Drop Areas (DropAreaBase)

La clase base DropAreaBase te permite crear drop areas personalizadas sin conocer los internals del sistema. Se encarga de toda la mecánica de interacción, mientras que la subclase define únicamente qué hacer con los items.

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Dos patrones de uso

flowchart TD
    BASE["DropAreaBase"]
    BASE --> SIMPLE["Simple Consumption"]
    BASE --> DELEG["Delegation"]

    SIMPLE --> WDZ["WorldDropZone\nTrashZone\nSellZone"]
    DELEG --> IDA["InventoryDropArea"]

    style BASE fill:#7c4dff,color:#fff
    style SIMPLE fill:#00c853,color:#fff
    style DELEG fill:#ff6d00,color:#fff

Patrón	Idea	Cuándo usarlo
Simple Consumption	Sobrescribe CanAcceptEntry + ProcessEntry. La eliminación del source es automática	Zona del mundo, papelera, venta: cualquier target sin inventario
Delegation	Sobrescribe GetDropProcessor(), devuelve tu propio IDropProcessor	Áreas de inventario con lógica compleja (policy, swap, conversión)

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Simple Consumption

Una subclase mínima solo necesita dos métodos:

public class TrashDropZone : DropAreaBase
{
    protected override bool CanAcceptEntry(DragEntry entry)
    {
        // Accept everything
        return entry.Stack != null && !entry.Stack.IsEmpty;
    }

    protected override bool ProcessEntry(ItemStack freshStack, DragEntry entry)
    {
        // Do nothing --- items simply disappear.
        // Source removal is handled automatically by the base class.
        return true;
    }
}

Cómo funciona internamente

flowchart TD
    A["Player drops item"] --> B["DropAreaBase starts processing"]
    B --> C["For each entry"]
    C --> D{"CanAcceptEntry(entry)?"}
    D -->|Yes| E["Copy stack from source slot"]
    E --> F{"ProcessEntry(freshStack, entry)"}
    F -->|true| G["Remove items from source + emit events"]
    G --> H{"More entries left?"}
    H -->|Yes| C
    H -->|No| I["DropResult.Succeeded"]

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Delegation

Cuando necesitas lógica compleja de drop (el pipeline de transferencia, policies, swaps), sobrescribe GetDropProcessor():

public class CustomInventoryArea : DropAreaBase
{
    [SerializeField] private UniversalInventory _inventory;

    protected override bool TryActivateAsFocusedTarget()
    {
        if (_inventory == null) return false;
        // Custom validation...
        DragManager.PushDropTarget(this);
        return true;
    }

    public override IDropProcessor GetDropProcessor()
    {
        // Return your own processor instead of this
        return new InventoryDropProcessor(_inventory, DragManager?.GlobalRules);
    }

    public override BaseSlot GetTargetSlot() => null;
}

En este caso, CanAcceptEntry y ProcessEntry de la clase base nunca se llaman: todo el procesamiento pasa a través del processor devuelto.

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Qué maneja la clase base

DropAreaBase hereda de Selectable e implementa IDropTarget + IDropProcessor.

Mecánicas automáticas

Mecánica	Descripción
Seguimiento del puntero	OnPointerEnter/Exit hace push/pop automático en la target stack de DragAndDropManager
Eventos de estado	Se suscribe a OnDragStarted/Cancelled/Completed/Ended para gestionar interactable y raycast
Gestión de raycast	raycastTarget solo está activado durante un drag
Soporte para gamepad	La herencia de Selectable aporta navegación y focus de serie
Lifecycle de highlight	OnBecomeActiveTarget/OnBecomeInactiveTarget llaman a OnHighlightChanged
Eliminación del source	En el patrón simple consumption, eliminación automática del source slot con emisión de eventos

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Todos los puntos de override

public abstract class DropAreaBase : Selectable, IDropTarget, IDropProcessor
{
    // ── Simple Consumption ──────────────────────
    // Override for non-inventory zones

    protected virtual bool CanAcceptEntry(DragEntry entry);
    // Can this zone accept the entry?
    // Default: true

    protected virtual bool ProcessEntry(ItemStack freshStack, DragEntry entry);
    // What to do with the items? Source removal is automatic.
    // Default: false (no-op)

    // ── Delegation ──────────────────────────────
    // Override for inventory-based zones

    public virtual IDropProcessor GetDropProcessor();
    // Default: this (simple consumption)

    public virtual BaseSlot GetTargetSlot();
    // Default: null

    // ── Common ──────────────────────────────────

    internal virtual bool TryActivateAsFocusedTarget();
    // Called when cursor enters during a drag.
    // Default: checks CanAcceptEntry on first entry + PushDropTarget.

    protected virtual void OnTargetDeactivated();
    // Called when cursor leaves. For resetting internal state.

    protected virtual void OnHighlightChanged(bool highlighted, bool canAccept);
    // Called when highlight state changes. highlighted = is the zone active,
    // canAccept = can it accept the current item.

    protected virtual bool RemoveFromSource { get; }
    // Whether to remove items from source after ProcessEntry.
    // Default: true. Override to false for copy/preview zones.
}

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Ejemplos de subclase

WorldDropZone --- Spawn en mundo 3D

El fragmento siguiente sigue la implementación actual de Demo2 Loot.

public class WorldDropZone : DropAreaBase
{
    [SerializeField] private Transform _spawnPoint;

    protected override bool CanAcceptEntry(DragEntry entry)
    {
        // All adapters must have a 3D prefab
        foreach (var adapter in entry.Stack.Adapters)
            if (adapter is not ItemAdapterSoWith3DAdapter with3D || with3D.WorldPrefab == null)
                return false;
        return true;
    }

    protected override bool ProcessEntry(ItemStack freshStack, DragEntry entry)
    {
        foreach (var adapter in freshStack.Adapters)
        {
            var with3D = (ItemAdapterSoWith3DAdapter)adapter;
            Instantiate(with3D.WorldPrefab, _spawnPoint.position, Quaternion.identity);
        }
        return true;
    }
}

SellDropZone --- Vender por oro

public class SellDropZone : DropAreaBase
{
    [SerializeField] private PlayerWallet _wallet;

    protected override bool CanAcceptEntry(DragEntry entry)
    {
        return entry.Stack.PrimaryAdapter is ISellable;
    }

    protected override bool ProcessEntry(ItemStack freshStack, DragEntry entry)
    {
        int total = 0;
        foreach (var adapter in freshStack.Adapters)
            total += ((ISellable)adapter).SellPrice;
        _wallet.AddGold(total);
        return true;
    }
}

PreviewDropZone --- Ver sin eliminar

public class PreviewDropZone : DropAreaBase
{
    protected override bool RemoveFromSource => false;

    protected override bool CanAcceptEntry(DragEntry entry)
        => entry.Stack?.PrimaryAdapter is IPreviewable;

    protected override bool ProcessEntry(ItemStack freshStack, DragEntry entry)
    {
        ShowPreview(freshStack);
        return true;
    }
}

RemoveFromSource = false desactiva la eliminación automática del source. Los items permanecen en el inventario original.

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Highlighting

Sobrescribe OnHighlightChanged para añadir feedback visual:

[SerializeField] private Image _highlight;
[SerializeField] private Color _validColor = Color.green;
[SerializeField] private Color _invalidColor = Color.red;

protected override void OnHighlightChanged(bool highlighted, bool canAccept)
{
    if (_highlight == null) return;
    _highlight.color = highlighted
        ? (canAccept ? _validColor : _invalidColor)
        : Color.clear;
}

canAccept se determina automáticamente mediante CanAcceptEntry sobre la primera entry durante el hover.

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Referencia

Clase	Patrón	Descripción
DropAreaBase	---	Clase base para todas las drop areas
WorldDropZone	Simple Consumption	Crea objetos 3D en el mundo
InventoryDropArea	Delegation	Drop dentro del inventario vía el pipeline de transferencia