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RTS Mass Army & Fog Deep-Dive (load on demand)

LLM-ignorance keep rule: content here is expert Godot/genre knowledge a general agent would not know without reading — never delete, only relocate.

MANDATORY when implementing systems beyond the scripts/ catalog. Peer skills own full tutorials — route after this reference.

Architecture Overview

1. Selection Manager (Singleton or Commander Node)

Handles mouse input for selecting units.

# selection_manager.gd
extends Node2D

var selected_units: Array[Unit] = []
var drag_start: Vector2
var is_dragging: bool = false
@onready var selection_box: Panel = $SelectionBox

func _unhandled_input(event):
    if event is InputEventMouseButton and event.button_index == MOUSE_BUTTON_LEFT:
        if event.pressed:
            start_selection(event.position)
        else:
            end_selection(event.position)
    elif event is InputEventMouseMotion and is_dragging:
        update_selection_box(event.position)

func end_selection(end_pos: Vector2):
    is_dragging = false
    selection_box.visible = false
    var rect = Rect2(drag_start, end_pos - drag_start).abs()
    
    if Input.is_key_pressed(KEY_SHIFT):
        # Add to selection
        pass
    else:
        deselect_all()
        
    # Query physics server for units in rect
    var query = PhysicsShapeQueryParameters2D.new()
    var shape = RectangleShape2D.new()
    shape.size = rect.size
    query.shape = shape
    query.transform = Transform2D(0, rect.get_center())
    # ... execute query and add units to selected_units
    
    for unit in selected_units:
        unit.set_selected(true)

func issue_command(target_position: Vector2):
    for unit in selected_units:
        unit.move_to(target_position)

2. Unit Controller (State Machine)

Units need robust state management to handle commands and auto-attacks.

# unit.gd
extends CharacterBody2D
class_name Unit

enum State { IDLE, MOVE, ATTACK, HOLD }
var state: State = State.IDLE
var command_queue: Array[Command] = []

@onready var nav_agent: NavigationAgent2D = $NavigationAgent2D

func move_to(target: Vector2):
    nav_agent.target_position = target
    state = State.MOVE

func _physics_process(delta):
    if state == State.MOVE:
        if nav_agent.is_navigation_finished():
            state = State.IDLE
            return
            
        var next_pos = nav_agent.get_next_path_position()
        var direction = global_position.direction_to(next_pos)
        velocity = direction * speed
        move_and_slide()

### 3. Group Movement & Flocking
Instead of moving all units directly to a single point (clumping), use **Relative Offsets**:
- Calculate the **Center of Mass** for the selected group.
- On click, calculate each unit's **Relative Offset** from the center.
- Issue `target_position + unit_offset` to each unit to maintain formation.

3. Fog of War

A system to hide unvisited areas. Usually implemented with a texture and a shader.

• Grid Approach: 2D array of "visibility" values.
• Viewport Texture: A SubViewport drawing white circles for units on a black background. This texture is then used as a mask in a shader on a full-screen ColorRect overlay.

shader_type canvas_item;
uniform sampler2D visibility_texture; 
uniform vec4 fog_color : source_color;

void fragment() {
    float visibility = texture(visibility_texture, UV).r;
    COLOR = mix(fog_color, vec4(0,0,0,0), visibility);
}

Key Mechanics Implementation

Command Queue

Allow players to chain commands (Shift-Click).

• Implementation: Store commands in an Array. When one finishes, pop the next.
• Visuals: Draw lines showing the queued path.

Resource Gathering

• Nodes: ResourceNode (Tree/GoldMine) and DropoffPoint (TownCenter).
• Logic:
  1. Move to Resource.
  2. Work (Timer).
  3. Move to Dropoff.
  4. Deposit (Global Economy update).
  5. Repeat.

Godot-Specific Tips

• Avoidance: NavigationAgent2D has built-in RVO avoidance. Make sure to call set_velocity() and use the velocity_computed signal for the actual movement!
• Server Architecture: For 100+ units, don't use _process on every unit. Have a central UnitManager iterate through active units to save function call overhead.
• Groups: Use Groups heavily (Units, Buildings, Resources) for easy selection filters.

🚀 Elite Technical Implementations (Batch 09)

1. Center-of-Mass Formation Movement Pattern

To prevent CPU bottlenecks when moving hundreds of units, avoid querying individual paths. Instead, calculate the "Center of Mass" of the selection and perform a single NavigationServer3D (or 2D) path query.

class_name RTSFormationManager extends Node

---

## Moves a group of units in formation to a target destination using a single path query.
static func move_group_to_target(units: Array[CharacterBody3D], target_position: Vector3, map_rid: RID) -> void:
    if units.is_empty():
        return
        
    # 1. Calculate the Center of Mass (Average Position)
    var center_of_mass := Vector3.ZERO
    for unit in units:
        center_of_mass += unit.global_position
    center_of_mass /= units.size()
    
    # 2. Query NavigationServer for the optimized central path
    var central_path: PackedVector3Array = NavigationServer3D.map_get_path(
        map_rid,
        center_of_mass,
        target_position,
        true 
    )
    
    if central_path.is_empty():
        return
        
    var final_center_destination: Vector3 = central_path[central_path.size() - 1]
    
    # 3. Distribute commands with relative offsets to maintain formation
    for unit in units:
        var offset: Vector3 = unit.global_position - center_of_mass
        var unit_destination: Vector3 = final_center_destination + offset
        
        if unit.has_method("set_movement_target"):
            unit.set_movement_target(unit_destination)

2. MultiMeshInstance Rendering for Massive Armies

Standard nodes fail when unit counts reach thousands. Use MultiMeshInstance3D to draw millions of objects in a single draw call via the GPU.

• Architectural Tip: Pre-allocate the maximum expected units and toggle visibility via visible_instance_count.
• Performance: Note that individual frustum culling is disabled for MultiMesh instances; the entire group is either drawn or not.

class_name RTSMassiveUnitRenderer extends MultiMeshInstance3D

@export var max_units: int = 10000
@export var unit_mesh: Mesh

func _ready() -> void:
    multimesh = MultiMesh.new()
    multimesh.transform_format = MultiMesh.TRANSFORM_3D
    multimesh.use_colors = true 
    multimesh.instance_count = max_units
    multimesh.mesh = unit_mesh
    multimesh.visible_instance_count = 0

---

## Sync logical unit transforms to GPU instances
func synchronize_rendering(active_units: Array[Transform3D]) -> void:
    var count: int = min(active_units.size(), max_units)
    multimesh.visible_instance_count = count
    
    for i in range(count):
        multimesh.set_instance_transform(i, active_units[i])

3. SubViewport Fog-of-War System

Avoid complex geometry. Use a SubViewport as a dynamic render target to generate a vision mask (White = Vision, Black = Fog).

Mask Generator Logic:

class_name FogOfWarManager extends SubViewport

@export var terrain_material: ShaderMaterial
@export var world_bounds: Vector2 = Vector2(1024, 1024)

func _ready() -> void:
    disable_3d = true 
    render_target_update_mode = SubViewport.UPDATE_ALWAYS
    
    await RenderingServer.frame_post_draw 
    var fow_texture: ViewportTexture = get_texture()
    terrain_material.set_shader_parameter("fow_mask", fow_texture)
    terrain_material.set_shader_parameter("world_bounds", world_bounds)

Projection Shader (Spatial):

shader_type spatial;
uniform sampler2D fow_mask : hint_default_black, filter_linear;
uniform vec2 world_bounds;
uniform vec3 fog_color : source_color = vec3(0.1, 0.1, 0.15);

void fragment() {
    // Map World X/Z to 2D UV Coordinates
    vec2 fow_uv = (NODE_POSITION_WORLD.xz / world_bounds) + vec2(0.5);
    float visibility = texture(fow_mask, fow_uv).r;
    
    ALBEDO = mix(fog_color, ALBEDO, visibility);
}

• Master Skill: godot-master