[rframe] ensure RFrame is created when adding RDrawable

Some RDrawable may require RFrame, therefore when such drawable add to
the pad, automatically RFrame will be created

graf2d/gpadv7/inc/ROOT/RDrawable.hxx

@@ -98,14 +98,14 @@ public:
 
 class RDrawable {
 
-friend class RPadBase; // to access Display method
+friend class RPadBase; // to access Display method and IsFrameRequired
 friend class RAttrBase;
 friend class RStyle;
 friend class RLegend; // to access CollectShared method
 
 private:
    RAttrMap fAttr;               ///< attributes values
-   std::weak_ptr<RStyle> fStyle; ///<! style applied for RDrawable
+   std::weak_ptr<RStyle> fStyle; ///<! style applied for RDrawable, not stored when canvas is saved
    std::string fCssType;         ///<! drawable type, not stored in the root file, must be initialized in constructor
    std::string fCssClass;        ///< user defined drawable class, can later go inside map
    std::string fId;              ///< optional object identifier, may be used in CSS as well
@@ -114,6 +114,8 @@ protected:
 
    virtual void CollectShared(Internal::RIOSharedVector_t &) {}
 
+   virtual bool IsFrameRequired() const { return false; }
+
    RAttrMap &GetAttrMap() { return fAttr; }
    const RAttrMap &GetAttrMap() const { return fAttr; }
 

graf2d/gpadv7/inc/ROOT/RPadBase.hxx

@@ -50,6 +50,12 @@ private:
    /// Disable assignment.
    RPadBase &operator=(const RPadBase &) = delete;
 
+   void TestIfFrameRequired(const RDrawable *drawable)
+   {
+      if (drawable->IsFrameRequired())
+         GetOrCreateFrame();
+   }
+
 protected:
    /// Allow derived classes to default construct a RPadBase.
    RPadBase() : RDrawable("pad") {}
@@ -79,6 +85,8 @@ public:
    {
       auto drawable = std::make_shared<T>(args...);
 
+      TestIfFrameRequired(drawable.get());
+
       fPrimitives.emplace_back(drawable);
 
       return drawable;
@@ -87,20 +95,24 @@ public:
    /// Add existing drawable instance to canvas
    auto Draw(std::shared_ptr<RDrawable> &&drawable)
    {
+      TestIfFrameRequired(drawable.get());
+
       fPrimitives.emplace_back(std::move(drawable));
 
       return fPrimitives.back().get_shared();
    }
 
-   /// Add something to be painted.
-   /// The pad observes what's lifetime through a weak pointer.
-   /// Drawing options will be constructed through `args`, which can be empty for default-constructed options.
+   /// Add object to be painted.
+   /// Correspondent drawable will be created via GetDrawable() function which should be defined and be accessed at calling time.
+   /// If required, extra arguments for GetDrawable() function can be provided.
    template <class T, class... ARGS>
    auto Draw(const std::shared_ptr<T> &what, ARGS... args)
    {
       // Requires GetDrawable(what) to be known!
       auto drawable = GetDrawable(what, args...);
 
+      TestIfFrameRequired(drawable.get());
+
       fPrimitives.emplace_back(drawable);
 
       return drawable;

graf2d/primitivesv7/inc/ROOT/RFrameTitle.hxx

@@ -28,7 +28,7 @@ namespace Experimental {
 */
 
 
-class RFrameTitle : public RDrawable {
+class RFrameTitle final : public RDrawable {
 
    class RTitleAttrs : public RAttrBase {
       friend class RFrameTitle;
@@ -39,6 +39,10 @@ class RFrameTitle : public RDrawable {
    RAttrText  fAttrText{this, "text_"};  ///<! text attributes
    RTitleAttrs fAttr{this,""};           ///<! title direct attributes
 
+protected:
+
+   bool IsFrameRequired() const final { return true; }
+
 public:
 
    RFrameTitle() : RDrawable("title") {}

hist/histdrawv7/inc/ROOT/RHistDrawable.hxx

@@ -49,6 +49,8 @@ protected:
 
    void CollectShared(Internal::RIOSharedVector_t &vect) final { vect.emplace_back(&fHistImpl); }
 
+   bool IsFrameRequired() const final { return true; }
+
 public:
    RHistDrawable();
    virtual ~RHistDrawable() = default;

tutorials/v7/draw_frame.cxx

@@ -22,6 +22,7 @@
 #include "ROOT/RFrame.hxx"
 #include "ROOT/RHistDrawable.hxx"
 #include "ROOT/RStyle.hxx"
+#include "ROOT/RPad.hxx"
 
 // macro must be here while cling is not capable to load
 // library automatically for outlined function see ROOT-10336