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

mario/blocks.cpp

@@ -656,3 +656,12 @@ void MarioBlock::setBaseRect(SDL_Rect rect) {
     _base_src = rect;
     setType(getType());
 }
+void MarioBlock::checkVisibility(double rightmost_x) {
+    // we assume that object's X > 0 as otherwise it would be destroyed
+    if(!getHidden() && getAbsolutePos().getX() < rightmost_x) {
+        _was_visible = true;
+    }
+}
+bool MarioBlock::wasVisible() const {
+    return _was_visible;
+}