neon-sprawl/docs/plans/NEON-2-implementation-plan.md

NEON-2 — Implementation plan

Story reference

Field	Value
Key	NEON-2
Title	E1.M1: Click-to-move prototype (client-only)
Jira	NEON-2
Parent context	NEON-9 — E1.M1 InputAndMovementRuntime

Goal, scope, and out-of-scope

Goal: On the Godot client only, prove click-to-move locomotion and the input → world-target path before any networking or server authority.

In scope

• Placeholder avatar in the prototype scene (main.tscn or a dedicated movement test scene; default choice: extend main.tscn so F5 still runs the prototype).
• Ground pick via camera raycast; on valid hit, command movement to that point.
• Flat prototype terrain and simple obstacles sufficient to validate stopping behavior.
• Brief note in README and/or scene that this is temporary until authoritative movement sync exists.

Out of scope (per Jira)

• Game server, persistence, MoveCommand / wire protocol, Protobuf contracts.

Acceptance criteria checklist

• Clicking walkable ground moves the avatar to the destination without requiring WASD (mouse-only locomotion for this prototype).
• Movement stops at obstacles when using navigation; or if using a direct move-to approach instead, the limitation is documented (README and/or plan).
• README or an in-editor scene note states this behavior is provisional until authoritative sync lands.

Technical approach

1. Scene setup (main.tscn)

   • Add a Camera3D suitable for ground picking (angled downward at a StaticBody3D floor with collision).
   • Add a CharacterBody3D placeholder (e.g. CapsuleMesh + CollisionShape3D) as the avatar.
   • Add at least one obstacle (StaticBody3D) so “stop at obstacles” is observable.
   • Add a NavigationRegion3D covering the walkable floor; bake a navigation mesh from the floor (and subtract or exclude obstacles per Godot 4 workflow).

2. Movement model

   • Prefer NavigationAgent3D on the avatar: set target_position from the raycast hit on the ground; each frame move the body toward the agent’s next path position (e.g. velocity + move_and_slide, or equivalent Godot 4 pattern). This satisfies the AC path that expects stopping at obstacles via navigation.
   • Fallback only if navigation proves unnecessarily heavy for the first slice: direct move_toward / velocity toward the click point with move_and_slide and document that there is no pathfinding.

3. Input

   • _unhandled_input or _input: on left mouse button, raycast from camera through cursor into the physics world; if the collider is the ground (or a dedicated “walkable” layer/mask), set the navigation target.

4. Documentation

   • Update client/README.md with a short “Movement prototype (NEON-2)” subsection: mouse click-to-move, navigation-based obstacle avoidance, not server-authoritative.
   • Optional: Editable Children note on root node in scene or a comment in main.gd pointing to NEON-2 / temporariness.

Files to add

Path	Purpose
None required initially	If main.gd grows unwieldy, optionally extract scripts/player_navigation.gd (or similar) attached to the avatar—only if it keeps the scene readable.

(Default: implement in existing scripts/main.gd + scene edits unless script size forces a split.)

Files to modify

Path	Rationale
client/scenes/main.tscn	Add camera, terrain, obstacles, navigation region, avatar, and wire scripts.
client/scripts/main.gd	Raycast-on-click, navigation target updates, and any per-frame movement driver if kept on root.
client/README.md	Document prototype movement, temporary nature, and manual verification steps.
client/project.godot	Only if needed (e.g. input map, layer names, or feature flags)—prefer minimal diffs.

Tests

• Automated: None for this story; the repo has no Godot test harness yet (testing expectations).
• Manual verification:
  1. Open client/ in Godot 4.2+, run main scene.
  2. Click on the floor: avatar moves to the point without using WASD.
  3. Click a destination behind an obstacle: avatar path avoids or stops appropriately per navigation behavior.
  4. Confirm README/scene note mentions provisional client-only movement.

Open questions / risks

• Navigation baking: First-time contributors need to bake the navigation mesh in the editor after pulling scene changes; document that in README if it is not obvious.
• Isometric later: Camera rig may be replaced for isometric; keep movement logic independent of camera style where possible (raycast from current camera).
• Performance: Single-agent prototype is sufficient; no need to optimize for crowds in NEON-2.