Added missing setActive virtual method to sf::RenderTarget, added setActive calls to OpenGL example to demonstrate proper explicit context management.

include/SFML/Graphics/RenderWindow.hpp

@@ -112,6 +112,24 @@ public:
     ////////////////////////////////////////////////////////////
     virtual Vector2u getSize() const;
 
+    ////////////////////////////////////////////////////////////
+    /// \brief Activate or deactivate the window as the current target
+    ///        for OpenGL rendering
+    ///
+    /// A window is active only on the current thread, if you want to
+    /// make it active on another thread you have to deactivate it
+    /// on the previous thread first if it was active.
+    /// Only one window can be active on a thread at a time, thus
+    /// the window previously active (if any) automatically gets deactivated.
+    /// This is not to be confused with requestFocus().
+    ///
+    /// \param active True to activate, false to deactivate
+    ///
+    /// \return True if operation was successful, false otherwise
+    ///
+    ////////////////////////////////////////////////////////////
+    bool setActive(bool active = true);
+
     ////////////////////////////////////////////////////////////
     /// \brief Copy the current contents of the window to an image
     ///
@@ -159,18 +177,6 @@ protected:
     ///
     ////////////////////////////////////////////////////////////
     virtual void onResize();
-
-private:
-
-    ////////////////////////////////////////////////////////////
-    /// \brief Activate the target for rendering
-    ///
-    /// \param active True to make the target active, false to deactivate it
-    ///
-    /// \return True if the function succeeded
-    ///
-    ////////////////////////////////////////////////////////////
-    virtual bool activate(bool active);
 };
 
 } // namespace sf