The Engineering of 120 FPS Viscoelastic Soft-Bodies on Apple Metal

A technical breakdown of continuum mechanics, mass-spring volume conservation constraints, and compute shaders on iOS.

Finite Element Continuum Approximations

Simulating deformable soft bodies in real time on mobile hardware is historically computationally prohibitive. Standard finite element methods (FEM) require inverting large stiffness matrices that drain battery and drop frame rates below acceptable thresholds.

Jellify implements an optimized Position Based Dynamics (PBD) solver executed directly on Apple Metal Compute kernels. Rather than tracking internal stress tensors through differential integration, PBD manipulates vertex positions directly using geometric projection constraints.

Hydrostatic Volume Preservation

A classic visual flaw in amateur jelly simulations is 'volume loss'—when pressed, the model simply shrinks into itself. Real organic matter is nearly incompressible (Poisson ratio ν ≈ 0.499).

In Jellify, a global hydrostatic pressure constraint monitors the signed tetrahedron volume sum across the entire mesh. When an external contact force compresses vertices inward, an equal and opposite expansion displacement is projected outward along neighbor surface normals, causing the sides to realistically swell.

Dirty-State Physics Sleep Architecture

To preserve iPhone battery life during extended meditation sessions, Jellify incorporates an intelligent kinematic sleep monitor. When vertex velocities fall below 0.001 m/s for more than 120 consecutive frames, GPU compute pipelines are put to sleep, reducing compute power draw to zero until your next touch event.