Skill v1.0.2

version: "1.0.2" name: godot-adapt-3d-to-2d description: "Expert patterns for simplifying 3D games to 2D including dimension reduction strategies, 2.5D fake-depth, isometric ports, camera flattening, physics conversion, 3D-to-sprite art pipeline, and control simplification. Use when porting 3D to 2D, building 2.5D / isometric / fake-depth gameplay, creating 2D versions for mobile, or prototyping. Trigger keywords: CharacterBody3D to CharacterBody2D, Camera3D to Camera2D, Vector3 to Vector2, flatten Z-axis, 2.5D, isometric, fake depth, Y-sort, simulated Z, orthogonal projection, 3D to sprite conversion, performance optimization."

NEVER Do

• NEVER remove Z-axis without gameplay compensation — Blindly flattening 3D to 2D removes spatial strategy. Add other depth mechanics (layers, jump height variations).
• NEVER keep 3D collision shapes — Use simpler 2D shapes (CapsuleShape2D, RectangleShape2D). 3D shapes don't convert automatically.
• NEVER use orthographic Camera3D as "2D mode" — WHY: You still pay 3D transform/lighting costs and miss CanvasItem batching. Use Camera2D + 2D nodes (`ortho_simulation.gd` only for simulated height).
• NEVER assume automatic performance gain — Poorly optimized 2D (too many draw calls, large sprite sheets) can be slower than optimized 3D.
• NEVER forget to adjust gravity — 3D gravity is Vector3(0, -9.8, 0). 2D gravity is float (980 pixels/s²). Scale appropriately.
• NEVER treat ground and air hits as the same Area2D overlap — In 2.5D, a ground slash must not hit jumping targets. WHY: 2D physics has no Z. Use `hitbox_depth_manager.gd` height AABB checks.
• NEVER fight Y-sort with per-sprite `z_index` spam — WHY: Ownership of sort order belongs on the Y-sorted parent. Use `depth_sorting_y_sort.gd`; manual z_index drifts every frame.

Available Scripts

MANDATORY: Read the appropriate script before implementing the corresponding pattern.

Strategy router (MANDATORY / Do NOT Load)

ortho_simulation.gd

Simulates 3D Z-axis height in 2D top-down games. Handles vertical velocity, gravity, sprite offset, and shadow scaling.

projection_utils.gd

Projects 3D world positions to 2D screen space for nameplates, healthbars, and targeting. Handles behind-camera detection and distance-based scaling.

isometric_math_core.gd

Expert utility generating translating between 2D Cartesian and True Isometric screenspace projection matrices without using 2D Node transforms.

depth_sorting_y_sort.gd

Expert dynamic Z-index Y-Sort script for fake 3D sorting isolated trees matching CanvasItem _update_sorting().

jump_z_axis_sim.gd

Complete CharacterBody2D snippet separating structural physical ground movement (X,Y) from a mathematically simulated jumping height (Z) in a topdown game.

parallax_depth_camera.gd

Fake Depth Camera applying varying offset algorithms to completely disparate CanvasLayers based on an index to simulate 3D camera translation panning.

hitbox_depth_manager.gd

Area2D derived class that requires explicit custom Z-height overlap (1D AABB collision) prior to validating 2D triggers to stop incorrect "ground vs air" collision in 2.5D.

fake_3d_shadows.gd

Sprite2D shadow simulator exploiting Godot 4.x Transform2D matrix skew shear to project and angle shadows away from a simulated 3D sun direction on a 2D floor.

billboard_sprite_manager.gd

8-directional FPS Doom-style sprite controller isolating the simulated 3D relative angle between a moving 2D CharacterBody and a Camera2D viewpoint.

nav_region_flattening.gd

Topdown 2D pathfinding workaround allowing "aerial" units to cross walls by leveraging multiple tiered 2D Navigation Layers instead of proper 3D verticality.

ortho_to_perspective_fx.gd

Screen space CanvasItem warp Shader simulating a Mode 7 / tabletop perspective pitch. Maps top screen coordinates via division pinching.

2d_lighting_normals.gd

Automatic programmatic generation of CanvasTexture combining base albedo and baked normal maps at runtime so Sprites correctly react to 2D PointLIGHTs like 3D geometry.

model_to_sprite_bake.gd

MANDATORY for automated 3D→sprite angle baking via SubViewport. Keep body as strategy router.

grid_nav_bridge.gd

Flatten 3D nav intent onto AStarGrid2D for grid-based 2D ports (XZ → cell indices).

Dimension Reduction Strategies

Pick one row from the strategy router above — do not paste conversion tutorials in-scene.

Gravity scale: 3D 9.8 m/s² → 2D ~980 px/s² when 1 m ≈ 100 px. Collisions: CapsuleShape3D → CapsuleShape2D (see Physics Adjustments). Camera: Camera3D/SpringArm → Camera2D — NEVER ortho Camera3D as “2D mode”.

Art Pipeline: 3D Models → Sprites

MANDATORY when baking multi-angle sprites from GLB/scenes: `model_to_sprite_bake.gd` (@tool SubViewport baker). Manual Blender export stays outside this skill. Strategy choice stays in the decision tree below — do not re-inline bake recipes in the body.

Physics Adjustments

Gravity Scaling

# 3D gravity (m/s²): 9.8
# 2D gravity (pixels/s²): Scale to pixel units
 
# If 1 meter = 100 pixels:
const GRAVITY_2D = 9.8 * 100  # = 980 pixels/s²
 
# Adjust jump velocity proportionally:
# 3D jump: 4.5 m/s
# 2D jump: -450 pixels/s

Collision Simplification

# 3D: CapsuleShape3D (16 segments, expensive)
var shape_3d := CapsuleShape3D.new()
shape_3d.radius = 0.5
shape_3d.height = 2.0
 
# 2D: CapsuleShape2D (much simpler)
var shape_2d := CapsuleShape2D.new()
shape_2d.radius = 16  # pixels
shape_2d.height = 64

Control Simplification

3D Free Movement → 2D Restricted

# 3D: Full 3D movement with camera-relative controls
var input_3d := Input.get_vector("left", "right", "forward", "back")
var camera_basis := camera.global_transform.basis
var direction := (camera_basis * Vector3(input_3d.x, 0, input_3d.y)).normalized()
 
# 2D: Simple 4-direction (or 8-direction with diagonals)
var input_2d := Input.get_vector("left", "right", "up", "down")
velocity = input_2d.normalized() * SPEED

Performance Gains

Optimization Techniques

# 1. Use TileMapLayer instead of individual Sprite2D nodes
var tilemap := TileMapLayer.new()
tilemap.tile_set = load("res://tileset.tres")
 
# 2. Batch sprite rendering
# Use single large sprite sheet instead of individual textures
 
# 3. Reduce particle count
var godot-particles := GPUParticles2D.new()
godot-particles.amount = 50  # Down from 200 in 3D

UI Adaptation

# Most 3D games already use 2D UI (CanvasLayer)
# No changes needed!
 
# Just verify UI scaling for new aspect ratios
get_viewport().size_changed.connect(_on_viewport_resized)
 
func _on_viewport_resized() -> void:
    var viewport_size := get_viewport().get_visible_rect().size
    # Adjust UI anchors/margins

Edge Cases

Depth Sorting

NEVER drive sort with per-sprite z_index = int(global_position.y) — that contradicts Y-sort ownership. MANDATORY `depth_sorting_y_sort.gd`: enable y_sort_enabled on the parent and keep children at default relative z.

Lost Spatial Audio

# 3D spatial audio (AudioStreamPlayer3D) → 2D panning (AudioStreamPlayer2D)
 
var audio_2d := AudioStreamPlayer2D.new()
audio_2d.stream = load("res://sounds/footstep.ogg")
audio_2d.max_distance = 1000.0  # 2D range
audio_2d.attenuation = 2.0
add_child(audio_2d)

Decision Tree: When to Simplify to 2D

Expert Techniques & Optimizations

1. Flattened Navigation (3D Navmesh to 2D Grid)

While Godot treats 2D and 3D navigation as separate systems, you can project 3D pathfinding logic onto a 2D grid using AStarGrid2D. This is highly optimized for 2D grid-based movement and avoids the overhead of a full 3D navmesh.

class_name GridNavBridge extends Node
 
var astar_grid: AStarGrid2D
 
func _ready() -> void:
    astar_grid = AStarGrid2D.new()
    astar_grid.region = Rect2i(0, 0, 100, 100)
    astar_grid.cell_size = Vector2(16, 16)
    astar_grid.update()
 
## Converts a 3D target position to a 2D grid path.
func get_grid_path_from_3d(start_3d: Vector3, end_3d: Vector3) -> PackedVector2Array:
    var start_map := Vector2i(start_3d.x / 16, start_3d.z / 16)
    var end_map := Vector2i(end_3d.x / 16, end_3d.z / 16)
    
    return astar_grid.get_point_path(start_map, end_map)

2. Auto-LOD for 2D (Performance Optimization)

Automatic LOD is natively a 3D feature, but you can simulate it in 2D using VisibleOnScreenEnabler2D. This node automatically toggles the process_mode of target nodes (like high-res sprites or complex AI) when they leave the screen, preserving CPU cycles and GPU fill rate.

# Attach to a complex 2D entity
func setup_2d_lod(target_node: Node2D) -> void:
    var enabler := VisibleOnScreenEnabler2D.new()
    # Define the 'high-detail' rect
    enabler.rect = Rect2(-64, -64, 128, 128) 
    enabler.enable_node_path = target_node.get_path()
    add_child(enabler)

3. Dimensional Patcher (CharacterBody3D to 2D Regex)

To automate the down-porting of 3D controllers, use a RegEx script to map Vector3 to Vector2 and replace 3D-specific properties. This is essential for massive porting tasks where manual conversion of movement logic is prone to error.

@tool
extends EditorScript
 
func _run() -> void:
    var regex = RegEx.new()
    # Pattern to find Vector3 constructors and replace with Vector2
    regex.compile("Vector3\\(([^,]+),\\s*([^,]+),\\s*([^)]+)\\)")
    
    var script_content = "velocity = Vector3(input.x, 0.0, input.y) * speed"
    var result = regex.sub(script_content, "Vector2($1, $3)", true)
    
    # Output: "velocity = Vector2(input.x, input.y) * speed"
    print(result)

Deep recipes (on demand)

Reference

Progressive disclosure: open Official Documentation links only when researching a specific API; load Related Skills when routing to a peer domain — do not preload the whole lattice.

Official Documentation

• Introduction to 2D — Establishes the CanvasItem/Camera2D pipeline you must switch into when leaving Node3D rendering for real 2D performance.
• Using CharacterBody2D — Canonical move_and_slide / floor / jump patterns after CharacterBody3D → CharacterBody2D conversion.
• Physics introduction — Units, layers/masks, and why 3D gravity/Vector3 assumptions break when gravity becomes a 2D scalar.
• 2D transforms — Transform2D basis/skew math used for isometric placement and fake projected shadows.
• 2D parallax — Layer scroll scales that replace Z-depth when gameplay collapses to a plane.
• Canvas layers — Stacking CanvasLayers for fake-depth cameras without keeping an orthographic Camera3D.
• 2D lights and shadows — Normal-mapped CanvasTexture / Light2D path that restores 3D-looking lighting on sprites.
• Navigation introduction (2D) — 2D nav regions/layers for flattening vertical 3D pathing into tiered 2D agents.
• Using Viewports — SubViewport capture of 3D models into Sprite2D textures (runtime or bake pipeline).
• Camera2D — Zoom, limits, and follow API that should replace “ortho Camera3D as 2D mode.”
• CanvasItem — y_sort_enabled / z_index / z_as_relative for depth sorting after losing true Z.
• General optimization — Reminds that 2D only wins if draw calls, overdraw, and process cost are actually reduced.

Related Skills

Prerequisites

• godot-characterbody-2d — Destination movement API for top-down/platformer ports once Z is simulated or removed.
• godot-2d-physics — CapsuleShape2D/Area2D collision simplification and layer masks after dropping 3D shapes.
• godot-camera-systems — Camera2D follow/limits/zoom so ports do not keep a fake ortho Camera3D.
• godot-gdscript-mastery — Typed Vector2/Transform2D math and tooling scripts used throughout dimension-reduction helpers.

Complements

• godot-2d-animation — Sprite-sheet / AnimatedSprite2D pipeline after baking 3D models to directional frames.
• godot-shaders-basics — CanvasItem shaders for Mode-7 / perspective pitch and other screen-space depth fakes.
• godot-tilemap-mastery — TileMapLayer batching that often replaces individual 3D mesh instances in the 2D port.
• godot-navigation-pathfinding — Deeper 2D navmesh/AStarGrid2D patterns when flattening aerial/vertical routes.
• godot-audio-systems — AudioStreamPlayer3D → AudioStreamPlayer2D panning/attenuation after spatial audio is lost.
• godot-adapt-2d-to-3d — Inverse adaptation lattice when deciding which axis of the port to keep or reverse.

Downstream / consumers

• godot-performance-optimization — Escalate when the 2D port still misses frame budgets despite dimensional reduction.
• godot-platform-mobile — Common shipping target that motivates 3D→2D simplification for battery and GPU limits.
• godot-adapt-desktop-to-mobile — Broader desktop→mobile adaptation that often includes this skill’s flatten-to-2D step.

Master

• godot-master — Library router and mirrored module entry; open when discovering which Domain Skill owns a cross-cutting 2D/3D concern.