dcl-regenesislabs/player-physics

Player Physics in Decentraland

Apply forces to the player's avatar using the Physics API from @dcl/sdk/ecs. All physics operations affect the local player only.

Authoring split

Force calls are runtime — they live in src/index.ts. The trigger entities that cause forces (the launch pad, the wind tunnel volume, the repulsion field marker) are static placements and belong in main-entities.ts with a Transform (and optional MeshRenderer / GltfContainer). Wire pointer/proximity events or trigger systems in src/index.ts to call the Physics.* methods.

Why this skill exists — the Transform mistake

The player's Transform (on engine.PlayerEntity) is engine-controlled and read-only from scene code. Writing to it via Transform.getMutable, Transform.createOrReplace, or direct .position / .rotation mutation silently does nothing — the code compiles, the system ticks, no error is thrown, and the avatar never moves.

If your goal is to lift, float, push, knock back, or apply any sustained force to the player, use this skill's Physics API. For instant teleports / smooth slides to a specific position, use movePlayerTo from ~system/RestrictedActions (skill: player-avatar).

// WRONG — has no effect in-world
const t = Transform.getMutable(engine.PlayerEntity)
t.position.y += 0.1   // ignored every frame

// CORRECT — lift the player upward
import { Physics } from '@dcl/sdk/ecs'
import { Vector3 } from '@dcl/sdk/math'
Physics.applyImpulseToPlayer(Vector3.create(0, 50, 0))         // one-shot upward launch
// or, sustained lift / hover:
const lifter = engine.getEntityOrNullByName('hover_zone')      // named entity from main-entities.ts
if (lifter) Physics.applyForceToPlayer(lifter, Vector3.create(0, 1, 0), 12)
// stop with: Physics.removeForceFromPlayer(lifter)

Impulse (One-Shot Push)

Apply a single instantaneous force with Physics.applyImpulseToPlayer(direction, magnitude?). Direction is auto-normalized when magnitude is passed separately. Multiple calls within the same frame are accumulated. Use for launch pads, jumps, and explosions.

Knockback (Push Away from a Point)

Push the player away from a source position with Physics.applyKnockbackToPlayer(sourcePos, magnitude, radius?, falloff?). Direction is computed automatically from source to player.

KnockbackFalloff Options

| Falloff | Behavior | |---|---| | KnockbackFalloff.CONSTANT | Same magnitude at any distance within radius (default) | | KnockbackFalloff.LINEAR | Smooth linear decrease to 0 at the radius edge | | KnockbackFalloff.INVERSE_SQUARE | Sharp, physically-realistic drop-off |

If the player is exactly at the source, they are pushed straight up. A negative magnitude pulls the player toward the point (gravity well). The same falloff values apply to applyRepulsionForceToPlayer().

Continuous Force

Apply a persistent directional force identified by an entity (the force "owner"). Multiple forces from different entities stack.

• Apply: Physics.applyForceToPlayer(entity, direction, magnitude?)
• Remove: Physics.removeForceFromPlayer(entity)

Use with trigger zones for wind tunnels, conveyor belts, and gravity fields. The owner entity is just an ID handle for later removal — typically the named main-entities.ts entity representing the trigger zone.

Timed Force

Apply a force for a fixed duration: Physics.applyForceToPlayerForDuration(entity, seconds, direction, magnitude?). Expires automatically.

Repulsion Force

Continuous push away from a fixed point with distance-based falloff, recalculated each frame: Physics.applyRepulsionForceToPlayer(entity, position, magnitude, radius). The position must be passed explicitly — not read from the entity's Transform automatically. Remove with Physics.removeForceFromPlayer(entity).

Coordinate Conversion (Local to World Direction)

Convert local direction to world space with Transform.localToWorldDirection(entity, localDir). Use when pushing relative to an entity's orientation (e.g. "forward from this cannon").

Quick Reference

| Method | Type | Description | |---|---|---| | Physics.applyImpulseToPlayer(dir, mag?) | One-shot | Instant directional push | | Physics.applyKnockbackToPlayer(pos, mag, radius?, falloff?) | One-shot | Push away from point | | Physics.applyForceToPlayer(entity, dir, mag?) | Continuous | Persistent push while active | | Physics.removeForceFromPlayer(entity) | Control | Stop a continuous force | | Physics.applyForceToPlayerForDuration(entity, secs, dir, mag?) | Timed | Force that expires automatically | | Physics.applyRepulsionForceToPlayer(entity, pos, mag, radius) | Continuous | Distance-based push from point | | Transform.localToWorldDirection(entity, dir) | Utility | Convert local direction to world space |

Best Practices

• Use applyImpulseToPlayer for one-off events (jump pads, explosions, hits).
• Use applyForceToPlayer + removeForceFromPlayer with trigger zones for areas (wind tunnels, conveyor belts).
• Use KnockbackFalloff.LINEAR for most area effects — it feels natural and predictable.
• Always check result.trigger?.entity !== engine.PlayerEntity in trigger callbacks to only affect the local player.
• A negative knockback magnitude creates a pull/gravity well effect.
• Multiple forces from different entities stack independently.