show recipes visually instead of describing them in text

src/ui/selection/ItemTooltip.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include <string>
+
+#include <QFrame>
+
+#include "SelectionContext.h"
+
+class QVBoxLayout;
+
+// The tooltip an item chip shows on hover: the item's name, and every way the player
+// can currently produce it, each drawn as a recipe line (REQ-UI-ITEM-TOOLTIP).
+//
+// A window of its own rather than a Qt tooltip, because Qt's are text and this one is
+// drawn -- item squares, building chips and all. It is a Qt::ToolTip window, so it
+// floats above everything and takes no input.
+class ItemTooltip : public QFrame
+{
+    Q_OBJECT
+
+public:
+    ItemTooltip(const SelectionContext& context, const std::string& itemId,
+                QWidget* parent = nullptr);
+
+    // Rebuilds the content and shows the tooltip near the given screen position, kept
+    // inside the screen. Rebuilt on every show because what produces an item changes as
+    // the player unlocks recipes (REQ-LOCK-UI-RECIPE).
+    void showAt(const QPoint& globalPos);
+
+private:
+    void rebuild();
+
+    SelectionContext m_context;
+    std::string      m_itemId;
+    QVBoxLayout*     m_layout;
+};