Animate items entering building input ports

src/lib/sim/BuildingSystem.h

@@ -132,6 +132,12 @@ public:
     void forEachEmergingItem(
         const std::function<void(const ItemType&, QPointF)>& visit) const;
 
+    // Visits every item currently travelling inward on a building input port's
+    // virtual input belt (REQ-MAT-INPUT-INTAKE), passing the item type and its
+    // world-space centre (in tile units). Least-progressed first (drawn bottom).
+    void forEachIncomingItem(
+        const std::function<void(const ItemType&, QPointF)>& visit) const;
+
     // Returns the entity id of the building or construction site whose footprint
     // exactly coincides with the ghost (type, anchor, rot) and is of the same
     // building type.  Returns nullopt otherwise.