/godot-2d-physics

Collision layers and masks

Mental model

# collision_layer: What broadcast channels am I transmitting on?
# collision_mask:   What broadcast channels am I listening to?

# Player: layer=0b0001, mask=0b0110 (hears enemies + world)
# Enemy:  layer=0b0010, mask=0b0101 (hears player + world)

Layer = who I am. Mask = who I detect. Setting both to the same value is usually wrong.

Helpers (prefer over magic bitmasks)

func setup_player_collision() -> void:
    set_collision_layer_value(1, true)   # I am layer 1
    set_collision_mask_value(2, true)    # Detect enemies
    set_collision_mask_value(3, true)    # Detect world

func enable_layers(base_layer: int, count: int) -> void:
    var mask := 0
    for i in range(count):
        mask |= (1 << (base_layer + i - 1))
    collision_mask = mask

Scripts: collision_bitmask_helper.gd, collision_layer_matrix_manager.gd.

Common patterns

# Projectile hits enemies, ignores other projectiles
extends Area2D
func _ready() -> void:
    set_collision_layer_value(4, true)  # Projectiles
    set_collision_mask_value(2, true)   # Enemies only

Name layers in Project Settings before hardcoding layer indices in team docs.

Edge cases