implement demolish button

src/ui/BuildButtonGrid.cpp

@@ -82,6 +82,12 @@ BuildButtonGrid::BuildButtonGrid(const GameConfig* config, QWidget* parent)
         }
     }
     connect(mapper, SIGNAL(mapped(int)), this, SLOT(onBuildButton(int)));
+
+    m_demolishButton = new QPushButton("Demolish", this);
+    m_demolishButton->setCheckable(true);
+    m_demolishButton->setFixedHeight(48);
+    layout->addWidget(m_demolishButton, row, col);
+    connect(m_demolishButton, SIGNAL(clicked()), this, SIGNAL(demolishModeToggleRequested()));
 }
 
 void BuildButtonGrid::updateAffordability(int buildingBlocks)
@@ -95,6 +101,11 @@ void BuildButtonGrid::updateAffordability(int buildingBlocks)
     }
 }
 
+void BuildButtonGrid::setDemolishModeActive(bool active)
+{
+    m_demolishButton->setChecked(active);
+}
+
 void BuildButtonGrid::clearActiveButton()
 {
     if (m_activeIndex >= 0 && m_activeIndex < static_cast<int>(m_buttons.size()))

src/ui/BuildButtonGrid.h

@@ -23,6 +23,10 @@ public:
 signals:
     void buildingTypeSelected(BuildingType type);
     void builderModeExited();
+    void demolishModeToggleRequested();
+
+public slots:
+    void setDemolishModeActive(bool active);
 
 private slots:
     void onBuildButton(int index);
@@ -33,4 +37,5 @@ private:
     std::vector<QPushButton*>        m_buttons;
     std::map<BuildingType, int>      m_costs;
     int                              m_activeIndex;
+    QPushButton*                     m_demolishButton;
 };

src/ui/GameWorldView.cpp

@@ -901,16 +901,7 @@ void GameWorldView::keyPressEvent(QKeyEvent* event)
         emit escapeMenuRequested();
         break;
     case Qt::Key_Backspace:
-        if (m_demolishMode)
+        toggleDemolishMode();
-        {
-            m_demolishMode    = false;
-            m_demolishHoverId = kInvalidEntityId;
-        }
-        else
-        {
-            if (m_builderType.has_value()) { exitBuilderMode(); }
-            m_demolishMode = true;
-        }
         break;
     default:
         QOpenGLWidget::keyPressEvent(event);
@@ -1090,12 +1081,28 @@ void GameWorldView::mouseReleaseEvent(QMouseEvent* event)
 // Slots
 // ---------------------------------------------------------------------------
 
+void GameWorldView::toggleDemolishMode()
+{
+    if (m_demolishMode)
+    {
+        m_demolishMode    = false;
+        m_demolishHoverId = kInvalidEntityId;
+    }
+    else
+    {
+        if (m_builderType.has_value()) { exitBuilderMode(); }
+        m_demolishMode = true;
+    }
+    emit demolishModeChanged(m_demolishMode);
+}
+
 void GameWorldView::enterBuilderMode(BuildingType type)
 {
     m_builderType   = type;
     m_ghostRotation = Rotation::East;
     m_ghostValid    = false;
     m_demolishMode  = false;
+    emit demolishModeChanged(false);
 }
 
 void GameWorldView::exitBuilderMode()
@@ -1128,6 +1135,7 @@ void GameWorldView::resetForNewGame()
     m_ghostValid       = false;
     m_demolishMode     = false;
     m_demolishHoverId  = kInvalidEntityId;
+    emit demolishModeChanged(false);
     m_selectedIds.clear();
     m_boxSelecting     = false;
     m_scrollXTiles     = 0.0f;

src/ui/GameWorldView.h

@@ -47,6 +47,7 @@ signals:
     void gameOver();
     void builderModeExited();
     void escapeMenuRequested();
+    void demolishModeChanged(bool active);
 
 public:
     double gameSpeed() const;
@@ -54,6 +55,7 @@ public:
 public slots:
     void enterBuilderMode(BuildingType type);
     void exitBuilderMode();
+    void toggleDemolishMode();
     void setGameSpeed(double multiplier);
     void resetForNewGame();
 

src/ui/MainWindow.cpp

@@ -65,6 +65,12 @@ MainWindow::MainWindow(Simulation* sim, const GameConfig* config,
     connect(m_gameWorldView, SIGNAL(builderModeExited()),
             m_buildButtonGrid, SLOT(clearActiveButton()));
 
+    connect(m_buildButtonGrid, SIGNAL(demolishModeToggleRequested()),
+            m_gameWorldView, SLOT(toggleDemolishMode()));
+
+    connect(m_gameWorldView, SIGNAL(demolishModeChanged(bool)),
+            m_buildButtonGrid, SLOT(setDemolishModeActive(bool)));
+
     // Signals: header bar → game world
     connect(m_headerBar, SIGNAL(speedChanged(double)),
             m_gameWorldView, SLOT(setGameSpeed(double)));