DOP Vellum

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Solver

Vellum XPBD is expansion of grain PBD - position base dynamic. Points (like in pops) + constraints. Extinvtion of grain solver. For CPU / GPU.

basic PBD algorithm (1st order) issues with damping out energy miss in simulation
1 OldP = P
2 P = P+v*TimeInc
3 Update P to satisfy constraints (integration order here) and resolve collisions
4 v=(P-OldP)
  • Parameters are not global. Size and density matter (if resolution of geo increasse » mass chancge, constrains: number, input, itters.)
  • Mesh resolution change: 1) mass of each point 2) number of constraints (properties/impact on iterations) (Mass > calculate varying)
  • UV direction is importatnt! cloth behave depends on the grain of fabric. Keep UV straight (against grain or cross-cut) cause more or less (weeknes of cross cut. garment will be more visible!!) in 45 degree will collapse not stiff. (Enable Warp and Weft)
  • Thickness not bigger than point distance. (Visual thickness param on constraints or solver or postprocess)
  • You can write initial attribs to points of geometry like velocity
  • You can enter solver and manage forces inside work with POP forces

Solver

[Vellum Solver] DOP

  1. GEOMETRY
  2. CONSTRAINT
  3. COLLISION

stress - estimated work per constraint

Common

Velocity Damping -
Staic Friction - tarcie 0.5 mało / 10 dużo i przywiera

Substeps - (best but most expensive) How many times peer fram simulation take place More expensive, but gives a better solve - especially for higher stiffness values. Increase 5+ for grains (when incresed you can try to decrease cosntr iters)
Constraint Iterations - Increase for higher stiffness value to control excessive deformations - great for cheaper solver at high resolutions
Smoothing Iterations - to smooth out errors of excessive deformations, or constraint errors (when settings are bad) apply ioon dist constr. and chip (Jacobi style solve like grain) but make less stiff

Collision Passes - Uses with the Detangle sop or complex collision (lower frequency iterations) - complicated and expensive - increase when collisions are fighting against constraints or other collisions!! However, its probably better to increase substeps and decrease constraint iterations for a more accurate solve - and to reduce load on the constraints - but is more expensive

Advanced

  • first order integration - less acurate . cheap. simple / artefacts for linear motion (dampness energy)
  • second integration - loose less energym, fewer iteration , sometimes cause bounce ie with collision
stress to high:  
- up substeps - decrees changess rate . Try it first
- constraint itter - more time to solver what is correct postition
Advancde

Second order is more precisem, but canhav issues on colllsion, (bounce) if that turn on max accel

Nodes

[Vellum Object] DOP

create object

[Vellum Source] DOP

Create frame can import obj everth frame by emition type like particles (can read particles without it but) it gives you a sop path. !!!!!!!!! ``


break treshold in sop solver https://youtu.be/iHtdex9kM-A?t=1004

add contrtaint https://youtu.be/iHtdex9kM-A?t=1664

Source

Import:

  • SOP Path + Constraint Path can be [Vellum Constrain]

Forces

Drag - if stuff in simulation have to much energy you can increse drag !!!!

Export:

[DOP Import Fields] SOP

Usualy u have 2 of this connected to VellumI/O with geo an constraints objects.

  • DOP node from: VellumObject
Import:
  • Field ConstraintGeometry // Import one field: only for constraints

VEX

f@friction
i@weld = -1 - same as stop
i@layer layer shock on solver
v@v = 1; - take speed directly from sop

  • (prim) f@stiffness = 1000.0; // set inputs
  • (points) i@stopped = 0; /
  • (points) i@pintoanimaion = 0; - break constraints
  • Pop Wrangle v@force
  • (points) s@breaktype = "stretchstress";

Setups