✨ Projectile trail for the spacegun

weapons/space_gun/projectile.tscn

@@ -1,7 +1,15 @@
-[gd_scene load_steps=5 format=3 uid="uid://dn1tcakam5egs"]
+[gd_scene load_steps=7 format=3 uid="uid://dn1tcakam5egs"]
 
 [ext_resource type="Script" path="res://weapons/space_gun/projectile.gd" id="1_4j1dp"]
 [ext_resource type="PackedScene" uid="uid://8atq41j7wd55" path="res://weapons/space_gun/projectile_explosion.tscn" id="2_llml6"]
+[ext_resource type="Script" path="res://weapons/space_gun/projectile_trail.gd" id="3_ygqbh"]
+
+[sub_resource type="StandardMaterial3D" id="StandardMaterial3D_4a265"]
+transparency = 1
+blend_mode = 1
+cull_mode = 2
+shading_mode = 0
+vertex_color_use_as_albedo = true
 
 [sub_resource type="StandardMaterial3D" id="StandardMaterial3D_o6j55"]
 albedo_color = Color(0, 0.498039, 0.854902, 1)
@@ -15,6 +23,15 @@ radius = 0.15
 script = ExtResource("1_4j1dp")
 EXPLOSION = ExtResource("2_llml6")
 
+[node name="Trail3D" type="MeshInstance3D" parent="."]
+material_override = SubResource("StandardMaterial3D_4a265")
+script = ExtResource("3_ygqbh")
+_from_width = 0.15
+_scale_acceleration = 0.5
+_lifespan = 0.25
+_start_color = Color(0, 0.498039, 0.854902, 1)
+_end_color = Color(1, 1, 1, 0)
+
 [node name="Mesh" type="CSGSphere3D" parent="."]
 transform = Transform3D(1, 0, 0, 0, 0.2, 0, 0, 0, 1, 0, 0, 0)
 radius = 0.15

weapons/space_gun/projectile_trail.gd

@@ -0,0 +1,80 @@
+class_name Trail3D extends MeshInstance3D
+
+var _points = [] # 3D points of trail
+var _widths = [] # Calculated widths of trail
+var _lifespans = [] # Trail point lifespans
+
+@export var _trail_enabled : bool = true # Is trail shown?
+
+@export var _from_width : float = 0.5 # Starting width
+@export var _to_width : float = 0.0 # Ending width
+
+@export_range(0.5, 1.5) var _scale_acceleration : float = 1.0 # Scaling speed
+
+@export var _motion_delta : float = 0.1 # Smoothness of trail
+@export var _lifespan : float = 1.0 # Duration of trail
+
+@export var _start_color : Color = Color(1.0, 1.0, 1.0, 1.0) # Start color
+@export var _end_color : Color = Color(1.0, 1.0, 1.0, 1.0) # End color
+
+var _old_pos : Vector3 # Previous pos
+
+func _append_point():
+	_points.append(get_global_transform().origin)
+	_widths.append([
+		get_global_transform().basis.x * _from_width,
+		get_global_transform().basis.x * _from_width - get_global_transform().basis.x * _to_width
+	])
+	_lifespans.append(0.0)
+
+func _remove_point(i):
+	_points.remove_at(i)
+	_widths.remove_at(i)
+	_lifespans.remove_at(i)
+
+func _ready():
+	_old_pos = get_global_transform().origin
+	mesh = ImmediateMesh.new()
+
+func _process(delta):
+	if(_old_pos - get_global_transform().origin).length() > _motion_delta and _trail_enabled:
+		_append_point() # Create new point
+		_old_pos = get_global_transform().origin # Update previous position to current position coordinates
+		
+	# Update the lifespan
+	var p = 0
+	var max_points = _points.size()
+	while p < max_points:
+		_lifespans[p] += delta
+		if _lifespans[p] > _lifespan:
+			_remove_point(p)
+			p -= 1
+			if (p < 0): p = 0
+		
+		max_points = _points.size()
+		p += 1
+		
+	mesh.clear_surfaces()
+	
+	# If less than 2 points, stop rendering trail
+	if _points.size() < 2:
+		return
+	
+	# Render new mesh for each point
+	mesh.surface_begin(Mesh.PRIMITIVE_TRIANGLE_STRIP)
+	
+	for i in range(_points.size()):
+		var t = float(i) / (_points.size() - 1.0)
+		var curr_color = _start_color.lerp(_end_color, 1 - t)
+		mesh.surface_set_color(curr_color)
+		
+		var curr_width = _widths[i][0] - pow(1 - t, _scale_acceleration) * _widths[i][1]
+		
+		var t0 = i / _points.size()
+		var t1 = t
+		
+		mesh.surface_set_uv(Vector2(t0, 0))
+		mesh.surface_add_vertex(to_local(_points[i] + curr_width))
+		mesh.surface_set_uv(Vector2(t1, 1))
+		mesh.surface_add_vertex(to_local(_points[i] - curr_width))
+	mesh.surface_end()