Show building_block icon in header stock, expand button and build costs

src/ui/BuildButtonGrid.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <map>
+#include <memory>
 #include <optional>
 #include <string>
 #include <vector>
@@ -18,6 +19,7 @@
 
 class QPushButton;
 class Simulation;
+class ItemIconCache;
 
 class BuildButtonGrid : public QWidget,
                         public CombinedEventHandler<BuilderModeExitedEvent,
@@ -30,9 +32,12 @@ class BuildButtonGrid : public QWidget,
 
 public:
     // iconDir is the directory holding the per-building "<id>.svg" chip icons
-    // (REQ-UI-BUILD-GRID); read from disk at runtime, like the config files.
+    // (REQ-UI-BUILD-GRID); itemsIconDir holds the per-item icons and supplies the
+    // building_block icon shown in each button's cost (REQ-UI-BUILD-COST). Both are
+    // read from disk at runtime, like the config files.
     BuildButtonGrid(Simulation* sim, const GameConfig* config,
-                    const std::string& iconDir, QWidget* parent = nullptr);
+                    const std::string& iconDir, const std::string& itemsIconDir,
+                    QWidget* parent = nullptr);
     ~BuildButtonGrid() override;
 
     void clearActiveButton();
@@ -60,6 +65,7 @@ private:
     Simulation*                      m_sim;
     const GameConfig*                m_config;
     std::string                      m_iconDir;
+    std::unique_ptr<ItemIconCache>   m_itemIcons;
     std::vector<BuildingType>        m_types;
     std::vector<QPushButton*>        m_buttons;
     std::map<BuildingType, int>      m_costs;