Throw item if placement preview is invalid

scripts/PickupController.gd

@@ -18,7 +18,7 @@ func _ready() -> void:
 
 func _input(event: InputEvent) -> void:
 	if Input.mouse_mode != Input.MOUSE_MODE_CAPTURED: return
-	
+
 	ensure_current_item_valid()
 	if !current_item: return
 
@@ -49,13 +49,23 @@ func _input(event: InputEvent) -> void:
 			is_current_item_held = false
 
 			# Parent item back to the world.
+			var prev_transform := current_item.global_transform
+			current_item.freeze = false
+			# FIXME: Item appears to just float after unfreezing.
+
 			remove_child(current_item)
 			world.add_child(current_item)
 
-			# Set item's transform to where the placement preview is.
-			# TODO: If placement preview is not valid, don't allow placing the item.
-			current_item.global_transform = placement_preview.global_transform
-			current_item.freeze = false
+			# If placement is valid, move item to the preview's location.
+			# Otherwise just restore the transform of where it was held.
+			if placement_preview.visible:
+				current_item.global_transform = placement_preview.global_transform
+			else:
+				current_item.global_transform = prev_transform
+				# Throw item forward and up a bit.
+				var cam_basis := camera.global_transform.basis
+				var direction := -cam_basis.z + cam_basis.y
+				current_item.apply_impulse(direction * 2)
 
 			placement_preview.queue_free()
 			placement_preview = null
@@ -89,6 +99,10 @@ func _physics_process(_delta: float) -> void:
 			pos += half_size * (normal * placement_preview.global_transform.basis)
 			pos  = pos.snapped(Item.GRID_SIZE * Vector3.ONE)
 			placement_preview.global_position = pos
+			placement_preview.visible = true
+
+		else:
+			placement_preview.visible = false
 
 	else:
 		# Remove the outline from the previously looked-at item.