standalone TrailRender Godot4 port

TrailRenderScriptClass/TrailRendererGodot4.gd

@@ -0,0 +1,125 @@
+extends Node3D
+class_name TrailRenderer
+
+#############################
+# EXPORT PARAMS
+#############################
+# width
+@export var width: float = 0.5
+@export var width_curve: Curve
+# length
+@export var max_points := 100
+@export var material: Material
+# show or hide
+@export var render: bool = true
+
+
+#############################
+# PARAMS
+#############################
+@onready var half_width = width * 0.5
+var points := []
+
+
+#############################
+# OVERRIDE FUNCTIONS
+#############################
+func _ready() -> void:
+	var node = Node.new()
+	node.name = "Node"
+	add_child(node)
+
+	var render = MeshInstance3D.new()
+	render.name = "Render"
+	node.add_child(render)
+
+
+func _process(delta: float) -> void:
+	if render:
+		# add new point and render
+		add_point()
+		_draw_trail()
+	else:
+		# slowly hide the trail
+		if points.size() > 0:
+			var last_point = points.pop_back()
+			last_point.queue_free()
+
+
+#############################
+# API
+#############################
+func add_point() -> void:
+	var new_point = Position3D.new()
+	new_point.position = self.global_transform.origin
+	new_point.rotation = self.global_transform.basis.get_euler()
+	points.insert(0, new_point)
+	if points.size() > max_points:
+		var last_point = points.pop_back()
+		last_point.queue_free()
+
+
+func _draw_trail() -> void:
+	if points.size() < 2:
+		return
+	# create surface tool
+	var st = SurfaceTool.new()
+	st.begin(Mesh.PRIMITIVE_TRIANGLES)
+	# draw triangles
+	for i in range(points.size() - 1):
+		_points_to_rect(st, points[i], points[i + 1], i)
+	# commit
+	st.generate_normals()
+#	st.generate_tangents()
+	$Node/Render.mesh = st.commit()
+	$Node/Render.set_surface_override_material(0, material)
+
+
+func _points_to_rect(st: SurfaceTool, p1: Position3D, p2: Position3D, idx: float) -> void:
+	var num_points = points.size() - 1
+
+	var offset1 = idx / num_points
+	var mod1 = half_width * width_curve.interpolate(offset1)
+
+	var v1 = p1.position + p1.transform.basis.x * mod1
+	var uv1 = Vector2(0, offset1)
+
+	var v2 = p1.position - p1.transform.basis.x * mod1
+	var uv2 = Vector2(1, offset1)
+
+	var offset2 = (idx + 1) / num_points
+	var mod2 = half_width * width_curve.interpolate(offset2)
+
+	var v3 = p2.position + p2.transform.basis.x * mod2
+	var uv3 = Vector2(0, offset2)
+
+	var v4 = p2.position - p2.transform.basis.x * mod2
+	var uv4 = Vector2(1, offset2)
+
+	st.set_uv(uv1)
+	st.add_vertex(v1)
+	st.set_uv(uv2)
+	st.add_vertex(v2)
+	st.set_uv(uv3)
+	st.add_vertex(v3)
+
+	st.set_uv(uv3)
+	st.add_vertex(v3)
+	st.set_uv(uv2)
+	st.add_vertex(v2)
+	st.set_uv(uv1)
+	st.add_vertex(v1)
+
+	st.set_uv(uv3)
+	st.add_vertex(v3)
+	st.set_uv(uv4)
+	st.add_vertex(v4)
+	st.set_uv(uv2)
+	st.add_vertex(v2)
+
+	st.set_uv(uv2)
+	st.add_vertex(v2)
+	st.set_uv(uv4)
+	st.add_vertex(v4)
+	st.set_uv(uv3)
+	st.add_vertex(v3)