perf(fp): run skeleton modifiers on the idle frame, not per physics frame

scripts/fp/animals/cat_bodies.gd

@@ -92,6 +92,8 @@ func _bind(b: DB.Body, scene: Node3D) -> void:
 	b.head = b.skel.find_bone("Head")
 	var rig := CAT_RIG.new()
 	rig.name = "CatRig"
+	# The rig runs on the idle frame, not once per physics frame (people_pool.gd says why).
+	b.skel.modifier_callback_mode_process = Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
 	b.skel.add_child(rig)
 	rig.bind(b.skel, scene, CAT_RIG.CAT_TAIL, "Neck")
 	b.rig = rig

scripts/fp/animals/dog_bodies.gd

@@ -176,6 +176,8 @@ func _bind(b: Body, scene: Node3D) -> void:
 	b.head = b.skel.find_bone("Head")
 	b.rig = RIG.new()
 	b.rig.name = "DogRig"
+	# The rig runs on the idle frame, not once per physics frame (people_pool.gd says why).
+	b.skel.modifier_callback_mode_process = Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
 	b.skel.add_child(b.rig)
 	b.rig.bind(b.skel, scene)
 

scripts/fp/player/hero_look.gd

@@ -120,6 +120,8 @@ func _modifier(n: String, bone: String, yaw_lim: float, pitch_lim: float) -> Loo
 	m.transition_type = Tween.TRANS_SINE
 	m.ease_type = Tween.EASE_IN_OUT
 	m.origin_safe_margin = LOOK_SAFE_MARGIN
+	# Runs on the idle frame, not once per physics frame (people_pool.gd says why).
+	_skeleton.modifier_callback_mode_process = Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
 	_skeleton.add_child(m)
 	return m
 

scripts/fp/player/hero_strike_pose.gd

@@ -160,6 +160,9 @@ func _init(
 		_curl.append_array(fist_joints(p_sk, s))
 	_mod = Mod.new(self)
 	_mod.name = "StrikePose"
+	# Runs on the idle frame, after the hand-advanced tree, not once per physics frame
+	# (the web build's catch-up steps would multiply that; people_pool.gd says more).
+	p_sk.modifier_callback_mode_process = Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
 	p_sk.add_child(_mod)
 	_mod.active = false
 

scripts/fp/traffic/people_pool.gd

@@ -212,6 +212,10 @@ func make(ai: int) -> Body:
 		b.root.queue_free()
 		return null
 	b.head = b.skel.find_bone("Head")
+	# Skeleton modifiers (the T0 head look) run on the idle frame with the hand-advanced
+	# mixers; the engine default PHYSICS mode would pay them once per physics frame,
+	# multiplied by the web build's catch-up steps on slow frames.
+	b.skel.modifier_callback_mode_process = Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
 	for n: Node in b.scene.find_children("*", "GeometryInstance3D", true, false):
 		b.meshes.append(n as GeometryInstance3D)
 	var lib: AnimationLibrary = ppl._libs[a.gender]

tools/tests/fp_animals_test.gd

@@ -263,6 +263,18 @@ func _check_lead() -> WK.Walker:
 		rigged and b.ap.has_animation(&"Gallop") and b.ap.has_animation(&"Attack"),
 		"lead: the dog is the rigged %s with its clips and a DogRig" % d.breed
 	)
+	K.check(
+		fails,
+		(
+			b.skel != null
+			and (
+				b.skel.modifier_callback_mode_process
+				== Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
+			)
+		),
+		"lead: the DogRig runs on the idle frame, not once per physics frame"
+	)
+	K.check_modifier_modes(fails, get_root())
 	var worst := 0.0
 	var left := 0.0
 	var n := 0

tools/tests/fp_cats_test.gd

@@ -334,6 +334,18 @@ func _check_spawn() -> LIFE.Cat:
 		dressed and clips and c.body.rig is CB.CAT_RIG and not c.name.is_empty(),
 		"spawn: %s, a %s %s cat in the cat's body and its coat" % [c.name, c.temper, c.coat]
 	)
+	K.check(
+		fails,
+		(
+			c.body.skel != null
+			and (
+				c.body.skel.modifier_callback_mode_process
+				== Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
+			)
+		),
+		"spawn: the CatRig runs on the idle frame, not once per physics frame"
+	)
+	K.check_modifier_modes(fails, get_root())
 	cats.scan(ctx.player.position, false, true, {})
 	var gone := _cat() == null
 	_step(AF.SCAN_S + 0.1)

tools/tests/fp_kit.gd

@@ -426,6 +426,27 @@ static func check(fails: Array, ok: bool, what: String) -> void:
 		fails.append(what)
 
 
+## Every SkeletonModifier3D under root rides a skeleton in the IDLE modifier callback mode:
+## the engine default PHYSICS mode pays each modifier once per physics frame, multiplied by
+## the web build's catch-up steps on slow frames (the day-10 tick-frame attribution).
+static func check_modifier_modes(fails: Array, root: Node) -> void:
+	var mods := root.find_children("*", "SkeletonModifier3D", true, false)
+	var bad := 0
+	for m: Node in mods:
+		var sk := m.get_parent() as Skeleton3D
+		var idle := (
+			sk != null
+			and sk.modifier_callback_mode_process == Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
+		)
+		if not idle:
+			bad += 1
+	check(
+		fails,
+		bad == 0,
+		"every SkeletonModifier3D runs on the idle frame (%d of %d off)" % [bad, mods.size()]
+	)
+
+
 ## Input events for a feature's _unhandled_input: action a pressed.
 static func action_event(a: String) -> InputEventAction:
 	var e := InputEventAction.new()

tools/tests/fp_people_prewarm_test.gd

@@ -60,4 +60,17 @@ func _init() -> void:
 		pe.get("scene_loads") == settled,
 		"a seat after warming initiates no load (still %d)" % settled
 	)
+
+	# The body a seat lends runs its skeleton modifiers (the T0 head look) on the idle frame
+	# with the hand-advanced mixers, not once per physics frame (web catch-up multiplies that).
+	var seated: Array = (pe.get("_pool") as RefCounted).get("_seated")
+	var sk := (seated[0].get("skel") if not seated.is_empty() else null) as Skeleton3D
+	K.check(
+		fails,
+		(
+			sk != null
+			and sk.modifier_callback_mode_process == Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
+		),
+		"a seated body's modifiers run on the idle frame, not once per physics frame"
+	)
 	K.finish(self, "FP_PEOPLE_PREWARM_TEST", fails)

tools/tests/fp_player_test.gd

@@ -63,6 +63,7 @@ func _init() -> void:
 	_check_thin_wall(ctx)
 	_check_stuck(ctx)
 	_check_cam_trunk(ctx)
+	_check_hero_modifier_mode(ctx)
 	K.finish(self, "FP_PLAYER_TEST", fails)
 
 
@@ -1486,3 +1487,20 @@ func _check_cam_trunk(ctx: FpContext) -> void:
 		"a trunk where the camera sat: inside it or looking through it on %d of 240 frames" % bad
 	)
 	K.check(fails, vaultable.is_empty(), "parkour's boxes_near still leaves the trunk out")
+
+
+## The hero's strike-pose and head-look modifiers run on the idle frame, after the
+## hand-advanced AnimationTree, not once per physics frame (the web build's catch-up steps
+## would multiply that).
+func _check_hero_modifier_mode(ctx: FpContext) -> void:
+	var rig: Variant = (ctx.player as PL).avatar.get("rig")
+	var sk := (rig.get("skeleton") if rig != null else null) as Skeleton3D
+	K.check(
+		fails,
+		(
+			sk != null
+			and sk.modifier_callback_mode_process == Skeleton3D.MODIFIER_CALLBACK_MODE_PROCESS_IDLE
+		),
+		"hero: the skeleton's modifiers run on the idle frame, not once per physics frame"
+	)
+	K.check_modifier_modes(fails, get_root())