually run into this before, but I'll either rebuild the Volume VOP or fudge some numbers and it goes away. No such luck here.) What obvious, stupid thing am I doing wrong so that the VDB combine isn't working like I'm hoping? Thanks for help and forebearance! sdf_union_problems.hiplc
23. ## FLIP Particles sticking on a animated surface (And staying there!)

Just to continue updating this while I try to find a solution here's what I come across for resources: Been on the hunt for something that something sticks to an animated surface with velocity and doesn't full off unless it's set to. It'll also need to resolve quickly, because it will be used for animation. (The below all include .hip files that work on H18) 1) This method uses a popdrag for air resistance plus some other methods that work well to keep particles smoothly flowing across a surface. Suffers from animation really throwing it out of wack. When particles fell off the surface because of rotation in animation from the collision object it caused them to have very strange behavior (They kind of just flated in the air in a strange pattern). I didn't dig too much into this, but didn't seem very CPU taxing and did do a good job of smoothly flowing surfaces. https://www.sidefx.com/forum/topic/24897/ (Hip File) https://www.sidefx.com/forum/attachment/2540103a248b6325ae9c84345748756cbb800e33/ 2) A method that converts your geo to a fog density, uses a volume wrangle to control the density of the fog and uses that as a stick mask. Seems to be a bit more of a taxing method as the default sims example are simple, yet take a while per frame then other methods listed. May of just been the scene setup. Works well, but a simple rotation caused all particles fall off. Had great sticking effects with good control, but I wasn't able to easily find a method to get these to stick to an animated surface during a 180 rotation on the sphere. https://www.sidefx.com/forum/topic/33954/ (Hip file) https://www.sidefx.com/forum/attachment/dc1b85ffd5ead04d635ddb117ec8eff5e3d81399/ 3) Looking somewhat similar to the 2nd method above, converts an area to a gas field and uses that as a stick mask. Goes about it a bit different way - blasts off the section and uses a pryo node to turn it into density, but like the first method, a rotation caused particles to fall out. Scene simmed pretty fast, maybe due to the areas of selection being converted to a fog being smaller.. (Hip file) https://forums.odforce.net/applications/core/interface/file/attachment.php?id=44804 4) Particles really *stick" right where they hit, and the sim was very quick. Doing a rotation did cause them to come off, it didn't make all of them. I'll have to mess around some more with the settings on this. Uses a Geometry VOP DOP and sample collision field for every particle . Might start digging into this method. (Hip File) https://forums.odforce.net/applications/core/interface/file/attachment.php?id=17044 5) Have not tested this yet because it's not free. Considering picking this up but not sure if it would work for me. It's a scene for \$33. It's more about surface adhesion versus *sticking* though so it may not have what I need. Can't speak to much becasue I haven't used it. Benchmarks show it to resolve pretty quickly though and add very little onto total sim times. https://gumroad.com/l/Oejcb
24. Yesterday
25. ## Control forces by conditions

Hey I had this come up a few times today and I was wondering what was the best way to tackle it. I am doing a melting sim of an object thats floating in space. I am using temperature to heat the FLIP and start the melting process. if use gravity then the whole thing starts moving from the start and not just the heated parts. I was thinking if I could just apply the forces based on temperature then that would would be ideal. I tried something like this in the pop wrange but its giving me erratic results. float hot = @temperature; if (hot>1) {@v *= 3;}; Also whats the equivalent of the the geometry spreadsheet in dops, if I wanted to see the values of the temperature or any attribute. I can visualize as color but would be nice to get some numbers. Cheers!
26. ## [Solved] Python ordered Menu in new Folder and Labels

Hey, sry for asking again... I did lots of tutorials about python basisc the last days and I get more into it. I had a running "Create folders Script" working and right now I try to move all the code into an HDA / Python Modul. But suddenly I dont get the labels of my ordered menu and also the numbers dont start from 1, but from 0... The only thing I actually did, was to copy the code from the NULL into the HDA Module and the parameters are in a subfolder to get more order inside the HDA. The others functions work just fine and do as they should - just the "create_project_folders" function doesnt work. Is there some syntax or logical problem? Thx edit: Scene/HDA files added. create_project_v001.hdalc create_project_v001.hiplc
27. ## crazy bright spots in volume

Maybe try to clamp the volume rather than absolute value. I know volumes can render strangely with negative values.
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