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Grid Placement v6.0

Refund on Demolish

How object demolish refunds work through BuildCost, RefundService, and RefundCalculator.

Status
Current
Version
v6.0
Source updated
Active v6.0 guide line from Grid Placement repo
Generated on
2026-09-01

Grid Placement can refund some or all of an object's build cost when that object is demolished. The plugin does not own your inventory; your game supplies a small id-based inventory bridge.

This feature applies to placed objects. Terrain painting is cell data, so terrain economy/refunds remain game-owned.

Data flow

SpendMaterialsRuleById defines cost
→ BuildCost resolves that cost for the placed object
→ demolish reaches the pre-demolish/refund path
→ RefundCalculator applies refund_ratio
→ RefundService sends id + amount to your inventory bridge

Use one cost source for both spending and refunds so those values cannot drift.

Main types

Type Purpose
SpendMaterialsRuleById Defines id-keyed object build costs.
BuildCost Resolved cost for a placed/manipulatable object.
RefundCalculator Calculates refunded id→amount values.
RefundService Applies refunds through the configured inventory bridge.
Refunder Optional pre-demolish hook that can inspect/veto demolition.

The current public service name is RefundService; old RefundSystem wording is legacy.

Inventory bridge

The same id contract can serve spending and refunding:

func get_count_by_id(id:StringName)-> int:
    return GameInventory.get_item_count(id)

func try_remove_by_id(id:StringName, amount:int)-> int:
    return GameInventory.remove_items(id, amount)

func try_add_by_id(id:StringName, amount:int)-> int:
    return GameInventory.add_items(id, amount)

Return the amount actually added/removed. That lets capacity-limited inventories report a partial refund correctly.

Configure refunds

RefundService owns the normal integration. Configure its refund ratio/rounding and make the inventory bridge reachable through the placement owner/bootstrap configuration.

Example policy:

build cost: 100 wood
refund_ratio: 0.5
refund: 50 wood

Configure one refund service for a placement setup. Do not attach an independent refund service to every building; multiple handlers can refund the same demolition more than once.

Use RefundCalculator directly only when your game intentionally owns a custom demolish pipeline. Use a custom Refunder when demolition itself needs a veto/inspection step.

Common mistakes

  • Spend and refund ids differ (&"Wood" vs &"wood").
  • Several handlers refund the same object.
  • The inventory bridge cannot be resolved from the active placement owner/configuration.
  • A custom runtime discount changes the paid cost but the placed object's resolved BuildCost is not updated.
  • Terrain painting is treated as if it were an object demolition workflow.