Implement config-driven unlock groups so that multiple things can be unlocked at once (including buildings)

src/ui/BuildButtonGrid.cpp

@@ -82,6 +82,7 @@ BuildButtonGrid::BuildButtonGrid(Simulation* sim, const GameConfig* config, QWid
             std::make_shared<DemolishModeToggleRequestedEvent>());
     });
 
+    updateVisibility();
     registerForEvents();
 }
 
@@ -119,6 +120,17 @@ void BuildButtonGrid::updateAffordability()
     }
 }
 
+void BuildButtonGrid::updateVisibility()
+{
+    // A locked building type's button is hidden until its unlock group is awarded
+    // (REQ-LOCK-BUILDING). Buttons keep their index so hotkeys/affordability stay
+    // stable; they simply appear once the type is unlocked.
+    for (std::size_t i = 0; i < m_buttons.size(); ++i)
+    {
+        m_buttons[i]->setVisible(m_sim->isBuildingUnlocked(m_types[i]));
+    }
+}
+
 void BuildButtonGrid::clearActiveButton()
 {
     if (m_activeIndex)
@@ -165,6 +177,12 @@ void BuildButtonGrid::handleEvent(std::shared_ptr<const BuildingBlocksChangedEve
     updateAffordability();
 }
 
+void BuildButtonGrid::handleEvent(std::shared_ptr<const UnlockedBuildingsChangedEvent> /*event*/)
+{
+    updateVisibility();
+    updateAffordability();
+}
+
 void BuildButtonGrid::handleEvent(std::shared_ptr<const DemolishModeChangedEvent> event)
 {
     m_demolishButton->setChecked(event->active);
@@ -176,9 +194,10 @@ void BuildButtonGrid::handleEvent(std::shared_ptr<const BuildHotkeyPressedEvent>
     {
         if (m_types[i] == event->type)
         {
-            // Equivalent to clicking the build button: a disabled (unaffordable)
-            // button cannot be clicked, so the hotkey is likewise inert.
-            if (m_buttons[i]->isEnabled())
+            // Equivalent to clicking the build button: a disabled (unaffordable) or
+            // hidden (locked, REQ-LOCK-BUILDING) button cannot be clicked, so the
+            // hotkey is likewise inert.
+            if (m_buttons[i]->isEnabled() && m_buttons[i]->isVisible())
             {
                 onBuildButton(static_cast<int>(i));
             }