upgrade emitters garbage collection

src/graphics/render/Emitter.hpp

@@ -54,6 +54,9 @@ class Emitter {
 
     util::PseudoRandom random;
 public:
+    /// @brief Number of references (alive particles)
+    int refCount = 0;
+    /// @brief Particle settings
     ParticlesPreset preset;
 
     Emitter(
@@ -86,6 +89,9 @@ public:
     /// @return true if the emitter has spawned all particles
     bool isDead() const;
 
+    /// @return true if there is at least one alive referring particle left
+    bool isReferred() const;
+
     const EmitterOrigin& getOrigin() const;
 
     void setOrigin(const EmitterOrigin& origin);