Animate items entering building input ports

src/lib/sim/Building.h

@@ -96,6 +96,31 @@ struct Building
         return count;
     }
 
+    // Items currently travelling inward on each input port's virtual input belt
+    // (REQ-MAT-INPUT-INTAKE); one lane per input port, parallel to inputPorts. Each
+    // lane holds slots at progress [0.0, 0.5], front (highest progress) first. An
+    // in-transit item has reserved a slot in its per-material input buffer but is
+    // not yet consumable — it enters the buffer only on reaching progress 0.5.
+    std::vector<std::vector<BeltItemSlot>> incomingItems;
+
+    // Buffered plus in-transit count of one input material. The acceptance/space
+    // test (REQ-MAT-INPUT-PORTS, REQ-MAT-INPUT-INTAKE) counts in-transit items, so
+    // buffered + reserved never exceeds the material's cap (REQ-MAT-INPUT-BUFFER).
+    int pendingInputCount(const ItemType& type) const
+    {
+        int count = 0;
+        const std::map<ItemType, int>::const_iterator it = inputBuffer.counts.find(type);
+        if (it != inputBuffer.counts.end()) { count = it->second; }
+        for (const std::vector<BeltItemSlot>& lane : incomingItems)
+        {
+            for (const BeltItemSlot& slot : lane)
+            {
+                if (slot.item.type == type) { ++count; }
+            }
+        }
+        return count;
+    }
+
     // Pre-computed from surface mask at placement; in absolute world coordinates.
     std::vector<QPoint> bodyCells;
     std::vector<Port>   outputPorts;