Simulation

simulation

Purpose

Add the natural world: falling, flowing, burning, tearing, weather — only when faking is harder or visibly worse. Sims are powerful, expensive, and cache-disciplined.

Scope

D87–D99, S-11 physics infrastructure, S-12 soft bodies, fire/smoke tables in Depth 35. Hero garment construction stays in costume-groom; this skill owns shared physics and non-costume sims. Effect design is vfx.

Activation Conditions

• Rigid body, soft body, cloth physics, hair physics, fluid, ocean, smoke, fire, fracture, debris, rain, force fields, caches
• Use simulation

Non-Activation Conditions

• Animation body performance (→ animation) — required before most sims
• Magic design / layered impact recipe (→ vfx)
• Fake rain/flags (decision 5.6) — do not open a sim

Instructions

1. Fake first (5.6 / 5.18). Distant flags, puddles, rain, dust motes: particles/shaders/drivers.
2. Simulate last: final-ish meshes + final animation.
3. Infrastructure (D88 / S-11): gravity, force fields catalog (Force, Wind, Turbulence, Vortex, Magnetic, Harmonic, Curve guide), collision, caching, scale in meters.
4. Collision proxies (low-poly) are standard.
5. Bake to disk in cache/, named per shot+version. Never rely on memory cache for production.
6. Rigid (D89): animated vs dynamic; passive colliders; apply scale.
7. Soft (D90 / S-12): goal vertex group; not for fabric (use cloth); low-poly sim + subdiv display.
8. Cloth (D91) / hair (D92): coordinate with costume-groom.
9. Fluids (D93) / water (D94): Mantaflow for hero splash/pour; Ocean modifier for seas; ripple shader for puddles.
10. Smoke (D95) / fire (D96): Mantaflow gas; tuning table in Depth 35.3. Domain size = cost.
11. Destruction (D97): Cell Fracture + rigid; debris (D98) as secondary chunks + dust particles.
12. Environmental (D99): weather, leaves, ambient — prefer particles/GN.
13. Checklist: scale → gravity → colliders → force fields → quality → bake → verify.

Procedures

Production rules (chapter in 8 lines)

1. Scale meters. 2. Fake first. 3. Proxies. 4. Bake disk. 5. One sim owner per shot. 6. Domain as small as possible. 7. Cache versioned. 8. QC a playblast before render.

Fire/smoke

Fuel vs smoke density, temperature, vorticity, dissolve, noise. Render via Principled Volume. Small domain, high res only on hero.

Decision Logic

If the audience cannot tell it was faked at shot size, fake it. Hero cloak, hero explosion, hero pour: sim.

Inputs

• Locked animation, collision meshes, scale master, shot camera (frustum culls domain), style (stylized fire often fake)

Outputs

• Caches on disk
• Collision collections
• Settings notes for archive
• Shared state: shot status sim'd; locks.sim

Tools

Mantaflow, Rigid Body World, Cloth, Soft Body, Particles, GN simulation zones, Cell Fracture, force fields. S-11/S-12. Depth 35.

Constraints

Wrong scale = exploding sims. Never sim full-res hero mesh. Never skip bake. Caustics/fire in glass = expensive; warn render-comp.

Edge Cases

• Stylized fire breath: emissive curves + particles (vfx), not Mantaflow.
• Crystal magnetic creature: Magnetic force field (S-11) is a legal gag.

Failure Modes & Fixes

Dependencies

• After animation
• Shared with costume-groom for cloth/hair
• Feeds vfx and render-comp
• Needs blender-foundations scale

Related Skills

costume-groom, vfx, animation, environment, render-comp

Delegation Rules

• Layered impact / magic look → vfx (sim may supply debris/smoke layers)
• Ocean look without sim → environment + lookdev
• If user asked "should I sim this?" → decision-engine 5.6

Examples

• Hero splash: small Mantaflow domain, inflow at contact, foam particles, bake.
• Rainy city: particle rain + wetness, not fluid.

Required Knowledge / Context

• knowledge/domains/ch10-simulation.md
• knowledge/system/02d-depth-supplements.md (S-11 S-12)
• knowledge/depth/ch35-vfx-depth.md (tuning tables)

References to Shared Resources

• workflows/sim-last.md
• decision-engine 5.6 5.18