ZOZO's Contact Solver 🫶

⚙️ Simulation Parameters¶

Application-wide simulation parameters. Accessed via frontend.App.get_default_param() and overridden per session with session.param.set(key, value) / session.param.get(key) (see frontend.ParamManager). Keys use hyphens, not underscores.

disable-contact¶

Key	`disable-contact`
Default	`False`
Label	Disable Contact
Description	When enabled, the simulation will not perform any contact detection.

keep-states¶

Key	`keep-states`
Default	`10`
Label	Keep States
Description	Number of simulation states to keep in the output directory.

keep-verts¶

Key	`keep-verts`
Default	`0`
Label	Keep Vertices
Description	Number of vertex data files to keep in the output directory. 0 means no limit (unlimited). Minimum is 1 to ensure visualization.

dt¶

Key	`dt`
Default	`0.001`
Label	Step Size
Description	Step size for the simulation. Small step size increases accuracy, large step size increases speed but may cause solver divergence.

inactive-momentum¶

Key	`inactive-momentum`
Default	`False`
Label	Inactive Momentum
Description	Enable inactive momentum mode for the simulation. Adjusts step size and disables inertia.

playback¶

Key	`playback`
Default	`1.0`
Label	Playback Speed
Description	Playback speed. 1.0 is normal, >1.0 is faster, <1.0 is slower.

min-newton-steps¶

Key	`min-newton-steps`
Default	`0`
Label	Lower Bound of Newton Steps
Description	Minimal Newton’s steps to advance a step. Recommended 32 if static friction is present.

target-toi¶

Key	`target-toi`
Default	`0.25`
Label	Target Accumulated Time of Impact (TOI)
Description	Accumulated TOI threshold for Newton’s loop termination.

air-friction¶

Key	`air-friction`
Default	`0.2`
Label	Air Tangental Friction
Description	Ratio of tangential friction to normal friction for air drag/lift.

line-search-max-t¶

Key	`line-search-max-t`
Default	`1.25`
Label	Extended Line Search Maximum Time
Description	Factor to extend TOI for CCD to avoid possible solver divergence.

constraint-ghat¶

Key	`constraint-ghat`
Default	`0.001`
Label	Gap Distance for Boundary Conditions
Description	Gap distance to activate boundary condition barriers.

constraint-tol¶

Key	`constraint-tol`
Default	`0.01`
Label	Moving Constraint Minimum Gap Tolerance
Description	This factor is multiplied to the constraint gap to determine the CCD tolerance for moving constraints.

fps¶

Key	`fps`
Default	`60.0`
Label	Frame Per Second for Video Frames
Description	Frame rate for output video.

cg-max-iter¶

Key	`cg-max-iter`
Default	`10000`
Label	Maximum Number of PCG Iterations
Description	PCG solver is regarded as diverged if this is exceeded.

cg-tol¶

Key	`cg-tol`
Default	`0.001`
Label	Relative Tolerance for PCG
Description	Relative tolerance for PCG solver termination.

ccd-eps¶

Key	`ccd-eps`
Default	`1e-07`
Label	ACCD Epsilon
Description	Small thickness tolerance for ACCD gap distance checks.

ccd-reduction¶

Key	`ccd-reduction`
Default	`0.01`
Label	CCD Reduction Factor
Description	Factor multiplied to the initial gap to set the CCD threshold.

ccd-max-iter¶

Key	`ccd-max-iter`
Default	`4096`
Label	Maximum CCD Iterations
Description	Maximum number of iterations for ACCD.

max-dx¶

Key	`max-dx`
Default	`1.0`
Label	Maximum Search Direction
Description	Maximum allowable search direction magnitude during optimization.

eiganalysis-eps¶

Key	`eiganalysis-eps`
Default	`0.01`
Label	Epsilon for Eigenvalue Analysis
Description	Epsilon for stable eigenvalue analysis when singular values are close.

friction-eps¶

Key	`friction-eps`
Default	`1e-05`
Label	Epsilon for Friction
Description	Small value to avoid division by zero in quadratic friction model.

csrmat-max-nnz¶

Key	`csrmat-max-nnz`
Default	`10000000`
Label	Maximal Matrix Entries for Contact Matrix Entries on the GPU
Description	Pre-allocated contact matrix entries for GPU. Too large may cause OOM, too small may cause failure.

frames¶

Key	`frames`
Default	`300`
Label	Maximal Frame Count to Simulate
Description	Maximal number of frames to simulate.

auto-save¶

Key	`auto-save`
Default	`0`
Label	Auto Save Interval
Description	Interval (in frames) for auto-saving simulation state. 0 disables auto-save.

barrier¶

Key	`barrier`
Default	`'cubic'`
Label	Barrier Model for Contact
Description	Contact barrier potential model. Choices: cubic, quad, log.

friction-mode¶

Key	`friction-mode`
Default	`'min'`
Label	Friction Combination Mode
Description	How to combine the friction coefficients of two contacting elements. Choices: min, max, mean. Default min preserves the prior behavior (the more slippery side wins).

stitch-stiffness¶

Key	`stitch-stiffness`
Default	`1.0`
Label	Stiffness Factor for Stitches
Description	Stiffness factor for the stitches.

air-density¶

Key	`air-density`
Default	`0.001`
Label	Air Density
Description	Air density for drag and lift force computation.

isotropic-air-friction¶

Key	`isotropic-air-friction`
Default	`0.0`
Label	Air Dragging Coefficient
Description	Per-vertex air dragging coefficient.

gravity¶

Key	`gravity`
Default	`[0.0, -9.8, 0.0]`
Label	Gravity Vector
Description	Gravity acceleration vector (solver Y-up).

wind¶

Key	`wind`
Default	`[0.0, 0.0, 0.0]`
Label	Wind Force
Description	Wind force vector (XYZ).

include-face-mass¶

Key	`include-face-mass`
Default	`False`
Label	Flag to Include Shell Mass for Volume Solids
Description	Include shell mass for surface elements of volume solids.

fix-xz¶

Key	`fix-xz`
Default	`0.0`
Label	Whether to fix xz positions
Description	Fix xz positions for falling objects if y > this value. 0.0 disables. Use an extremely small value if nearly a zero is needed.

fake-crash-frame¶

Key	`fake-crash-frame`
Default	`-1`
Label	Fake Crash Frame
Description	Frame number to intentionally crash simulation for testing. -1 disables.