player-physics

name

player-physics

description

Apply physics forces to the player in Decentraland scenes. Impulses (one-shot pushes), knockback (push away from a point with falloff), continuous forces (wind tunnels, anti-gravity, lift, levitation, hover), timed forces, and repulsion fields. Use when the user wants launch pads, knockback on hit, wind zones, gravity fields, jumps, lifting/floating the player, pushing the player up/sideways/back, hover effects, or any scene-applied force on the player. THIS is also the right skill when an agent's first instinct is to mutate `Transform` on `engine.PlayerEntity` to move/lift/push the player — that does NOT work (the player Transform is engine-controlled and read-only); use the Physics API instead. Do NOT use for player movement speed (see player-avatar AvatarLocomotionSettings) or platform movement (see animations-tweens).

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.

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.addEntity()
Physics.applyForceToPlayer(lifter, Vector3.create(0, 1, 0), 12)  // continuous upward force
// 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. 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.

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

Trigger-zone collider layers — which player fires the trigger

Physics.* always affects the local player. When you drive forces from a TriggerArea, the collider mask decides which avatars fire the callback (verified in test scene 5,5-collider-layers):

Mask	Fires for
ColliderLayer.CL_MAIN_PLAYER	the local player only
ColliderLayer.CL_PLAYER	remote avatars only (NOT the local player)
CL_PLAYER | CL_MAIN_PLAYER	both local and remote
ColliderLayer.CL_PHYSICS	never fires for any avatar (targets scene mesh/walls, not characters)

Prefer CL_MAIN_PLAYER for player-physics trigger zones. Because the callback then only fires for the local player, you do not need a remote-vs-local guard, and the force is applied to the one avatar it can affect. A launch pad using CL_PLAYER alone will NOT fire for the local player (only for remote avatars), so it never launches the person standing on it — a common bug.

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
• Use CL_MAIN_PLAYER on physics trigger zones (see table above) so the callback fires only for the local player. result.trigger?.entity is the entity that entered; if you instead use CL_PLAYER | CL_MAIN_PLAYER, guard with result.trigger?.entity === engine.PlayerEntity to apply physics only when the local player is the one who entered. Note: result.triggeredEntity is the trigger area's OWN entity, not the entity that entered — comparing it to PlayerEntity never distinguishes the entrant.
• A negative knockback magnitude creates a pull/gravity well effect
• Multiple forces from different entities stack independently

For full code examples (launch pad, wind tunnel, repulsion field, coordinate conversion), see {baseDir}/references/physics-patterns.md.