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Dave Stewart

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About Dave Stewart

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    Seattle, WA
  • Interests
    Music (I play mandolin and piano), Photography, 3D (FX particularly), Gaming (PC mainly), Hiking, Paddling

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  1. FLIP Viscosity - Collision object grid stepping artifacts

    Thanks for taking a look at this guys! It seems that it may be a limitation of the viscosity solver, as it's decoupled from the pressure solve. Sounds like this may get addressed in a future version though! https://cs.uwaterloo.ca/~elariono/stokes/index.html I'll go ahead and submit the file to SFX to see what they say about it. Nigel, increasing substeps doesn't seem to have any affect on the artifacts. Atom, it could be that or just a velocity matching issue relative to the grid scale. Got some interesting thoughts on this in the Houdini Artists FB group. Anthony, I did try that and it helps with the fluid surface/collision interface, but not when the artifacts appear on the outside surface of the fluid as it gets very thin. Cheers, --Dave
  2. Hi All! I'm wondering if anyone has run into this and found a good solution, it's been popping up in my low-to-mid viscosity sims for a while. Perhaps I'm missing something stupidly obvious? Collision geo/field are fine and the interface between fluid and collision object looks great before turning on viscosity, then I get these grid artifacts that are tough to get rid of. Reducing Surface Extrapolation way down in Volume Collisions helps but doesn't completely remove the artifacts. Also, using a high slip-on-collision value helps, but I usually don't want the sliding behavior with sticky viscous fluids. Reducing Grid Scale reduces the relative grid size and helps too, but the artifacts are still there, just smaller. Attached file is somewhat of a worst-cast example, just curious if other folks have dealt with this before. I know I can run some post-sim tweaks to clean up the collision surface intersection, but I've also noticed that the artifacts reveal themselves on the outer surface of the fluid if it gets thin enough, which is not so easy to fix... 01 - viscosity disabled 02 - viscosity enabled 03 - viscosity enabled, surface extrapolation 0.01 Thanks in advance for any help/ideas!! --Dave DStewart_FLIP_ViscousCollisionStepping.hip
  3. Surface tension and viscosity

    Here's a simpler (maybe? Maybe not...) setup sourcing the viscosity point attribute directly into the GasFieldVop using PCOpen/filter. I still think the other solution is better, but this avoids the memory overhead of adding an additional field I guess... --Dave pp_st_ds_PopVOPs_Simpler.hiplc
  4. Surface tension and viscosity

    Here's another version using PopVop/GasFieldVop instead of wrangles... hope it helps clarify the process! Set this up *very* quickly so let me know if I missed anything. Should be able to drive the surfacepressure field directly from the viscosity field, but the values would probably need adjusting in the 'fit' node. --Dave pp_st_ds_PopVOPs.hiplc
  5. Surface tension and viscosity

    Pazuzu's file, slightly modified, would let you drive the surface tension field values based on a point viscosity attribute or whatever. Makes for some interesting shaping by the end! See attached modded file... --Dave pp_st_ds.hip
  6. Resample curve by width/pscale

    Love these explorations! Looking forward to seeing an example of a CHOPs solution, seems ideal for this task. Need to learn more CHOPs, not enough time in the day...
  7. Resample curve by width/pscale

    Here's another hacky way to do this, abusing a rest attribute to restore point positions after scaling by inverted pscale/resampling. Minimal code at least... --Dave resample_withRest_DS.hiplc
  8. Flip fluid: Setting an attribute once at birth

    Correct! That solution would be if you're sourcing from geometry or volumes, and the FLIP particles are created from that data and not from source points, as is the case with the "FLIP fluid from object" and "FLIP tank" shelf tools. Glad you got it working! --Dave
  9. Flip fluid: Setting an attribute once at birth

    You could also plug the expression $F==2 into the "Activation" of a Pop VOP/Wrangle and set your attributes in there. It'll run once and set the attributes on frame 2 (frame 1 doesn't work as the sim hasn't run yet?) --Dave
  10. Differential curve growth

    They taste much better than they look, I promise!! --Dave
  11. Differential curve growth

    Nice setup and render DaJuice! We have a sweet 3D printer here at work, figured it was about time I learned how to print something... First of many I hope! --Dave
  12. FLIP - Mesh Improvement Tips? (stripes on viscous)

    Yo Joh! <ducks and runs> I've found it really difficult to get initially highly-viscous sims to smooth out, even with really extreme settings, while still preserving folds/creases. Really curious if you guys figure anything else out on this. Alvaro, you may want to ditch the shelf setup for meshing and build a custom VDB setup that lets you better mask the VDB smoothing based on curvature/laplacian analysis. Hoping that H16 includes better meshing tools that are tailored to small-scale/viscous sims... --Dave
  13. Excellent work, excited to see the finished short! I'm always amazed by folks like yourself that can keep long-term focus going on a project like this and actually finish it. Funny on the turning 40 thing, I'm in the same boat, and was also getting pretty bored after using 3DSMax since v1. I've attached a setup I'm playing around with that might give you some ideas. Needs more work to be sure and there are probably better ways to achieve this, but it's a start. Be warned that it will want to cook the entire 100 frames no matter what frame you're on, due to a time shift node I have in there. Let me know if you have any questions about the setup... Can't help ya with the sprite rendering unfortunately, but isn't there a sprite SOP as well? May need to figure that out to actually render the sprites. --Dave DStewart_GrainsUpresExample.hip
  14. FLIP - Emitter is Hollow

    Alvaro, is your emitter object watertight? Also, you need to turn off Minimum Distance in the create_surface_volume node, "SDF from geometry" tab. Here's a quick recreation, works here... --Dave DStewart_FLIP_SolidEmitter.hip
  15. Offset Pulse timing

    This is pretty easy, see attached. The Mantra Surface and Principled shaders both have a "use packed color" option in the Diffuse section, which grabs the color values from the points that represent each packed primitive. This example applies random colors to the points after packing, which seems to work just fine. Wonder if there's a way to see this represented in the viewport vs. at render time? --Dave DStewart_PackedGeo_RandomColors.hip