extract SelectionController

src/lib/core/CMakeLists.txt

@@ -16,6 +16,7 @@ SET(HDRS
     ${CMAKE_CURRENT_SOURCE_DIR}/TunnelCompletion.h
     ${CMAKE_CURRENT_SOURCE_DIR}/WorldCoordinates.h
     ${CMAKE_CURRENT_SOURCE_DIR}/WorldCamera.h
+    ${CMAKE_CURRENT_SOURCE_DIR}/SelectionController.h
     PARENT_SCOPE
 )
 
@@ -29,6 +30,7 @@ SET(SRCS
     ${CMAKE_CURRENT_SOURCE_DIR}/TunnelCompletion.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/WorldCoordinates.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/WorldCamera.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/SelectionController.cpp
     PARENT_SCOPE
 )
 

src/lib/core/SelectionController.cpp

@@ -0,0 +1,165 @@
+#include "SelectionController.h"
+
+#include <algorithm>
+#include <memory>
+
+#include "DebrisSelectionChangedEvent.h"
+#include "EntitySelectionChangedEvent.h"
+#include "EventManager.h"
+#include "SelectionChangedEvent.h"
+
+namespace
+{
+
+template <typename T>
+bool contains(const std::vector<T>& items, const T& item)
+{
+    return std::find(items.begin(), items.end(), item) != items.end();
+}
+
+// Applies `hits` to `selection` per `mode`. Replace is handled by the caller so
+// that an empty hit list can mean "clear this category" there but "leave this
+// category alone" here.
+template <typename T>
+void combine(std::vector<T>& selection, const std::vector<T>& hits, SelectionMode mode)
+{
+    for (const T& hit : hits)
+    {
+        const typename std::vector<T>::iterator it =
+            std::find(selection.begin(), selection.end(), hit);
+        if (it == selection.end())
+        {
+            selection.push_back(hit);
+        }
+        else if (mode == SelectionMode::Toggle)
+        {
+            // Only a toggle removes; an additive box drag never deselects.
+            selection.erase(it);
+        }
+    }
+}
+
+}  // namespace
+
+const std::vector<BuildingId>& SelectionController::getSelectedBuildings() const
+{
+    return m_buildings;
+}
+
+const std::vector<entt::entity>& SelectionController::getSelectedActors() const
+{
+    return m_actors;
+}
+
+const std::vector<entt::entity>& SelectionController::getSelectedDebris() const
+{
+    return m_debris;
+}
+
+bool SelectionController::isActorSelected(entt::entity actor) const
+{
+    return contains(m_actors, actor);
+}
+
+bool SelectionController::isDebrisSelected(entt::entity debris) const
+{
+    return contains(m_debris, debris);
+}
+
+void SelectionController::selectBuildings(const std::vector<BuildingId>& ids,
+                                          SelectionMode mode)
+{
+    // Buildings win over field objects (REQ-UI-SELECTION-CATEGORIES).
+    if (clearActorsQuietly()) { publishActors(); }
+    if (clearDebrisQuietly()) { publishDebris(); }
+
+    if (mode == SelectionMode::Replace)
+    {
+        m_buildings = ids;
+    }
+    else
+    {
+        combine(m_buildings, ids, mode);
+    }
+    publishBuildings();
+}
+
+void SelectionController::selectFieldObjects(const std::vector<entt::entity>& actors,
+                                             const std::vector<entt::entity>& debris,
+                                             SelectionMode mode)
+{
+    if (clearBuildingsQuietly()) { publishBuildings(); }
+
+    if (mode == SelectionMode::Replace)
+    {
+        m_actors = actors;
+        m_debris = debris;
+    }
+    else
+    {
+        combine(m_actors, actors, mode);
+        combine(m_debris, debris, mode);
+    }
+    publishActors();
+    publishDebris();
+}
+
+void SelectionController::clearAll()
+{
+    if (clearBuildingsQuietly()) { publishBuildings(); }
+    if (clearActorsQuietly())    { publishActors(); }
+    if (clearDebrisQuietly())    { publishDebris(); }
+}
+
+void SelectionController::setSelectedActors(std::vector<entt::entity> actors)
+{
+    if (actors == m_actors) { return; }
+    m_actors = std::move(actors);
+    publishActors();
+}
+
+void SelectionController::setSelectedDebris(std::vector<entt::entity> debris)
+{
+    if (debris == m_debris) { return; }
+    m_debris = std::move(debris);
+    publishDebris();
+}
+
+bool SelectionController::clearBuildingsQuietly()
+{
+    if (m_buildings.empty()) { return false; }
+    m_buildings.clear();
+    return true;
+}
+
+bool SelectionController::clearActorsQuietly()
+{
+    if (m_actors.empty()) { return false; }
+    m_actors.clear();
+    return true;
+}
+
+bool SelectionController::clearDebrisQuietly()
+{
+    if (m_debris.empty()) { return false; }
+    m_debris.clear();
+    return true;
+}
+
+void SelectionController::publishBuildings() const
+{
+    EventManager::getInstance()->sendEventImmediately(
+        std::make_shared<SelectionChangedEvent>(m_buildings));
+}
+
+void SelectionController::publishActors() const
+{
+    EventManager::getInstance()->sendEventImmediately(
+        std::make_shared<EntitySelectionChangedEvent>(m_actors));
+}
+
+void SelectionController::publishDebris() const
+{
+    EventManager::getInstance()->sendEventImmediately(
+        std::make_shared<DebrisSelectionChangedEvent>(m_debris));
+}

src/lib/core/SelectionController.h

@@ -0,0 +1,75 @@
+#pragma once
+
+#include <vector>
+
+#include "BuildingId.h"
+#include "entt/entity/entity.hpp"
+
+// How a new hit combines with what is already selected.
+enum class SelectionMode
+{
+    Replace,  // plain click or drag: the hit becomes the whole selection
+    Toggle,   // Ctrl + click: the hit joins the selection, or leaves it if present
+    Add       // Ctrl + box drag: the hits join the selection, never leave it
+};
+
+// The player's current selection across the three categories, and the rules that
+// govern moving between them (REQ-UI-SELECTION-CATEGORIES).
+//
+// The rules were previously written out once for point-clicks and once for box
+// drags, which is why they live here now: buildings win over field objects, so
+// selecting a building clears actors and debris, and selecting either of those
+// clears buildings — but actors and debris coexist with each other
+// (REQ-UI-ENTITY-CLICK-SELECT, REQ-UI-DEBRIS-CLICK-SELECT, REQ-UI-MULTI-SELECT,
+// REQ-UI-DEBRIS-MULTI-SELECT). A point-click and a box drag then differ only in
+// the SelectionMode they pass and in how many hits they pass.
+//
+// Every mutator publishes the change events, so callers never emit them by hand.
+// Hit-testing is not done here: callers resolve what was hit and pass the result
+// in, which keeps this free of any simulation dependency.
+class SelectionController
+{
+public:
+    const std::vector<BuildingId>&   getSelectedBuildings() const;
+    const std::vector<entt::entity>& getSelectedActors() const;
+    const std::vector<entt::entity>& getSelectedDebris() const;
+
+    bool isActorSelected(entt::entity actor) const;
+    bool isDebrisSelected(entt::entity debris) const;
+
+    // Selects buildings and/or construction sites, clearing any field selection.
+    // Always publishes SelectionChangedEvent, even when the result is unchanged,
+    // so a click on an already-selected building still refreshes its panel.
+    void selectBuildings(const std::vector<BuildingId>& ids, SelectionMode mode);
+
+    // Selects field objects, clearing any building selection. Actors and debris are
+    // set together so a Replace can express "these actors and no debris" — which is
+    // what a plain click on an actor means — while a Toggle or Add leaves the
+    // category whose vector is empty untouched. Always publishes both field events.
+    void selectFieldObjects(const std::vector<entt::entity>& actors,
+                            const std::vector<entt::entity>& debris,
+                            SelectionMode mode);
+
+    // Empties all three categories, publishing only for those that were non-empty.
+    void clearAll();
+
+    // Replace one category outright, publishing only if it actually changed. For
+    // the per-frame prune of entities that despawned or died: the liveness query
+    // belongs to the caller, which is the one that can see the simulation.
+    void setSelectedActors(std::vector<entt::entity> actors);
+    void setSelectedDebris(std::vector<entt::entity> debris);
+
+private:
+    // Each returns whether anything changed, without publishing.
+    bool clearBuildingsQuietly();
+    bool clearActorsQuietly();
+    bool clearDebrisQuietly();
+
+    void publishBuildings() const;
+    void publishActors() const;
+    void publishDebris() const;
+
+    std::vector<BuildingId>   m_buildings;
+    std::vector<entt::entity> m_actors;
+    std::vector<entt::entity> m_debris;
+};

src/test/CMakeLists.txt

@@ -14,6 +14,7 @@ add_files(
     TunnelCompletionTest.cpp
     WorldCoordinatesTest.cpp
     WorldCameraTest.cpp
+    SelectionControllerTest.cpp
     BuildingTest.cpp
     BuildingConfigTest.cpp
     ShipTest.cpp

src/test/SelectionControllerTest.cpp

@@ -0,0 +1,282 @@
+#include "catch.hpp"
+
+#include <memory>
+#include <vector>
+
+#include "DebrisSelectionChangedEvent.h"
+#include "EntitySelectionChangedEvent.h"
+#include "EventHandler.h"
+#include "EventManager.h"
+#include "SelectionChangedEvent.h"
+#include "SelectionController.h"
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+// Counts the change events the controller publishes, so the tests can assert not
+// just the resulting selection but that the widgets were told about it — and, for
+// the categories a change did not touch, that they were not told needlessly.
+class SelectionEventSpy : public CombinedEventHandler<SelectionChangedEvent,
+                                                      EntitySelectionChangedEvent,
+                                                      DebrisSelectionChangedEvent>
+{
+public:
+    SelectionEventSpy()  { registerForEvents(); }
+    ~SelectionEventSpy() { unregisterForEvents(); }
+
+    int buildingEvents = 0;
+    int actorEvents    = 0;
+    int debrisEvents   = 0;
+
+    void reset() { buildingEvents = 0; actorEvents = 0; debrisEvents = 0; }
+
+private:
+    void handleEvent(std::shared_ptr<const SelectionChangedEvent> /*event*/) override
+    {
+        ++buildingEvents;
+    }
+    void handleEvent(std::shared_ptr<const EntitySelectionChangedEvent> /*event*/) override
+    {
+        ++actorEvents;
+    }
+    void handleEvent(std::shared_ptr<const DebrisSelectionChangedEvent> /*event*/) override
+    {
+        ++debrisEvents;
+    }
+};
+
+static entt::entity makeEntity(int index)
+{
+    return static_cast<entt::entity>(index);
+}
+
+// ---------------------------------------------------------------------------
+// Category precedence (REQ-UI-SELECTION-CATEGORIES)
+// ---------------------------------------------------------------------------
+
+TEST_CASE("Selecting a building clears actors and debris", "[selection]")
+{
+    SelectionController controller;
+    controller.selectFieldObjects({makeEntity(1)}, {makeEntity(2)},
+                                  SelectionMode::Replace);
+
+    controller.selectBuildings({BuildingId(7)}, SelectionMode::Replace);
+
+    REQUIRE(controller.getSelectedBuildings() == std::vector<BuildingId>{BuildingId(7)});
+    REQUIRE(controller.getSelectedActors().empty());
+    REQUIRE(controller.getSelectedDebris().empty());
+}
+
+TEST_CASE("Selecting a field object clears buildings", "[selection]")
+{
+    SelectionController controller;
+    controller.selectBuildings({BuildingId(7)}, SelectionMode::Replace);
+
+    controller.selectFieldObjects({makeEntity(1)}, {}, SelectionMode::Replace);
+
+    REQUIRE(controller.getSelectedBuildings().empty());
+    REQUIRE(controller.getSelectedActors() == std::vector<entt::entity>{makeEntity(1)});
+}
+
+TEST_CASE("Actors and debris coexist", "[selection]")
+{
+    // The one pair of categories that does not evict each other
+    // (REQ-UI-MULTI-SELECT, REQ-UI-DEBRIS-MULTI-SELECT).
+    SelectionController controller;
+    controller.selectFieldObjects({makeEntity(1)}, {makeEntity(2)},
+                                  SelectionMode::Replace);
+
+    REQUIRE(controller.getSelectedActors() == std::vector<entt::entity>{makeEntity(1)});
+    REQUIRE(controller.getSelectedDebris() == std::vector<entt::entity>{makeEntity(2)});
+}
+
+TEST_CASE("A plain click on an actor drops any selected debris", "[selection]")
+{
+    // A point click passes only the category it hit, so Replace with an empty
+    // debris list is what "this actor and nothing else" means
+    // (REQ-UI-ENTITY-CLICK-SELECT).
+    SelectionController controller;
+    controller.selectFieldObjects({}, {makeEntity(2)}, SelectionMode::Replace);
+
+    controller.selectFieldObjects({makeEntity(1)}, {}, SelectionMode::Replace);
+
+    REQUIRE(controller.getSelectedActors() == std::vector<entt::entity>{makeEntity(1)});
+    REQUIRE(controller.getSelectedDebris().empty());
+}
+
+// ---------------------------------------------------------------------------
+// Replace / Toggle / Add
+// ---------------------------------------------------------------------------
+
+TEST_CASE("Replace makes the hit the whole selection", "[selection]")
+{
+    SelectionController controller;
+    controller.selectBuildings({BuildingId(1), BuildingId(2)}, SelectionMode::Replace);
+
+    controller.selectBuildings({BuildingId(3)}, SelectionMode::Replace);
+
+    REQUIRE(controller.getSelectedBuildings() == std::vector<BuildingId>{BuildingId(3)});
+}
+
+TEST_CASE("Toggle adds a building that was not selected", "[selection]")
+{
+    SelectionController controller;
+    controller.selectBuildings({BuildingId(1)}, SelectionMode::Replace);
+
+    controller.selectBuildings({BuildingId(2)}, SelectionMode::Toggle);
+
+    REQUIRE(controller.getSelectedBuildings()
+            == std::vector<BuildingId>{BuildingId(1), BuildingId(2)});
+}
+
+TEST_CASE("Toggle removes a building that was already selected", "[selection]")
+{
+    // Ctrl+clicking a selected building deselects it, leaving the rest alone.
+    SelectionController controller;
+    controller.selectBuildings({BuildingId(1), BuildingId(2), BuildingId(3)},
+                               SelectionMode::Replace);
+
+    controller.selectBuildings({BuildingId(2)}, SelectionMode::Toggle);
+
+    REQUIRE(controller.getSelectedBuildings()
+            == std::vector<BuildingId>{BuildingId(1), BuildingId(3)});
+}
+
+TEST_CASE("Add never deselects", "[selection]")
+{
+    // This is where a Ctrl box drag differs from a Ctrl click: dragging over
+    // already-selected buildings must not toggle them off (REQ-UI-MULTI-SELECT).
+    SelectionController controller;
+    controller.selectBuildings({BuildingId(1), BuildingId(2)}, SelectionMode::Replace);
+
+    controller.selectBuildings({BuildingId(2), BuildingId(3)}, SelectionMode::Add);
+
+    REQUIRE(controller.getSelectedBuildings()
+            == std::vector<BuildingId>{BuildingId(1), BuildingId(2), BuildingId(3)});
+}
+
+TEST_CASE("An additive field selection leaves the untouched category alone",
+          "[selection]")
+{
+    // Ctrl+clicking an actor passes an empty debris list, which must mean "do not
+    // touch debris" rather than "clear debris" (REQ-UI-DEBRIS-MULTI-SELECT).
+    SelectionController controller;
+    controller.selectFieldObjects({}, {makeEntity(5)}, SelectionMode::Replace);
+
+    controller.selectFieldObjects({makeEntity(1)}, {}, SelectionMode::Toggle);
+
+    REQUIRE(controller.getSelectedActors() == std::vector<entt::entity>{makeEntity(1)});
+    REQUIRE(controller.getSelectedDebris() == std::vector<entt::entity>{makeEntity(5)});
+}
+
+// ---------------------------------------------------------------------------
+// Membership queries used by the renderer
+// ---------------------------------------------------------------------------
+
+TEST_CASE("Membership queries answer per category", "[selection]")
+{
+    SelectionController controller;
+    controller.selectFieldObjects({makeEntity(1)}, {makeEntity(2)},
+                                  SelectionMode::Replace);
+
+    REQUIRE(controller.isActorSelected(makeEntity(1)));
+    REQUIRE_FALSE(controller.isActorSelected(makeEntity(2)));
+    REQUIRE(controller.isDebrisSelected(makeEntity(2)));
+    REQUIRE_FALSE(controller.isDebrisSelected(makeEntity(1)));
+}
+
+// ---------------------------------------------------------------------------
+// Published events
+// ---------------------------------------------------------------------------
+
+TEST_CASE("Selecting a building announces the categories it cleared", "[selection]")
+{
+    SelectionController controller;
+    controller.selectFieldObjects({makeEntity(1)}, {makeEntity(2)},
+                                  SelectionMode::Replace);
+
+    SelectionEventSpy spy;
+    controller.selectBuildings({BuildingId(7)}, SelectionMode::Replace);
+
+    REQUIRE(spy.buildingEvents == 1);
+    REQUIRE(spy.actorEvents    == 1);
+    REQUIRE(spy.debrisEvents   == 1);
+}
+
+TEST_CASE("Clearing an already-empty category announces nothing", "[selection]")
+{
+    // The panels re-read on every event, so a redundant one is only noise — but the
+    // point-click and box paths used to disagree about this, so it is pinned.
+    SelectionController controller;
+
+    SelectionEventSpy spy;
+    controller.selectBuildings({BuildingId(7)}, SelectionMode::Replace);
+
+    REQUIRE(spy.buildingEvents == 1);
+    REQUIRE(spy.actorEvents    == 0);
+    REQUIRE(spy.debrisEvents   == 0);
+}
+
+TEST_CASE("Re-selecting the same building still announces it", "[selection]")
+{
+    // Clicking an already-selected building refreshes its panel, so the event
+    // fires even though the selection did not change.
+    SelectionController controller;
+    controller.selectBuildings({BuildingId(7)}, SelectionMode::Replace);
+
+    SelectionEventSpy spy;
+    controller.selectBuildings({BuildingId(7)}, SelectionMode::Replace);
+
+    REQUIRE(spy.buildingEvents == 1);
+}
+
+TEST_CASE("Clearing an empty selection announces nothing at all", "[selection]")
+{
+    SelectionController controller;
+
+    SelectionEventSpy spy;
+    controller.clearAll();
+
+    REQUIRE(spy.buildingEvents == 0);
+    REQUIRE(spy.actorEvents    == 0);
+    REQUIRE(spy.debrisEvents   == 0);
+}
+
+TEST_CASE("Clearing a populated selection announces every populated category",
+          "[selection]")
+{
+    SelectionController controller;
+    controller.selectFieldObjects({makeEntity(1)}, {makeEntity(2)},
+                                  SelectionMode::Replace);
+
+    SelectionEventSpy spy;
+    controller.clearAll();
+
+    REQUIRE(spy.buildingEvents == 0);  // buildings were already empty
+    REQUIRE(spy.actorEvents    == 1);
+    REQUIRE(spy.debrisEvents   == 1);
+    REQUIRE(controller.getSelectedActors().empty());
+    REQUIRE(controller.getSelectedDebris().empty());
+}
+
+// ---------------------------------------------------------------------------
+// Pruning despawned entities
+// ---------------------------------------------------------------------------
+
+TEST_CASE("Pruning announces only when something actually went", "[selection]")
+{
+    // Runs every frame, so re-announcing an unchanged selection would spam the
+    // panels 60 times a second.
+    SelectionController controller;
+    controller.selectFieldObjects({makeEntity(1), makeEntity(2)}, {},
+                                  SelectionMode::Replace);
+
+    SelectionEventSpy spy;
+    controller.setSelectedActors({makeEntity(1), makeEntity(2)});
+    REQUIRE(spy.actorEvents == 0);
+
+    controller.setSelectedActors({makeEntity(1)});
+    REQUIRE(spy.actorEvents == 1);
+    REQUIRE(controller.getSelectedActors() == std::vector<entt::entity>{makeEntity(1)});
+}

src/ui/GameWorldView.cpp

@@ -46,7 +46,6 @@
 #include "ReplayRecorder.h"
 #include "DeconstructModeChangedEvent.h"
 #include "EntityHitTest.h"
-#include "EntitySelectionChangedEvent.h"
 #include "EventManager.h"
 #include "FacingComponent.h"
 #include "FactionComponent.h"
@@ -58,7 +57,6 @@
 #include "PositionComponent.h"
 #include "RepairBehavior.h"
 #include "SalvageScrapBehavior.h"
-#include "DebrisSelectionChangedEvent.h"
 #include "DebrisSystem.h"
 #include "SelectionChangedEvent.h"
 #include "SensorRangeComponent.h"
@@ -675,51 +673,35 @@ std::optional<QVector2D> GameWorldView::entityPosition(entt::entity entity) cons
     return m_sim->getAdmin().get<PositionComponent>(entity).value;
 }
 
-void GameWorldView::clearDebrisSelection()
-{
-    if (m_selectedDebris.empty()) { return; }
-    m_selectedDebris.clear();
-    EventManager::getInstance()->sendEventImmediately(
-        std::make_shared<DebrisSelectionChangedEvent>(m_selectedDebris));
-}
-
 void GameWorldView::pruneDespawnedDebris()
 {
-    if (m_selectedDebris.empty()) { return; }
+    const std::vector<entt::entity>& selected = m_selection.getSelectedDebris();
+    if (selected.empty()) { return; }
 
+    // Keeps the debris that still exist, in the order the simulation reports them.
     std::vector<entt::entity> live;
     for (const DebrisInfo& info : getAllDebrisInfo(m_sim->getAdmin()))
     {
-        if (std::find(m_selectedDebris.begin(), m_selectedDebris.end(), info.entity)
-            != m_selectedDebris.end())
+        if (std::find(selected.begin(), selected.end(), info.entity) != selected.end())
         {
             live.push_back(info.entity);
         }
     }
 
-    if (live.size() != m_selectedDebris.size())
+    if (live.size() != selected.size())
     {
-        m_selectedDebris = std::move(live);
-        EventManager::getInstance()->sendEventImmediately(
-            std::make_shared<DebrisSelectionChangedEvent>(m_selectedDebris));
+        m_selection.setSelectedDebris(std::move(live));
     }
 }
 
-void GameWorldView::clearEntitySelection()
-{
-    if (m_selectedEntities.empty()) { return; }
-    m_selectedEntities.clear();
-    EventManager::getInstance()->sendEventImmediately(
-        std::make_shared<EntitySelectionChangedEvent>(m_selectedEntities));
-}
-
 void GameWorldView::pruneDespawnedActors()
 {
-    if (m_selectedEntities.empty()) { return; }
+    const std::vector<entt::entity>& selected = m_selection.getSelectedActors();
+    if (selected.empty()) { return; }
 
     EntityAdmin& admin = m_sim->getAdmin();
     std::vector<entt::entity> live;
-    for (entt::entity e : m_selectedEntities)
+    for (entt::entity e : selected)
     {
         if (admin.isValid(e) && admin.hasAll<HealthComponent>(e)
             && admin.get<HealthComponent>(e).hp > 0.0f)
@@ -728,18 +710,7 @@ void GameWorldView::pruneDespawnedActors()
         }
     }
 
-    if (live.size() != m_selectedEntities.size())
-    {
-        m_selectedEntities = std::move(live);
-        EventManager::getInstance()->sendEventImmediately(
-            std::make_shared<EntitySelectionChangedEvent>(m_selectedEntities));
-    }
-}
-
-bool GameWorldView::isEntitySelected(entt::entity entity) const
-{
-    return std::find(m_selectedEntities.begin(), m_selectedEntities.end(), entity)
-        != m_selectedEntities.end();
+    m_selection.setSelectedActors(std::move(live));
 }
 
 void GameWorldView::stepSpeed(int delta)
@@ -1417,7 +1388,7 @@ void GameWorldView::drawSelectionHighlights(QPainter& painter,
     painter.setPen(QPen(m_visuals->overlays.selectedOutline, 2));
     painter.setBrush(Qt::NoBrush);
 
-    for (BuildingId selId : m_selectedBuildingIds)
+    for (BuildingId selId : m_selection.getSelectedBuildings())
     {
         const std::optional<QRectF> rect = footprintWidgetRect(coordinates, selId);
         if (!rect.has_value()) { continue; }
@@ -1427,14 +1398,13 @@ void GameWorldView::drawSelectionHighlights(QPainter& painter,
 
     // A ring around each selected piece of debris, sitting just outside the debris's
     // rendered circle (radius getTilePx()*0.2, matching drawDebris) (REQ-UI-DEBRIS-CLICK-SELECT).
-    if (!m_selectedDebris.empty())
+    if (!m_selection.getSelectedDebris().empty())
     {
         const qreal outlineRadius =
             static_cast<qreal>(coordinates.getTilePx() * 0.2f) + 3.0;
         for (const DebrisInfo& debris : getAllDebrisInfo(m_sim->getAdmin()))
         {
-            if (std::find(m_selectedDebris.begin(), m_selectedDebris.end(), debris.entity)
-                == m_selectedDebris.end()) { continue; }
+            if (!m_selection.isDebrisSelected(debris.entity)) { continue; }
             painter.drawEllipse(coordinates.worldToWidget(debris.position),
                                 outlineRadius, outlineRadius);
         }
@@ -1622,7 +1592,7 @@ void GameWorldView::drawStations(QPainter& painter, const WorldCoordinates& coor
             // colored blue/red by the player/enemy fill it is drawn over.
             drawBuildingIcon(painter, coordinates, visType, bboxRect, bv.fill);
 
-            if (isEntitySelected(e))
+            if (m_selection.isActorSelected(e))
             {
                 painter.setPen(QPen(m_visuals->overlays.selectedOutline, 2));
                 painter.setBrush(Qt::NoBrush);
@@ -1670,7 +1640,7 @@ void GameWorldView::drawShips(QPainter& painter, const WorldCoordinates& coordin
             painter.setBrush(it->second.fill);
             painter.drawPolygon(tri);
 
-            if (isEntitySelected(e))
+            if (m_selection.isActorSelected(e))
             {
                 painter.setPen(QPen(m_visuals->overlays.selectedOutline, 2));
                 painter.setBrush(Qt::NoBrush);
@@ -1899,7 +1869,7 @@ void GameWorldView::drawBeams(QPainter& painter, const WorldCoordinates& coordin
 void GameWorldView::drawSelectedTunnelConnections(QPainter& painter,
                                                   const WorldCoordinates& coordinates)
 {
-    if (m_selectedBuildingIds.empty()) { return; }
+    if (m_selection.getSelectedBuildings().empty()) { return; }
 
     const TunnelTileMap tunnels = collectTunnelTiles();
     if (tunnels.empty()) { return; }
@@ -1910,7 +1880,7 @@ void GameWorldView::drawSelectedTunnelConnections(QPainter& painter,
     // (or overlapping runs) is filled exactly once — filling a semi-transparent green
     // twice would darken it (REQ-BLD-TUNNEL-SELECT-HIGHLIGHT).
     std::set<QPoint, QPointCompare> highlightTiles;
-    for (const BuildingId id : m_selectedBuildingIds)
+    for (const BuildingId id : m_selection.getSelectedBuildings())
     {
         std::optional<QPoint>   anchor;
         std::optional<BuildingType> type;
@@ -2429,128 +2399,82 @@ void GameWorldView::mousePressEvent(QMouseEvent* event)
         }
 
         const bool ctrl = (event->modifiers() & Qt::ControlModifier) != 0;
-        const QVector2D worldPos = coordinates.widgetToWorld(event->pos());
 
-        // Point hit-test precedence: buildings win over actors, which win over debris
-        // (REQ-UI-SELECTION-CATEGORIES).
-        std::optional<BuildingId> buildingHit = buildingAtTile(tile);
-        if (!buildingHit.has_value()) { buildingHit = siteAtTile(tile); }
-
-        if (buildingHit.has_value())
+        // Only a click that hit nothing starts a box drag. Starting one on a hit
+        // would re-resolve the same object as a 1x1 box on release and undo the
+        // click: a Ctrl+click would toggle the building off, then straight back on.
+        if (!selectAtPoint(tile, coordinates.widgetToWorld(event->pos()), ctrl))
         {
-            const BuildingId id = *buildingHit;
-            // A building selection is exclusive: it clears any field selection —
-            // actors and debris — because buildings win (REQ-UI-SELECTION-CATEGORIES).
-            clearEntitySelection();
-            clearDebrisSelection();
-            if (ctrl)
-            {
-                bool found = false;
-                std::vector<BuildingId> newSel;
-                for (BuildingId sel : m_selectedBuildingIds)
-                {
-                    if (sel == id) { found = true; }
-                    else           { newSel.push_back(sel); }
-                }
-                if (!found) { newSel.push_back(id); }
-                m_selectedBuildingIds = newSel;
-            }
-            else
-            {
-                m_selectedBuildingIds = { id };
-            }
-            EventManager::getInstance()->sendEventImmediately(
-                std::make_shared<SelectionChangedEvent>(m_selectedBuildingIds));
-            return;
-        }
-
-        // Selecting a field object (actor or debris) clears any building selection but
-        // lets actors and debris coexist (REQ-UI-SELECTION-CATEGORIES).
-        const entt::entity actorHit = entityAtWorldPos(m_sim->getAdmin(), worldPos);
-        if (actorHit != entt::null)
-        {
-            if (!m_selectedBuildingIds.empty())
-            {
-                m_selectedBuildingIds.clear();
-                EventManager::getInstance()->sendEventImmediately(
-                    std::make_shared<SelectionChangedEvent>(m_selectedBuildingIds));
-            }
-            if (ctrl)
-            {
-                // Toggle this actor within the field selection, leaving debris intact
-                // (REQ-UI-ENTITY-CLICK-SELECT).
-                bool found = false;
-                std::vector<entt::entity> newSel;
-                for (entt::entity sel : m_selectedEntities)
-                {
-                    if (sel == actorHit) { found = true; }
-                    else                 { newSel.push_back(sel); }
-                }
-                if (!found) { newSel.push_back(actorHit); }
-                m_selectedEntities = newSel;
-            }
-            else
-            {
-                // A plain click makes this actor the sole selection.
-                m_selectedEntities = { actorHit };
-                clearDebrisSelection();
-            }
-            EventManager::getInstance()->sendEventImmediately(
-                std::make_shared<EntitySelectionChangedEvent>(m_selectedEntities));
-            return;
-        }
-
-        if (const entt::entity debrisHit =
-                debrisAtWorldPos(m_sim->getAdmin(), worldPos); debrisHit != entt::null)
-        {
-            if (!m_selectedBuildingIds.empty())
-            {
-                m_selectedBuildingIds.clear();
-                EventManager::getInstance()->sendEventImmediately(
-                    std::make_shared<SelectionChangedEvent>(m_selectedBuildingIds));
-            }
-            if (ctrl)
-            {
-                // Toggle this debris within the field selection, leaving actors intact
-                // (REQ-UI-DEBRIS-MULTI-SELECT).
-                bool found = false;
-                std::vector<entt::entity> newSel;
-                for (entt::entity sel : m_selectedDebris)
-                {
-                    if (sel == debrisHit) { found = true; }
-                    else                 { newSel.push_back(sel); }
-                }
-                if (!found) { newSel.push_back(debrisHit); }
-                m_selectedDebris = newSel;
-            }
-            else
-            {
-                // A plain click makes this debris the sole selection.
-                m_selectedDebris = { debrisHit };
-                clearEntitySelection();
-            }
-            EventManager::getInstance()->sendEventImmediately(
-                std::make_shared<DebrisSelectionChangedEvent>(m_selectedDebris));
-            return;
-        }
-
-        // Empty space: a plain click clears the whole selection and starts a box drag;
-        // Ctrl preserves the current selection for additive box-select.
-        if (!ctrl)
-        {
-            if (!m_selectedBuildingIds.empty())
-            {
-                m_selectedBuildingIds.clear();
-                EventManager::getInstance()->sendEventImmediately(
-                    std::make_shared<SelectionChangedEvent>(m_selectedBuildingIds));
-            }
-            clearEntitySelection();
-            clearDebrisSelection();
-        }
+            // selectAtPoint has already cleared the selection unless Ctrl is
+            // preserving it for an additive drag.
             m_boxSelecting    = true;
             m_boxStartTile    = tile;
             m_boxCurrentTile  = tile;
         }
+    }
+}
+
+bool GameWorldView::selectAtPoint(QPoint tile, QVector2D worldPos, bool additive)
+{
+    // Point hit-test precedence: buildings win over actors, which win over debris
+    // (REQ-UI-SELECTION-CATEGORIES). What each hit then does to the existing
+    // selection is the controller's business, not this method's.
+    const SelectionMode mode = additive ? SelectionMode::Toggle : SelectionMode::Replace;
+
+    std::optional<BuildingId> buildingHit = buildingAtTile(tile);
+    if (!buildingHit.has_value()) { buildingHit = siteAtTile(tile); }
+    if (buildingHit.has_value())
+    {
+        m_selection.selectBuildings({*buildingHit}, mode);
+        return true;
+    }
+
+    const entt::entity actorHit = entityAtWorldPos(m_sim->getAdmin(), worldPos);
+    if (actorHit != entt::null)
+    {
+        m_selection.selectFieldObjects({actorHit}, {}, mode);
+        return true;
+    }
+
+    const entt::entity debrisHit = debrisAtWorldPos(m_sim->getAdmin(), worldPos);
+    if (debrisHit != entt::null)
+    {
+        m_selection.selectFieldObjects({}, {debrisHit}, mode);
+        return true;
+    }
+
+    // Empty space: a plain click clears the whole selection, Ctrl preserves it.
+    if (!additive) { m_selection.clearAll(); }
+    return false;
+}
+
+void GameWorldView::selectInBox(bool additive)
+{
+    // Same precedence as a point click, over everything the box covers
+    // (REQ-UI-MULTI-SELECT, REQ-UI-DEBRIS-MULTI-SELECT). The only difference is the
+    // mode: a Ctrl box adds and never deselects, where a Ctrl click toggles.
+    const SelectionMode mode = additive ? SelectionMode::Add : SelectionMode::Replace;
+
+    const std::vector<BuildingId> boxIds =
+        buildingsInBox(m_boxStartTile, m_boxCurrentTile);
+    if (!boxIds.empty())
+    {
+        m_selection.selectBuildings(boxIds, mode);
+        return;
+    }
+
+    const std::vector<entt::entity> boxActors =
+        actorsInBox(m_sim->getAdmin(), m_boxStartTile, m_boxCurrentTile);
+    const std::vector<entt::entity> boxDebris =
+        debrisInBox(m_sim->getAdmin(), m_boxStartTile, m_boxCurrentTile);
+    if (!boxActors.empty() || !boxDebris.empty())
+    {
+        m_selection.selectFieldObjects(boxActors, boxDebris, mode);
+        return;
+    }
+
+    // Empty box: a plain (non-additive) drag clears the current selection.
+    if (!additive) { m_selection.clearAll(); }
 }
 
 void GameWorldView::mouseMoveEvent(QMouseEvent* event)
@@ -2675,91 +2599,7 @@ void GameWorldView::mouseReleaseEvent(QMouseEvent* event)
             return;
         }
 
-        const bool ctrl = (event->modifiers() & Qt::ControlModifier) != 0;
-
-        if (!boxIds.empty())
-        {
-            // A box covering any building selects buildings; field objects (actors and
-            // debris) in the box are ignored — buildings win (REQ-UI-MULTI-SELECT).
-            clearEntitySelection();
-            clearDebrisSelection();
-            if (!ctrl)
-            {
-                m_selectedBuildingIds = boxIds;
-            }
-            else
-            {
-                for (BuildingId id : boxIds)
-                {
-                    bool found = false;
-                    for (BuildingId sel : m_selectedBuildingIds)
-                    {
-                        if (sel == id) { found = true; break; }
-                    }
-                    if (!found) { m_selectedBuildingIds.push_back(id); }
-                }
-            }
-            EventManager::getInstance()->sendEventImmediately(
-                std::make_shared<SelectionChangedEvent>(m_selectedBuildingIds));
-            return;
-        }
-
-        // No buildings in the box: select the field objects it covers — ships, defence
-        // stations, and debris together (REQ-UI-MULTI-SELECT, REQ-UI-DEBRIS-MULTI-SELECT).
-        const std::vector<entt::entity> boxActors =
-            actorsInBox(m_sim->getAdmin(), m_boxStartTile, m_boxCurrentTile);
-        const std::vector<entt::entity> boxDebris =
-            debrisInBox(m_sim->getAdmin(), m_boxStartTile, m_boxCurrentTile);
-        if (!boxActors.empty() || !boxDebris.empty())
-        {
-            if (!m_selectedBuildingIds.empty())
-            {
-                m_selectedBuildingIds.clear();
-                EventManager::getInstance()->sendEventImmediately(
-                    std::make_shared<SelectionChangedEvent>(m_selectedBuildingIds));
-            }
-            if (!ctrl)
-            {
-                m_selectedEntities = boxActors;
-                m_selectedDebris    = boxDebris;
-            }
-            else
-            {
-                for (entt::entity e : boxActors)
-                {
-                    bool found = false;
-                    for (entt::entity sel : m_selectedEntities)
-                    {
-                        if (sel == e) { found = true; break; }
-                    }
-                    if (!found) { m_selectedEntities.push_back(e); }
-                }
-                for (entt::entity e : boxDebris)
-                {
-                    bool found = false;
-                    for (entt::entity sel : m_selectedDebris)
-                    {
-                        if (sel == e) { found = true; break; }
-                    }
-                    if (!found) { m_selectedDebris.push_back(e); }
-                }
-            }
-            EventManager::getInstance()->sendEventImmediately(
-                std::make_shared<EntitySelectionChangedEvent>(m_selectedEntities));
-            EventManager::getInstance()->sendEventImmediately(
-                std::make_shared<DebrisSelectionChangedEvent>(m_selectedDebris));
-            return;
-        }
-
-        // Empty box: a plain (non-additive) drag clears the current selection.
-        if (!ctrl)
-        {
-            m_selectedBuildingIds.clear();
-            EventManager::getInstance()->sendEventImmediately(
-                std::make_shared<SelectionChangedEvent>(m_selectedBuildingIds));
-            clearEntitySelection();
-            clearDebrisSelection();
-        }
+        selectInBox((event->modifiers() & Qt::ControlModifier) != 0);
     }
 }
 
@@ -2978,9 +2818,7 @@ void GameWorldView::resetForNewGame()
     m_deconstructHoverBuildingId  = std::nullopt;
     EventManager::getInstance()->sendEventImmediately(
         std::make_shared<DeconstructModeChangedEvent>(false));
-    m_selectedBuildingIds.clear();
-    clearEntitySelection();
-    clearDebrisSelection();
+    m_selection.clearAll();
     m_copiedConfig     = std::nullopt;
     m_copyConfigFlashes.clear();
     m_boxSelecting     = false;

src/ui/GameWorldView.h

@@ -52,6 +52,7 @@
 #include "EntitySelectionChangedEvent.h"
 #include "GameConfig.h"
 #include "Rotation.h"
+#include "SelectionController.h"
 #include "Tick.h"
 #include "TickDriver.h"
 #include "TunnelCompletion.h"
@@ -247,21 +248,18 @@ private:
     void     placeBlueprintAtTile(QPoint center);
 
     std::optional<QVector2D> entityPosition(entt::entity entity) const;
-    // Clears the debris selection, emitting an empty DebrisSelectionChangedEvent when
-    // it was non-empty (REQ-UI-DEBRIS-CLICK-SELECT). Used when another selection
-    // category takes over.
-    void                     clearDebrisSelection();
-    // Drops despawned or fully-collected debris from the selection and re-emits
-    // when it changed (REQ-UI-DEBRIS-CLICK-SELECT). Called each frame from onFrame().
+    // Drops despawned or fully-collected debris from the selection
+    // (REQ-UI-DEBRIS-CLICK-SELECT). Called each frame from onFrame().
     void                     pruneDespawnedDebris();
-    // Clears the actor selection, emitting an empty EntitySelectionChangedEvent when it was
-    // non-empty (REQ-UI-ENTITY-CLICK-SELECT). Used when buildings take over.
-    void                     clearEntitySelection();
-    // Drops despawned or dead actors from the selection and re-emits when it changed
-    // (REQ-UI-ENTITY-CLICK-SELECT). Called each frame from onFrame().
+    // Drops despawned or dead actors from the selection (REQ-UI-ENTITY-CLICK-SELECT).
+    // Called each frame from onFrame().
     void                     pruneDespawnedActors();
-    // True if the given actor is part of the current actor selection.
-    bool                     isEntitySelected(entt::entity entity) const;
+    // Resolves a click into the selection it should produce, applying the category
+    // precedence of REQ-UI-SELECTION-CATEGORIES; the controller owns what that then
+    // does to the existing selection. Returns false when the click hit nothing,
+    // which is the only case that goes on to start a box drag.
+    bool                     selectAtPoint(QPoint tile, QVector2D worldPos, bool additive);
+    void                     selectInBox(bool additive);
     void                     stepSpeed(int delta);
     void                     placeAtTile(QPoint tile);
 
@@ -410,9 +408,10 @@ private:
     std::optional<BuildingId> m_deconstructHoverBuildingId;
     bool     m_debugDraw;
 
-    std::vector<BuildingId> m_selectedBuildingIds;
-    std::vector<entt::entity> m_selectedEntities;
-    std::vector<entt::entity> m_selectedDebris;
+    // Owns the selection across all three categories and the rules for moving
+    // between them (REQ-UI-SELECTION-CATEGORIES), including publishing the change
+    // events. This widget only resolves what was hit.
+    SelectionController   m_selection;
     bool                  m_boxSelecting;
     QPoint                m_boxStartTile;
     QPoint                m_boxCurrentTile;