mtgodot-poc/project/ui/weapon_trace.gd

# WeaponTrace —— 40250 GameLib/WeaponTrace.cpp 的 Godot 适配层。
#
# 40250 的刀光不是一次性 MSE 特效：AttachWeapon 为可追踪武器创建对象，
# ActorInstance 每帧采样武器实例的刀根/刀尖世界坐标，RenderTrace 再把
# short/long 两条时间轨迹用 cubic spline 拼成 triangle strip。这里保留同一
# 状态边界和参数；渲染坐标在世界空间采样，在当前 PlayerView 局部渲染，
# 因此角色移动时已经生成的尾迹不会被父节点位移二次带走。
extends Node3D

const DEFAULT_LIFETIME := 0.18
const DEFAULT_SAMPLING_TIME := 0.003
const TRACE_COLOR := Color(0.3, 0.8, 1.0, 1.0)

var lifetime := DEFAULT_LIFETIME
var sampling_time := DEFAULT_SAMPLING_TIME
var reach_scale := 1.0 # CActorInstance::__GetReachScale()
var use_texture := false
var texture_path := ""

var _weapon: Node3D
var _playing := false
var _has_geometry := false
var _tip_local := Vector3.ZERO
var _short_points: Array = [] # newest first:刀根
var _long_points: Array = []  # newest first:刀尖
var _vertex_count := 0

var _mesh := ImmediateMesh.new()
var _mesh_instance := MeshInstance3D.new()
var _material := StandardMaterial3D.new()

func _ready() -> void:
	_ensure_render_node()

func _ensure_render_node() -> void:
	if _mesh_instance.get_parent() == null:
		_mesh_instance.name = "WeaponTraceMesh"
		_mesh_instance.mesh = _mesh
		_mesh_instance.cast_shadow = GeometryInstance3D.SHADOW_CASTING_SETTING_OFF
		add_child(_mesh_instance)
	_material.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
	_material.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA
	_material.blend_mode = BaseMaterial3D.BLEND_MODE_MIX
	_material.cull_mode = BaseMaterial3D.CULL_DISABLED
	_material.depth_draw_mode = BaseMaterial3D.DEPTH_DRAW_DISABLED
	_material.vertex_color_use_as_albedo = true
	_mesh_instance.material_override = _material
	_mesh_instance.visible = false

func attach_to_weapon(weapon_node: Node3D) -> bool:
	if _weapon == weapon_node and is_instance_valid(_weapon):
		return _has_geometry
	turn_off()
	clear()
	_weapon = weapon_node
	_has_geometry = false
	_tip_local = Vector3.ZERO
	if not is_instance_valid(_weapon):
		return false
	_has_geometry = _resolve_tip_local()
	return _has_geometry

func detach_weapon() -> void:
	turn_off()
	clear()
	_weapon = null
	_has_geometry = false
	_tip_local = Vector3.ZERO

func turn_on() -> void:
	# 40250 TurnOn only changes the playing flag; the existing tail remains and
	# naturally fades, so combo segments do not pop the trace between swings.
	_playing = true

func turn_off() -> void:
	# 40250 TurnOff deliberately does not Clear(): old samples remain visible
	# until lifetime expiry. Equipment replacement uses detach_weapon(), which
	# is the DestroyWeaponTrace/Clear path instead.
	_playing = false

func set_lifetime(value: float) -> void:
	lifetime = maxf(value, 0.001)
	_trim_expired()

func set_sampling_time(value: float) -> void:
	sampling_time = maxf(value, 0.0001)

func set_reach_scale(value: float) -> void:
	# 40250 applies this scale when extending the trace from the bone matrix;
	# recompute the cached local endpoint so an actor-scale change takes effect
	# before the next sample.
	reach_scale = maxf(value, 0.0)
	if is_instance_valid(_weapon):
		_has_geometry = _resolve_tip_local()

func set_texture(path: String) -> void:
	texture_path = path
	use_texture = path != ""
	_material.albedo_texture = _load_texture(path) if use_texture else null

func use_alpha() -> void:
	use_texture = false
	_material.albedo_texture = null

func use_texture_mode() -> void:
	use_texture = true
	_material.albedo_texture = _load_texture(texture_path) if texture_path != "" else null

func is_playing() -> bool:
	return _playing

func debug_state() -> Dictionary:
	return {
		"playing": _playing,
		"has_geometry": _has_geometry,
		"short_points": _short_points.size(),
		"long_points": _long_points.size(),
		"vertex_count": _vertex_count,
		"lifetime": lifetime,
		"sampling_time": sampling_time,
		"reach_scale": reach_scale,
		"tip_local": _tip_local,
		"tip_length": _tip_local.length(),
		"use_texture": use_texture,
	}

func _process(delta: float) -> void:
	_ensure_render_node()
	var elapsed := maxf(delta, 0.0)
	_age_points(elapsed)
	if _playing and _has_geometry and is_instance_valid(_weapon):
		_sample_weapon()
	_render_trace()

func _sample_weapon() -> void:
	var root_world := _weapon.global_transform.origin
	var tip_world := _weapon.global_transform * (_tip_local)
	_short_points.push_front({"age": 0.0, "pos": root_world})
	_long_points.push_front({"age": 0.0, "pos": tip_world})
	_trim_expired()

func _age_points(delta: float) -> void:
	for sample in _short_points:
		sample["age"] = float(sample.get("age", 0.0)) + delta
	for sample in _long_points:
		sample["age"] = float(sample.get("age", 0.0)) + delta
	_trim_expired()

func _trim_expired() -> void:
	while not _short_points.is_empty() and float(_short_points.back().get("age", 0.0)) > lifetime:
		_short_points.pop_back()
	while not _long_points.is_empty() and float(_long_points.back().get("age", 0.0)) > lifetime:
		_long_points.pop_back()

func clear() -> void:
	_short_points.clear()
	_long_points.clear()
	_vertex_count = 0
	if is_instance_valid(_mesh):
		_mesh.clear_surfaces()
	if is_instance_valid(_mesh_instance):
		_mesh_instance.visible = false

func _resolve_tip_local() -> bool:
	# CWeaponTrace::SetWeaponInstance computes m_fLength from the maximum
	# distance between the weapon bone origin and GetBoundBox() corners. It does
	# not select that corner as the direction of the blade. Update() then moves
	# along the composite bone's local Z axis by m_fLength * reach_scale.
	var inverse := _weapon.global_transform.affine_inverse()
	var farthest := 0.0
	var meshes: Array[MeshInstance3D] = []
	if _weapon is MeshInstance3D:
		meshes.append(_weapon as MeshInstance3D)
	for child in _weapon.find_children("*", "MeshInstance3D", true, false):
		var mi := child as MeshInstance3D
		if mi != null and not meshes.has(mi):
			meshes.append(mi)
	for mi in meshes:
		if mi.mesh == null:
			continue
		var box := mi.get_aabb()
		for corner in 8:
			var local_point := box.position + Vector3(
				box.size.x if (corner & 1) != 0 else 0.0,
				box.size.y if (corner & 2) != 0 else 0.0,
				box.size.z if (corner & 4) != 0 else 0.0)
			var world_point: Vector3 = mi.global_transform * local_point
			var weapon_local: Vector3 = inverse * world_point
			var distance := weapon_local.length_squared()
			if distance > farthest:
				farthest = distance
	if farthest <= 0.000001 or is_zero_approx(reach_scale):
		return false
	_tip_local = Vector3(0.0, 0.0, sqrt(farthest) * reach_scale)
	return _tip_local.length_squared() > 0.000001

func _render_trace() -> void:
	if _short_points.size() <= 1 or _long_points.size() <= 1:
		_vertex_count = 0
		_mesh.clear_surfaces()
		_mesh_instance.visible = false
		return
	var vertices := _build_vertices()
	_vertex_count = vertices.size()
	_mesh.clear_surfaces()
	if vertices.size() < 4:
		_mesh_instance.visible = false
		return
	_mesh.surface_begin(Mesh.PRIMITIVE_TRIANGLE_STRIP, _material)
	for vertex in vertices:
		_mesh.surface_set_color(Color(TRACE_COLOR.r, TRACE_COLOR.g, TRACE_COLOR.b,
				float(vertex.get("alpha", 0.0))))
		_mesh.surface_set_uv(vertex.get("uv", Vector2.ZERO))
		_mesh.surface_add_vertex(to_local(vertex.get("pos", Vector3.ZERO)))
	_mesh.surface_end()
	_mesh_instance.visible = true

func _build_vertices() -> Array:
	var length := minf(lifetime, float(_long_points.back().get("age", 0.0)))
	var out: Array = []
	# Reference BuildVertex renders the long track first (UV y=0), then the
	# short track (UV y=1), interleaving the pair into a triangle strip.
	var long_vertices := _build_spline(_long_points, true, length)
	var short_vertices := _build_spline(_short_points, false, length)
	var count := mini(long_vertices.size(), short_vertices.size())
	for i in count:
		out.append(long_vertices[i])
		out.append(short_vertices[i])
	return out

func _build_spline(input: Array, is_long: bool, length: float) -> Array:
	var out: Array = []
	var n := input.size() - 1
	if n <= 0:
		return out
	var h: Array = []
	var r: Array = []
	h.resize(n + 1)
	r.resize(n + 1)
	for i in n:
		var dt := float(input[i + 1].get("age", 0.0)) - float(input[i].get("age", 0.0))
		if dt <= 0.000001:
			return out
		h[i] = dt
		var p0: Vector3 = input[i].get("pos", Vector3.ZERO)
		var p1: Vector3 = input[i + 1].get("pos", Vector3.ZERO)
		r[i] = (p1 - p0) * (3.0 / dt)
	r[n] = Vector3.ZERO
	for i in range(n, 0, -1):
		r[i] = r[i] + r[i - 1]
	var stack: Array = []
	var rate := 0.5
	r[0] = r[0] * 0.5
	stack.append(rate)
	for i in range(1, n):
		r[i] = r[i] - r[i - 1]
		rate = 1.0 / (4.0 - rate)
		r[i] = r[i] * rate
		stack.append(rate)
	r[n] = r[n] - r[n - 1]
	rate = 1.0 / (2.0 - rate)
	r[n] = r[n] * rate
	for i in range(n - 1, -1, -1):
		r[i] = r[i] - float(stack.pop_back()) * r[i + 1]

	var base := 0
	var timebase := 0.0
	var timenext := float(h[0])
	var delta := maxf(sampling_time, 0.0001)
	var a: Vector3 = input[0].get("pos", Vector3.ZERO)
	var b: Vector3 = r[0]
	var first_delta: Vector3 = input[1].get("pos", Vector3.ZERO) - a
	var c: Vector3 = (3.0 * first_delta - r[1] * float(h[0]) - 2.0 * float(h[0]) * r[0]) \
			/ (float(h[0]) * float(h[0]))
	var d: Vector3 = (-2.0 * first_delta + (r[1] + r[0]) * float(h[0])) \
			/ (float(h[0]) * float(h[0]) * float(h[0]))
	var t := 0.0
	var life := maxf(lifetime, 0.001)
	while t <= length + 0.000001:
		while t > timenext and base < n:
			timebase = timenext
			base += 1
			if base >= n:
				break
			var seg_delta: Vector3 = input[base + 1].get("pos", Vector3.ZERO) - input[base].get("pos", Vector3.ZERO)
			a = input[base].get("pos", Vector3.ZERO)
			b = r[base]
			c = (3.0 * seg_delta - r[base + 1] * float(h[base]) -
					2.0 * float(h[base]) * r[base]) / (float(h[base]) * float(h[base]))
			d = (-2.0 * seg_delta + (r[base + 1] + r[base]) * float(h[base])) / \
					(float(h[base]) * float(h[base]) * float(h[base]))
			timenext += float(h[base])
		if base >= n:
			break
		var cc := t - timebase
		var position: Vector3 = a + cc * (b + cc * (c + cc * d))
		var ttt := clampf((t + float(input[0].get("age", 0.0))) / life, 0.0, 1.0)
		var alpha := clampf((1.0 - ttt) * (1.0 - ttt) / 2.5 - 0.1, 0.0, 1.0) if is_long else 0.0
		out.append({"pos": position, "uv": Vector2(t / life, 0.0 if is_long else 1.0), "alpha": alpha})
		t += delta
	return out

func _load_texture(path: String) -> Texture2D:
	if path == "":
		return null
	if ResourceLoader.exists(path):
		return ResourceLoader.load(path) as Texture2D
	if not FileAccess.file_exists(path):
		return null
	var image := Image.load_from_file(path)
	return ImageTexture.create_from_image(image) if image != null and not image.is_empty() else null