coltonmil

Perhaps adjusting Rest Length Scale under Stretch could achieve a similar thing. It defaults to 1 which keeps points at their input distances, if you drop it below 1 it should cause them to contract. Edit: Doh, totally missed the last sentence! Hmm, maybe stiffness is set too high for it to properly contract? Vellum is very sensitive to scene scale, so the values for stiffness often have to be wacky.

Hey Kikohs, I'm not able to upload a file at the moment, but hopefully I can help anyways! First thing: your polyextrude is currently only extruding, but not creating a closed object. Make sure "Output Back" on the Extrusion tab is checked to have it create a closed object. VDBfrompolygons requires a closed object to correctly generate a VDB. Next, turn the Distance VDB back on in the vdbfrompolygons. Finally, in your vdbcombine clear the group fields as it will use the surface volume by default (which I believe is what you desire). Let me know if you have any other questions!

Assuming the points you wish to connect have a corresponding id attribute (or something similar), you just merge the points and the Add SOP should do the trick! Set it to the "Polygons" tab, then "By Group" tab within there, set the "Add" drop down to by attribute, and enter the name of your id attribute. If you don't have an id attribute, do all of the above, and instead set "Add" to groups of N points.

Stretching of UVs on extreme vertical changes will always be the weakness of a system using Y Projection UVs. In Alex's example, he doesn't have any vertical displacements nearly as extreme as your example, so that would be why you don't see the degradation you're seeing. The other weakness isn't just UV degradation, but also the lack of much terrain detail in highly sloped areas. I recently completed a project that had very large terrains, with a few extremely vertical mountains. The workflow that I found to work best for this situation is to separate the extreme mountains and map them individually (or sculpt extra detail into them as we did), while keeping as much of the remaining terrain as possible as heightfields. You can use some of the heightfield masks to isolate the large elevation changes, but I was manually selecting areas where the mountains were for separation. This worked in my case as the output was highly driven by concept art, so it needed to be very manually directed. As for texturing, I found exporting the heightfield masks to be very useful. I did a small amount of processing in COPs, but not much, as I preferred to use Nuke to do essentially the same processing. There wasn't much direct texturing work we did with the masks, as we mostly used them to drive scattering of trees, grass, etc. We did use painted texture maps for the rocks and such, and masked them in via shaders. Let me know if you have any specific questions about workflow etc.!

My mistake! I always forget that expressions key with bezier() anim as well, but my method was flawed from the beginning as I was doing + as opposed to * anyways. If you go to both keyframes of your rising anim and change the + to a *, and copy the value from frame 24 to 1, it should fix this problem.

You had all the pieces, just needed the glue to get it together I used your ID attribute that you generated to control the isolation of the points on a specific frame number. This ID effectively acts as a generation frame, so current frame minus this gives you an animation frame that starts each time a point is generated. All of this is controlled through copy stamping, no additional For Each is needed. I also provided a solution in the file for additional randomized Y scale. initialize_anim_H16_v2.hip

You had the right idea with the solver! I did exactly as you were thinking additive velocity that controls a copy stamp that affects an upstream timeshift SOP. Your use of alembic frame is interesting and new to me; I don't have your test abc to see how that works, but you should be able to adapt my setup to work with yours. animation_playback_by_speed_v3.hip

For a fast explosion and thin collisions 10 substeps is actually not super crazy. It'll really be the only way you can get accurate collisions at that level. You can set the max substeps and play with the CFL so it's only doing the full 10 substeps at the beginning of the sim where it needs the detail. If you're looking for a dirty trick, you could make your roof much thicker in the +Y direction for the first couple frames of the explosion, and as the fire ball begins to slow as it breaches the roof, start to scale it back to normal. This may cause some strangeness in the smaller pieces, and negatively effect the way the fireball would wrap around the roof as it blows outwards.

Is it significantly faster to sim with a larger number of simple convex hulls than one complex concave?

Adding density field and using the temperature as density fixed the issue as well. cmil_debug_refl_v001.hiplc

Sorry about that, forgot I'm using a custom vdbfrompolygons, if you just swap in the standard one you should be good!

Got a closer shape using the ideas I posted above! With some overall warping, and playing with the VDB meshing, you might be able to massage this into something like the ref. vexGeoTest_v01.hipnc

Sorry man, I haven't had a lot of time to try out some of the ideas I had, but here's the basis of what I'm thinking: Use this method to create polylines: Do a nearpoints like shown, but then don't connect points that are at the same "level" as each other (or distance from center), so you end up more with these 45 degree connections going inwards like in your ref. Then convert to geo and blend using VDB to get the nice smooth connections like the ref. I'll try and flesh something out more, but this is a great tut to go through regardless

I think it might be more controllable using poly-lines and creatively grouped points to connect everything as opposed to just metaballs like the method I'm doing. I'm trying a couple other things to see what I can come up with, but I'm certain a Houdini genius can swoop in here with a solution readily available We really need a bat-signal type light with a giant H for these guys

Something like this?