Animate items emerging from building output ports

src/lib/sim/BuildingSystem.h

@@ -10,6 +10,7 @@
 #include <vector>
 
 #include <QPoint>
+#include <QPointF>
 #include <QVector2D>
 
 #include "BeltSystem.h"
@@ -94,7 +95,10 @@ public:
     void tickBeltPull();
     void tickProduction(Tick currentTick);
     void tickShipyardProduction(Tick currentTick);
-    void tickBeltPush();
+    // Advances each building's virtual output belts, hands finished items off onto
+    // the adjacent real belt, and feeds new buffered items into them
+    // (REQ-MAT-OUTPUT-EMERGE).
+    void tickOutputBelts();
 
     // -- Queries -------------------------------------------------------------
     struct BeltTileInfo
@@ -121,6 +125,13 @@ public:
     std::vector<BeltTileInfo> allBeltTiles()             const;
     bool                      isTileOccupied(QPoint tile) const;
 
+    // Visits every item currently emerging from a building output port on its
+    // virtual output belt (REQ-MAT-OUTPUT-EMERGE), passing the item type and its
+    // world-space centre (in tile units). Least-progressed first (drawn bottom) so
+    // callers can paint in visit order (REQ-GW-TILE-SIZE ordering).
+    void forEachEmergingItem(
+        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.