Terrain physics uses surface drag model

src/equipment/balls/debug_ball/debug_ball.gd

@@ -1,6 +1,6 @@
 extends GameBall
 
-const INFO_FMT := "speed: {0} m/s\nlin.damp: {1}\nang.spd: {2}\nang.damp: {3}\ntime: {4} s\nsurface decay: {5}"
+const INFO_FMT := "speed: {0} m/s\nang.spd: {1}\nsurface: {2}\ntime: {3} s"
 
 @onready var debug_info: Label3D = %DebugInfo
 
@@ -11,10 +11,8 @@ func _physics_process(delta: float) -> void:
 	debug_info.text = INFO_FMT.format(
 		[
 			linear_velocity.length(),
-			linear_damp,
 			angular_velocity.length(),
-			angular_damp,
+			Terrain.Type.keys()[_surface_terrain],
-			_shot_time_s,
+			_shot_time_s
-			terrain_physics.get_decay_factor(_surface_time_s)
 		]
 	)

src/equipment/balls/debug_ball/debug_ball.tscn

@@ -19,6 +19,7 @@ size = Vector2(0.05, 0.05)
 
 [sub_resource type="SystemFont" id="SystemFont_td87w"]
 font_names = PackedStringArray("Monospace")
+subpixel_positioning = 0
 
 [node name="DebugBall" instance=ExtResource("1_gcsxs")]
 script = ExtResource("2_edye5")

src/equipment/balls/physics_ball/game_ball.gd

@@ -14,18 +14,12 @@ enum Type {
 	POWER,
 }
 
-const TERRAIN_DAMPING_EPSILON := 1e-6
+const VELOCITY_SQ_EPSILON := 1e-4
-const MAGNUS_EPSILON := 1e-3
+const MAGNUS_SQ_EPSILON := 1e-3
 
 ## If enabled, ball ability cooldown is only reset at end of shot.
 @export var once_per_shot_ability := false
 
-## Linear damping while in the air.
-@export var aerial_linear_damping := 0.0
-
-## Angular damping while in the air.
-@export var aerial_angular_damping := 0.0
-
 ## Material physics configuration for this ball.
 @export var terrain_physics: TerrainPhysics
 
@@ -64,6 +58,7 @@ var _ability_triggered := false
 var _zones: Array[BallZone] = []
 var _shot_time_s := 0.0
 var _surface_time_s := 0.0
+var _surface_terrain: Terrain.Type
 
 @onready var ability_cooldown: Timer = %AbilityCooldown
 @onready var manual_sleep_timer: Timer = %ManualSleepTimer
@@ -74,9 +69,6 @@ var _surface_time_s := 0.0
 	"res://src/equipment/balls/physics_ball/normal_physics.tres"
 )
 
-@onready var default_surface_linear_damping := linear_damp
-@onready var default_surface_angular_damping := angular_damp
-
 
 ## Should this ball stick to surfaces, rather than bounce?
 func is_sticky() -> bool:
@@ -131,43 +123,45 @@ func _integrate_forces(state: PhysicsDirectBodyState3D) -> void:
 
 		# We want the contact normal which minimizes the angle to the up vector
 		var min_dot := -1.0
+		var primary_body: Node
 		for i: int in range(state.get_contact_count()):
 			var norm := state.get_contact_local_normal(i)
 			var dot := norm.dot(Vector3.UP)
 			if dot > min_dot:
 				min_dot = dot
 				_last_contact_normal = norm
+				primary_body = state.get_contact_collider_object(i)
 
-		# Use first contact to determine terrain properties
+		_surface_terrain = Terrain.from_collision(global_position, primary_body)
-		var primary_body: Node = state.get_contact_collider_object(0)
-
-		var terrain := Terrain.from_collision(global_position, primary_body)
-		var params := terrain_physics.get_params(terrain)
-		if params:
-			linear_damp = params.linear_damping
-			angular_damp = params.angular_damping
-		else:
-			linear_damp = default_surface_linear_damping
-			angular_damp = default_surface_angular_damping
-
-		var decay := 1.0 + terrain_physics.get_decay_factor(_surface_time_s)
-		#linear_damp *= decay
-		#angular_damp *= decay
-
 		_surface_time_s += state.step
 	else:
 		# Ball is in the air
-		linear_damp = aerial_linear_damping
+		_surface_terrain = Terrain.Type.NONE
-		angular_damp = aerial_angular_damping
 		_surface_time_s = 0.0
 
 
 func _physics_process(delta: float) -> void:
 	# Simulate magnus effect
 	var magnus := _magnus_force()
-	if magnus.length_squared() > MAGNUS_EPSILON:
+	if magnus.length_squared() > MAGNUS_SQ_EPSILON:
 		apply_central_force(magnus)
 
+	# Apply drag
+	var params := terrain_physics.get_params(_surface_terrain)
+	if linear_velocity.length() > params.linear_drag:
+		linear_velocity -= params.linear_drag * linear_velocity.normalized()
+	else:
+		linear_velocity = Vector3.ZERO
+	if angular_velocity.length() > params.angular_drag:
+		angular_velocity -= params.angular_drag * angular_velocity.normalized()
+	else:
+		angular_velocity = Vector3.ZERO
+
+	if linear_velocity.length_squared() < VELOCITY_SQ_EPSILON:
+		linear_velocity = Vector3.ZERO
+	if angular_velocity.length_squared() < VELOCITY_SQ_EPSILON:
+		angular_velocity = Vector3.ZERO
+
 	# Keep shot time
 	_shot_time_s += delta
 

src/equipment/balls/physics_ball/physics_ball.tscn

@@ -19,58 +19,56 @@
 
 [sub_resource type="Resource" id="Resource_casfi"]
 script = ExtResource("4_onl6o")
-linear_damping = 0.0
+linear_drag = 0.0
-angular_damping = 0.5
+angular_drag = 1.0
 
 [sub_resource type="Resource" id="Resource_3k63c"]
 script = ExtResource("4_onl6o")
-linear_damping = 0.0
+linear_drag = 0.0
-angular_damping = 8.0
+angular_drag = 0.0
 
 [sub_resource type="Resource" id="Resource_xf73q"]
 script = ExtResource("4_onl6o")
-linear_damping = 0.0
+linear_drag = 0.0
-angular_damping = 2.0
+angular_drag = 1.0
 
 [sub_resource type="Resource" id="Resource_nhn3l"]
 script = ExtResource("4_onl6o")
-linear_damping = 0.0
+linear_drag = 0.0
-angular_damping = 0.1
+angular_drag = 1.0
 
 [sub_resource type="Resource" id="Resource_m3wjo"]
 script = ExtResource("4_onl6o")
-linear_damping = 0.0
+linear_drag = 0.0
-angular_damping = 1.0
+angular_drag = 1.0
 
 [sub_resource type="Resource" id="Resource_h4rld"]
 script = ExtResource("4_onl6o")
-linear_damping = 0.0
+linear_drag = 0.0
-angular_damping = 0.1
+angular_drag = 1.0
 
 [sub_resource type="Resource" id="Resource_j6lib"]
 script = ExtResource("4_onl6o")
-linear_damping = 0.0
+linear_drag = 0.0
-angular_damping = 2.0
+angular_drag = 1.0
 
 [sub_resource type="Resource" id="Resource_7f7ql"]
 script = ExtResource("4_onl6o")
-linear_damping = 0.0
+linear_drag = 0.0
-angular_damping = 8.0
+angular_drag = 3.0
 
 [sub_resource type="Resource" id="Resource_pusmf"]
 script = ExtResource("4_onl6o")
-linear_damping = 1.0
+linear_drag = 1.0
-angular_damping = 24.0
+angular_drag = 10.0
 
 [sub_resource type="Resource" id="Resource_edkxb"]
 script = ExtResource("4_onl6o")
-linear_damping = 0.0
+linear_drag = 0.0
-angular_damping = 1.0
+angular_drag = 1.0
 
 [sub_resource type="Resource" id="Resource_3ngau"]
 script = ExtResource("3_52hui")
-damping_decay_curve = 12.0
-damping_decay_scale = 8.0
 default = SubResource("Resource_3k63c")
 rough = SubResource("Resource_7f7ql")
 fairway = SubResource("Resource_xf73q")

src/equipment/balls/physics_ball/terrain_physics/terrain_parameters.gd

@@ -1,5 +1,5 @@
 class_name TerrainParameters extends Resource
 ## Physical parameters for an individual terrain type.
 
-@export var linear_damping := 0.0
+@export var linear_drag := 0.0
-@export var angular_damping := 0.0
+@export var angular_drag := 0.0

src/equipment/balls/physics_ball/terrain_physics/terrain_physics.gd

@@ -1,9 +1,6 @@
 class_name TerrainPhysics extends Resource
 ## Container for ball behavior parameters when in contact with different terrain types
 
-@export_exp_easing() var damping_decay_curve := 1.0
-@export var damping_decay_scale := 8.0
-
 @export var default: TerrainParameters
 
 @export var rough: TerrainParameters
@@ -41,10 +38,3 @@ func get_params(type: Terrain.Type) -> TerrainParameters:
 			return glass
 		_:
 			return default
-
-
-func get_decay_factor(time: float) -> float:
-	var x := time / damping_decay_scale
-	if damping_decay_curve < 1.0:
-		return 1.0 - pow(1.0 - x, 1.0 / damping_decay_curve)
-	return pow(x, damping_decay_curve)