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

src/ui/HeaderBar.h

@@ -1,7 +1,10 @@
 #pragma once
 
+#include <memory>
+#include <string>
 #include <vector>
 
+#include <QPixmap>
 #include <QWidget>
 
 #include "ArtifactCountChangedEvent.h"
@@ -16,6 +19,7 @@
 
 class QLabel;
 class QPushButton;
+class ItemIconCache;
 
 class HeaderBar : public QWidget,
                   public CombinedEventHandler<TickAdvancedEvent,
@@ -28,7 +32,11 @@ class HeaderBar : public QWidget,
     Q_OBJECT
 
 public:
-    explicit HeaderBar(const GameConfig* config, QWidget* parent = nullptr);
+    // itemsIconDir holds the per-item icon SVGs (REQ-UI-ITEM-ICON); used to show the
+    // building_block icon in the stock display and expand button (REQ-UI-BLOCKS-ICON,
+    // REQ-UI-EXPAND-BUTTON).
+    HeaderBar(const GameConfig* config, const std::string& itemsIconDir,
+              QWidget* parent = nullptr);
     ~HeaderBar() override;
 
 private slots:
@@ -46,6 +54,15 @@ private:
     // expansion cost and building block stock (REQ-UI-EXPAND-BUTTON).
     void updateExpandButton();
 
+    // Refreshes the building blocks stock display from m_blocks: `Stock: <n>` with
+    // the building_block icon after it, or the `Stock: <n> Blocks` text fallback when
+    // no icon file exists (REQ-UI-BLOCKS-ICON).
+    void updateBlocksLabel();
+
+    // The building_block icon at the header's text height, or a null pixmap when no
+    // icon file exists. Loaded once via m_itemIcons on first use.
+    QPixmap blockIcon() const;
+
     QLabel*                  m_timeLabel;
     QLabel*                  m_blocksLabel;
     QLabel*                  m_artifactsLabel;
@@ -53,6 +70,8 @@ private:
     QPushButton*             m_expandButton;
     std::vector<QPushButton*> m_speedButtons;
 
+    std::unique_ptr<ItemIconCache> m_itemIcons;
+
     int                      m_blocks        = 0;
     int                      m_expansionCost = 0;