use handler for context menu callback

src/celestia/celestiacore.cpp

@@ -687,8 +687,8 @@ void CelestiaCore::mouseButtonUp(float x, float y, int button)
             Selection sel = sim->pickObject(pickRay, renderer->getRenderFlags(), pickTolerance);
             if (!sel.empty())
             {
-                if (contextMenuCallback != nullptr)
-                    contextMenuCallback(x, y, sel);
+                if (contextMenuHandler != nullptr)
+                    contextMenuHandler->requestContextMenu(x, y, sel);
             }
         }
         else if (button == MiddleButton)
@@ -2721,12 +2721,6 @@ void CelestiaCore::setActiveFrameVisible(bool visible)
 }
 
 
-void CelestiaCore::setContextMenuCallback(ContextMenuFunc callback)
-{
-    contextMenuCallback = callback;
-}
-
-
 Renderer* CelestiaCore::getRenderer() const
 {
     return renderer;
@@ -4490,6 +4484,16 @@ CelestiaCore::CursorHandler* CelestiaCore::getCursorHandler() const
     return cursorHandler;
 }
 
+void CelestiaCore::setContextMenuHandler(ContextMenuHandler* handler)
+{
+    contextMenuHandler = handler;
+}
+
+CelestiaCore::ContextMenuHandler* CelestiaCore::getContextMenuHandler() const
+{
+    return contextMenuHandler;
+}
+
 int CelestiaCore::getTimeZoneBias() const
 {
     return timeZoneBias;

src/celestia/celestiacore.h

@@ -197,8 +197,6 @@ class CelestiaCore // : public Watchable<CelestiaCore>
         ShowFrame     = 0x010,
     };
 
-    typedef void (*ContextMenuFunc)(float, float, Selection);
-
  private:
     class OverlayImage
     {
@@ -317,8 +315,6 @@ class CelestiaCore // : public Watchable<CelestiaCore>
     int getOverlayElements() const;
     void setOverlayElements(int);
 
-    void setContextMenuCallback(ContextMenuFunc);
-
     void addWatcher(CelestiaWatcher*);
     void removeWatcher(CelestiaWatcher*);
 
@@ -372,6 +368,16 @@ class CelestiaCore // : public Watchable<CelestiaCore>
     void setCursorHandler(CursorHandler*);
     CursorHandler* getCursorHandler() const;
 
+    class ContextMenuHandler
+    {
+    public:
+        virtual ~ContextMenuHandler() = default;
+        virtual void requestContextMenu(float, float, Selection) = 0;
+    };
+
+    void setContextMenuHandler(ContextMenuHandler*);
+    ContextMenuHandler* getContextMenuHandler() const;
+
     void toggleReferenceMark(const std::string& refMark, Selection sel = Selection());
     bool referenceMarkEnabled(const std::string& refMark, Selection sel = Selection()) const;
 
@@ -485,14 +491,13 @@ class CelestiaCore // : public Watchable<CelestiaCore>
     MovieCapture* movieCapture{ nullptr };
     bool recording{ false };
 
-    ContextMenuFunc contextMenuCallback{ nullptr };
-
     Texture* logoTexture{ nullptr };
 
     Alerter* alerter{ nullptr };
     std::vector<CelestiaWatcher*> watchers;
     CursorHandler* cursorHandler{ nullptr };
     CursorShape defaultCursorShape{ CelestiaCore::CrossCursor };
+    ContextMenuHandler* contextMenuHandler{ nullptr };
 
     std::vector<Url*> history;
     std::vector<Url*>::size_type historyCurrent{ 0 };