store belts as buildings and fix issue that belts could not be selected

src/lib/sim/BuildingSystem.cpp

@@ -241,24 +241,6 @@ EntityId BuildingSystem::place(BuildingType type, QPoint anchor,
 
 int BuildingSystem::demolish(EntityId id)
 {
-    // Belt / splitter?
-    const std::map<EntityId, BeltEntry>::iterator beltIt = m_beltEntities.find(id);
-    if (beltIt != m_beltEntities.end())
-    {
-        const QPoint tile = beltIt->second.tile;
-        const BuildingType btype = beltIt->second.type;
-        m_belts.removeTile(tile);
-        m_tileOccupancy.erase({tile.x(), tile.y()});
-        m_beltEntities.erase(beltIt);
-
-        const BuildingDef* def = findBuildingDef(btype);
-        if (def)
-        {
-            return def->cost * m_config.world.refundPercentage / 100;
-        }
-        return 0;
-    }
-
     // Construction queue?
     for (std::deque<ConstructionSite>::iterator it = m_constructionQueue.begin();
          it != m_constructionQueue.end();
@@ -287,6 +269,10 @@ int BuildingSystem::demolish(EntityId id)
     {
         if (it->id == id)
         {
+            if (it->type == BuildingType::Belt || it->type == BuildingType::Splitter)
+            {
+                m_belts.removeTile(it->anchor);
+            }
             const BuildingDef* def = findBuildingDef(it->type);
             for (const QPoint& cell : it->bodyCells)
             {
@@ -381,25 +367,7 @@ void BuildingSystem::tickConstruction(Tick currentTick)
         return;
     }
 
-    // Promote construction site — belts/splitters go into BeltSystem, others become Buildings.
+    // Promote construction site to an operational Building.
-    if (front.type == BuildingType::Belt)
-    {
-        m_belts.placeBelt(front.anchor, front.rotation);
-        m_beltEntities[front.id] = BeltEntry{front.anchor, BuildingType::Belt, front.rotation, front.rotation};
-    }
-    else if (front.type == BuildingType::Splitter)
-    {
-        const BuildingDef* def = findBuildingDef(front.type);
-        assert(def != nullptr);
-        const ParsedSurfaceMask mask = parseSurfaceMask(def->surfaceMask, front.rotation);
-        assert(mask.outputPorts.size() >= 2);
-        const Rotation outA = mask.outputPorts[0].direction;
-        const Rotation outB = mask.outputPorts[1].direction;
-        m_belts.placeSplitter(front.anchor, outA, outB);
-        m_beltEntities[front.id] = BeltEntry{front.anchor, BuildingType::Splitter, outA, outB};
-    }
-    else
-    {
     const BuildingDef* def = findBuildingDef(front.type);
     const ParsedSurfaceMask mask = parseSurfaceMask(
         def ? def->surfaceMask : std::vector<std::string>{},
@@ -444,8 +412,20 @@ void BuildingSystem::tickConstruction(Tick currentTick)
         }
     }
 
-        m_buildings.push_back(std::move(building));
+    // Register with BeltSystem before the move (mask stays valid).
+    if (front.type == BuildingType::Belt)
+    {
+        m_belts.placeBelt(front.anchor, front.rotation);
     }
+    else if (front.type == BuildingType::Splitter)
+    {
+        assert(mask.outputPorts.size() >= 2);
+        m_belts.placeSplitter(front.anchor,
+                              mask.outputPorts[0].direction,
+                              mask.outputPorts[1].direction);
+    }
+
+    m_buildings.push_back(std::move(building));
 
     m_constructionQueue.pop_front();
 
@@ -774,15 +754,30 @@ std::vector<ConstructionSite> BuildingSystem::allSites() const
 std::vector<BuildingSystem::BeltTileInfo> BuildingSystem::allBeltTiles() const
 {
     std::vector<BeltTileInfo> result;
-    result.reserve(m_beltEntities.size());
+    for (const Building& b : m_buildings)
-    for (const std::map<EntityId, BeltEntry>::value_type& kv : m_beltEntities)
     {
+        if (b.type != BuildingType::Belt && b.type != BuildingType::Splitter)
+        {
+            continue;
+        }
         BeltTileInfo info;
-        info.id         = kv.first;
+        info.id   = b.id;
-        info.tile       = kv.second.tile;
+        info.tile = b.bodyCells.empty() ? b.anchor : b.bodyCells[0];
-        info.type       = kv.second.type;
+        info.type = b.type;
-        info.directionA = kv.second.directionA;
+        if (!b.outputPorts.empty())
-        info.directionB = kv.second.directionB;
+        {
+            info.directionA = b.outputPorts[0].direction;
+            info.directionB = b.outputPorts[0].direction;
+        }
+        else
+        {
+            info.directionA = b.rotation;
+            info.directionB = b.rotation;
+        }
+        if (b.type == BuildingType::Splitter && b.outputPorts.size() >= 2)
+        {
+            info.directionB = b.outputPorts[1].direction;
+        }
         result.push_back(info);
     }
     return result;
@@ -907,6 +902,10 @@ bool BuildingSystem::removeBuilding(EntityId id)
     {
         if (it->id == id)
         {
+            if (it->type == BuildingType::Belt || it->type == BuildingType::Splitter)
+            {
+                m_belts.removeTile(it->anchor);
+            }
             for (const QPoint& cell : it->bodyCells)
             {
                 m_tileOccupancy.erase({cell.x(), cell.y()});

src/lib/sim/BuildingSystem.h

@@ -23,8 +23,8 @@
 
 // Manages building placement, construction queuing, and the per-tick
 // production loop (belt→building pull, production, building→belt push).
-// Belt and Splitter types are forwarded to BeltSystem rather than stored
+// All types including Belt and Splitter are stored as Building instances;
-// as Building instances.
+// BeltSystem owns the per-tile simulation data (item slots, flow).
 class BuildingSystem
 {
 public:
@@ -106,14 +106,6 @@ public:
     void forEachBuilding(std::function<void(Building&)> fn);
 
 private:
-    struct BeltEntry
-    {
-        QPoint       tile;
-        BuildingType type;       // Belt or Splitter
-        Rotation     directionA; // Belt: its direction; Splitter: first output
-        Rotation     directionB; // Splitter: second output; Belt: same as directionA
-    };
-
     const BuildingDef*  findBuildingDef(BuildingType type) const;
     const RecipeDef*    findRecipe(const std::string& id, BuildingType type) const;
     const ShipDef*      findShipDef(const std::string& id) const;
@@ -131,7 +123,6 @@ private:
 
     std::vector<Building>           m_buildings;
     std::deque<ConstructionSite>    m_constructionQueue;
-    std::map<EntityId, BeltEntry>   m_beltEntities;
 
     // Maps every occupied body-cell coordinate to the entity that owns it.
     std::map<std::pair<int, int>, EntityId> m_tileOccupancy;

src/test/BuildingTest.cpp

@@ -116,7 +116,9 @@ TEST_CASE("BuildingSystem: placing a belt registers it with BeltSystem after con
     runTicks(bs, belts, static_cast<int>(secondsToTicks(1.0)) + 1, tick);
 
     REQUIRE(belts.tryPutItem(QPoint(5, 5), makeItem("iron_ore")));
-    REQUIRE(bs.allBuildings().empty());  // belts do not create Building instances
+    REQUIRE(bs.allBuildings().size() == 1);
+    REQUIRE(bs.allBuildings()[0].type == BuildingType::Belt);
+    REQUIRE(bs.allBuildings()[0].anchor == QPoint(5, 5));
 }
 
 TEST_CASE("BuildingSystem: placed building enters construction queue", "[building]")

src/ui/GameWorldView.cpp

@@ -396,10 +396,6 @@ EntityId GameWorldView::buildingAtTile(QPoint tile) const
             if (cell == tile) { return b.id; }
         }
     }
-    for (const BuildingSystem::BeltTileInfo& info : m_sim->buildings().allBeltTiles())
-    {
-        if (info.tile == tile) { return info.id; }
-    }
     return kInvalidEntityId;
 }
 
@@ -542,10 +538,23 @@ void GameWorldView::drawBuildings(QPainter& painter)
             painter.fillRect(tileRect(cell), bv.fill);
         }
 
+        // Belts and splitters are 1×1 on their body cell; other buildings use
+        // the full footprint bounding box for their outline and glyph.
+        QRectF bboxRect;
+        const bool isBeltLike = (b.type == BuildingType::Belt
+                                 || b.type == BuildingType::Splitter);
+        if (isBeltLike && !b.bodyCells.empty())
+        {
+            const QPointF tl = tileToWidget(b.bodyCells[0]);
+            bboxRect = QRectF(tl.x(), tl.y(), tilePx(), tilePx());
+        }
+        else
+        {
             const QPointF tl = tileToWidget(b.anchor);
-        const QRectF  bboxRect(tl.x(), tl.y(),
+            bboxRect = QRectF(tl.x(), tl.y(),
                 b.footprint.width()  * static_cast<qreal>(tilePx()),
                 b.footprint.height() * static_cast<qreal>(tilePx()));
+        }
 
         painter.setPen(QPen(bv.outline, 1));
         painter.setBrush(Qt::NoBrush);
@@ -576,27 +585,6 @@ void GameWorldView::drawBuildings(QPainter& painter)
         }
     }
 
-    // Belt and splitter tiles (stored separately from regular buildings)
-    for (const BuildingSystem::BeltTileInfo& info : m_sim->buildings().allBeltTiles())
-    {
-        const std::map<BuildingType, BuildingVisuals>::const_iterator it =
-            m_visuals->buildings.find(info.type);
-        if (it == m_visuals->buildings.end()) { continue; }
-        const BuildingVisuals& bv = it->second;
-
-        painter.setPen(Qt::NoPen);
-        painter.fillRect(tileRect(info.tile), bv.fill);
-        painter.setPen(QPen(bv.outline, 1));
-        painter.setBrush(Qt::NoBrush);
-        painter.drawRect(tileRect(info.tile));
-
-        drawPortGlyph(painter, info.tile, info.directionA, bv.outline);
-        if (info.type == BuildingType::Splitter)
-        {
-            drawPortGlyph(painter, info.tile, info.directionB, bv.outline);
-        }
-    }
-
     painter.setOpacity(0.5);
     for (const ConstructionSite& s : m_sim->buildings().allSites())
     {
@@ -782,17 +770,6 @@ void GameWorldView::drawOverlays(QPainter& painter)
                 painter.fillRect(tileRect(cell), m_visuals->overlays.demolishTint);
             }
         }
-        else
-        {
-            for (const BuildingSystem::BeltTileInfo& info : m_sim->buildings().allBeltTiles())
-            {
-                if (info.id == m_demolishHoverId)
-                {
-                    painter.fillRect(tileRect(info.tile), m_visuals->overlays.demolishTint);
-                    break;
-                }
-            }
-        }
     }
 
     // Box-select rectangle