Mario: only visit objects if they entered screen at least once

mario/blocks.hpp

@@ -42,6 +42,8 @@ public:
     bool isBouncing() const;
     bool isTraveling() const;
     void setBaseRect(SDL_Rect rect);
+    void checkVisibility(double rightmost_x);
+    bool wasVisible() const;
 
 protected:
     double bounce_speed = 0.5;
@@ -83,6 +85,7 @@ private:
     int _base_gravity_ticks = 1000 / 60;
     int _ticks_till_gravity = 0;
     double _gravity_acceleration = 1.0/(64.0/7.0);
+    bool _was_visible = false;
 };
 
 extern const std::vector< uint64_t > possibleBlocks;