Genre: Card Game

Expert blueprint for digital card games with data-driven design and juicy UI.

NEVER Do (Expert Anti-Patterns)

Logic & Architecture

• NEVER hardcode card logic inside UI scripts; strictly encapsulate gameplay effects in Callable objects or Command resources pushed to a LIFO stack.
• NEVER perform board-state calculations (Power/Toughness) in _process(); strictly use Signal-driven triggers or a centralized EffectStack resolver.
• NEVER forget LIFO Stack Resolution; strictly use Array.push_back() and Array.pop_back() to resolve reactions from top-to-bottom.

UX & Animation

• NEVER skip Z-Index management during drag-and-drop; strictly raise the card to the front on click to prevent it sliding under other cards.
• NEVER allow instant card "teleportation" between piles; strictly use Tween animations (0.2s+) to give cards a tactile, physical feel.
• NEVER use global_position for cards in hand; strictly position them using a Curve2D (Bezier) layout with sample_baked() for smooth, non-circular arcs.
• NEVER allow instant card "teleportation" between piles; strictly use create_tween() and tween_property chainings (0.2s+) for juicy card-feel.

Deck & State Management

• NEVER forget to handle Empty Deck scenarios; strictly implement auto-reshuffle of the discard pile to prevent soft-locks.
• NEVER use floating point numbers for discrete card stats; strictly use int for Costs, Attack, and Health to avoid precision drift.
• NEVER use standard Control nodes for mass tokens/battlefields; strictly use _draw() custom drawing to bypass SceneTree overhead when rendering 100+ cards or map icons.
• NEVER rely on SceneTree order for hand logic; strictly manage logical order in an Array and update visuals via queue_redraw().
• NEVER erase array elements during a standard for loop; strictly iterate in reverse or use filter() to avoid indexing errors.
• NEVER forget to provide parameterless constructors in _init(); otherwise, Resources will fail to load in the Inspector.

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🛠 Expert Components (scripts/)

Original Expert Patterns

• card_effect_resolution.gd - Stack-based effect resolver (LIFO/FIFO) handling nested triggers and counter-play.

Modular Components

• card_data_resource.gd - Data-driven card definitions allowing Inspector-based design.
• deck_shuffle_bag.gd - Secure randomization patterns for uniform card distribution.
• turn_state_machine.gd - Managing rigid phases (Draw, Play, Combat) via state matching.
• card_drag_drop.gd - Implementation of native _get_drag_data() for Control nodes.
• board_query_filter.gd - Functional filter() patterns for querying board metadata.
• card_tween_manager.gd - Managing interruptible card juice and board transitions.
• reactive_card_ui.gd - Resource-signal driven UI for automatic visual state updates.
• board_state_dictionary.gd - Grid-based tracking (Vector2i) decoupled from Node order.
• match_state_resetter.gd - Clean-up pattern for in-match temporary Resource modifications.
• deck_builder_validator.gd - Backend logic for deck-building constraints and mana curves.

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Core Loop

1. Draw: Player draws cards from a deck into their hand.
2. Evaluate: Player assesses board state, mana/energy, and card options.
3. Play: Player plays cards to trigger effects (damage, buff, summon).
4. Resolve: Effects occur immediately or go onto a stack.
5. Discard/End: Unused cards are discarded (roguelike) or kept (TCG), turn ends.

Skill Chain

Phase	Skills	Purpose
1. Data	resources, custom-resources	Defining Card properties (Cost, Type, Effect)
2. UI	control-nodes, layout-containers	Hand layout, card positioning, tooltips
3. Input	drag-and-drop, state-machines	Dragging cards to targets, hovering
4. Logic	command-pattern, signals	Executing card effects, turn phases
5. Polish	godot-tweening, shaders	Draw animations, holographic foils

Architecture Overview

1. Card Data (Resource-based)

Godot Resources are perfect for card data.

# card_data.gd
extends Resource
class_name CardData

enum Type { ATTACK, SKILL, POWER }
enum Target { ENEMY, SELF, ALL_ENEMIES }

@export var id: String
@export var name: String
@export_multiline var description: String
@export var cost: int
@export var type: Type
@export var target_type: Target
@export var icon: Texture2D
@export var effect_script: Script # Custom logic per card

2. Deck Manager

Handles the piles: Draw Pile, Hand, Discard Pile, Exhaust Pile.

# deck_manager.gd
var draw_pile: Array[CardData] = []
var hand: Array[CardData] = []
var discard_pile: Array[CardData] = []

func draw_cards(amount: int) -> void:
    for i in amount:
        if draw_pile.is_empty():
            reshuffle_discard()
            
        if draw_pile.is_empty(): 
            break # No cards left
            
        var card = draw_pile.pop_back()
        hand.append(card)
        card_drawn.emit(card)

func reshuffle_discard() -> void:
    draw_pile.append_array(discard_pile)
    discard_pile.clear()
    draw_pile.shuffle()

3. Card Visual (UI)

The interactive node representing a card in hand.

# card_ui.gd
extends Control

var card_data: CardData
var start_pos: Vector2
var is_dragging: bool = false

func _gui_input(event: InputEvent) -> void:
    if event is InputEventMouseButton and event.button_index == MOUSE_BUTTON_LEFT:
        if event.pressed:
            start_drag()
        else:
            end_drag()

func _process(delta: float) -> void:
    if is_dragging:
        global_position = get_global_mouse_position() - size / 2
    else:
        # Hover effect or return to hand position
        pass

Key Mechanics Implementation

Effect Resolution (Command Pattern)

Decouple the "playing" of a card from its "effect".

func play_card(card: CardData, target: Node) -> void:
    if current_energy < card.cost:
        show_error("Not enough energy")
        return
        
    current_energy -= card.cost
    
    # Execute effect
    var effect = card.effect_script.new()
    effect.execute(target)
    
    move_to_discard(card)

Hand Layout (Arching)

Cards in hand usually form an arc. Use a math formula (Bezier or Circle) to position them based on index and total_cards.

func update_hand_visuals() -> void:
    var center_x = screen_width / 2
    var radius = 1000.0
    var angle_step = 5.0
    
    for i in hand_visuals.size():
        var card = hand_visuals[i]
        var angle = deg_to_rad((i - hand_visuals.size() / 2.0) * angle_step)
        var target_pos = Vector2(
            center_x + sin(angle) * radius,
            screen_height + cos(angle) * radius
        )
        card.target_rotation = angle
        card.target_position = target_pos

Common Pitfalls

1. Complexity Overload: Too many keywords. Fix: Stick to 3-5 core keywords (e.g., Taunt, Poison, Shield) and expand slowly.
2. Unreadable Text: Tiny fonts on cards. Fix: Use icons for common stats (Damage, Block) and keep text short.
3. Animation Lock: Waiting for slow animations to finish before playing the next card. Fix: Allow queueing actions or keep animations snappy (< 0.3s).

Godot-Specific Tips

• MouseFilter: Getting drag/drop to work with overlapping UI requires careful setup of mouse_filter (Pass vs Stop).
• Z-Index: Use z_index or CanvasLayer to ensure the dragged card is always on top of everything else.
• Tweens: Essential! Tween position, rotation, and scale for that "juicy" Hearthstone/Slay the Spire feel.

Reference

• Master Skill: godot-master