added ability for particle system to perform a 'soft stop' where the birthing is effectively stopped while the rest of the system runs down

panda/src/particlesystem/particleSystem.I

@@ -38,7 +38,7 @@ render() {
 
 INLINE void ParticleSystem::
 induce_labor() {
-  _tics_since_birth = _birth_rate;
+  _tics_since_birth = _cur_birth_rate;
 }
 
 ////////////////////////////////////////////////////////////////////
@@ -62,6 +62,35 @@ clear_to_initial() {
   _tics_since_birth = 0.0f;
 }
 
+////////////////////////////////////////////////////////////////////
+//    Function : soft_start
+//      Access : Public
+// Description : Causes system to use birth rate set by set_birth_rate()
+////////////////////////////////////////////////////////////////////
+
+INLINE void ParticleSystem::
+soft_start(float br) {
+  if (br > 0.0)
+    set_birth_rate(br);
+  _cur_birth_rate = _birth_rate;
+  _tics_since_birth = 0.0f;
+}
+
+////////////////////////////////////////////////////////////////////
+//    Function : soft_stop
+//      Access : Public
+// Description : Causes system to use birth rate set by 
+//               set_soft_birth_rate()
+////////////////////////////////////////////////////////////////////
+
+INLINE void ParticleSystem::
+soft_stop(float br) {
+  if (br > 0.0)
+    set_soft_birth_rate(br);
+  _cur_birth_rate = _soft_birth_rate;
+  _tics_since_birth = 0.0f;
+}
+
 ////             ///////////////////////////////////////////////////////
 //// SET METHODS ///////////////////////////////////////////////////////
 ////             ///////////////////////////////////////////////////////
@@ -84,9 +113,21 @@ set_pool_size(int size) {
 INLINE void ParticleSystem::
 set_birth_rate(float new_br) {
   _birth_rate = new_br;
+  _cur_birth_rate = _birth_rate;
   if(IS_NEARLY_ZERO(_birth_rate)) _birth_rate = NEARLY_ZERO(float);
 }
 
+////////////////////////////////////////////////////////////////////
+//    Function : set_soft_birth_rate
+//      Access : Public
+////////////////////////////////////////////////////////////////////
+
+INLINE void ParticleSystem::
+set_soft_birth_rate(float new_br) {
+  _soft_birth_rate = new_br;
+  if(IS_NEARLY_ZERO(_soft_birth_rate)) _soft_birth_rate = NEARLY_ZERO(float);
+}
+
 ////////////////////////////////////////////////////////////////////
 //    Function : set_litter_size
 //      Access : Public
@@ -294,6 +335,15 @@ get_birth_rate() const {
   return _birth_rate;
 }
 
+////////////////////////////////////////////////////////////////////
+//    Function : get_soft_birth_rate
+//      Access : Public
+////////////////////////////////////////////////////////////////////
+INLINE float ParticleSystem::
+get_soft_birth_rate() const {
+  return _soft_birth_rate;
+}
+
 ////////////////////////////////////////////////////////////////////
 //    Function : get_litter_size
 //      Access : Public

panda/src/particlesystem/particleSystem.cxx

@@ -46,7 +46,9 @@ ParticleSystem(int pool_size) :
   Physical(pool_size, false)
 {
   _birth_rate = 0.5f;
-  _tics_since_birth = _birth_rate;
+  _cur_birth_rate = _birth_rate;
+  _soft_birth_rate = HUGE_VAL;
+  _tics_since_birth = 0.0;
   _litter_size = 1;
   _litter_spread = 0;
   _living_particles = 0;
@@ -91,6 +93,7 @@ ParticleSystem(const ParticleSystem& copy) :
   _template_system_flag(false)
 {
   _birth_rate = copy._birth_rate;
+  _cur_birth_rate = copy._cur_birth_rate;
   _litter_size = copy._litter_size;
   _litter_spread = copy._litter_spread;
   _active_system_flag = copy._active_system_flag;
@@ -106,7 +109,7 @@ ParticleSystem(const ParticleSystem& copy) :
   _render_node = _renderer->get_render_node();
   _render_parent->add_child(_render_node);
 
-  _tics_since_birth = _birth_rate;
+  _tics_since_birth = 0.0;
   _system_lifespan = copy._system_lifespan;
   _living_particles = 0;
 
@@ -534,9 +537,9 @@ update(float dt) {
   // generate new particles if necessary.
   _tics_since_birth += dt;
 
-  while (_tics_since_birth >= _birth_rate) {
+  while (_tics_since_birth >= _cur_birth_rate) {
     birth_litter();
-    _tics_since_birth -= _birth_rate;
+    _tics_since_birth -= _cur_birth_rate;
   }
 
   #ifdef PARTICLE_SYSTEM_UPDATE_SENTRIES

panda/src/particlesystem/particleSystem.h

@@ -55,6 +55,7 @@ PUBLISHED:
   // access/queries
   INLINE void set_pool_size(int size);
   INLINE void set_birth_rate(float new_br);
+  INLINE void set_soft_birth_rate(float new_br);
   INLINE void set_litter_size(int new_ls);
   INLINE void set_litter_spread(int new_ls);
   INLINE void set_local_velocity_flag(bool lv);
@@ -75,6 +76,7 @@ PUBLISHED:
 
   INLINE int get_pool_size() const;
   INLINE float get_birth_rate() const;
+  INLINE float get_soft_birth_rate() const;
   INLINE int get_litter_size() const;
   INLINE int get_litter_spread() const;
   INLINE bool get_local_velocity_flag() const;
@@ -102,6 +104,8 @@ PUBLISHED:
   INLINE void render();
   INLINE void induce_labor();
   INLINE void clear_to_initial();
+  INLINE void soft_stop(float br = 0.0);
+  INLINE void soft_start(float br = 0.0);
   void update(float dt);
 
   virtual void output(ostream &out) const;
@@ -123,7 +127,9 @@ private:
 
   int _particle_pool_size;
   int _living_particles;
+  float _cur_birth_rate;
   float _birth_rate;
+  float _soft_birth_rate;
   float _tics_since_birth;
   int _litter_size;
   int _litter_spread;