Particles: give emitter its own state

High quality emitters need to maintain state themselves. For example,
this it needs to remember when it spawned the last particle.
This is especially important when the birth rate is changing over time.
Otherwise, there will be very visible artifacts.

It is quite likely that other components of the simulation need their own
state as well. Therefore, I refactored the `SimulationState` type a bit,
to make it more extensible. Instead of using hardcoded type numbers, a
string is used to identify the state type. Also, instead of having switch
statements in many places, there is a new `SimulationStateType` that
encapsulates information about how a specific state is created/freed/copied/...

I removed the integration with the point cache for now, because it was
not used anyway in it's current state.

13 files changed, 426 insertions, 300 deletions

diff --git a/source/blender/blenkernel/BKE_pointcache.h b/source/blender/blenkernel/BKE_pointcache.h
index a9abe2d0f6d..dc99ec7f56f 100644
--- a/source/blender/blenkernel/BKE_pointcache.h
+++ b/source/blender/blenkernel/BKE_pointcache.h
@@ -86,12 +86,10 @@ struct ListBase;
 struct Main;
 struct Object;
 struct ParticleKey;
-struct ParticleSimulationState;
 struct ParticleSystem;
 struct PointCache;
 struct RigidBodyWorld;
 struct Scene;
-struct Simulation;
 struct SoftBody;
 struct ViewLayer;
 
@@ -296,9 +294,6 @@ void BKE_ptcache_id_from_dynamicpaint(PTCacheID *pid,
                                       struct Object *ob,
                                       struct DynamicPaintSurface *surface);
 void BKE_ptcache_id_from_rigidbody(PTCacheID *pid, struct Object *ob, struct RigidBodyWorld *rbw);
-void BKE_ptcache_id_from_sim_particles(PTCacheID *pid,
-                                       struct ParticleSimulationState *state_orig,
-                                       struct ParticleSimulationState *state_cow);
 
 PTCacheID BKE_ptcache_id_find(struct Object *ob, struct Scene *scene, struct PointCache *cache);
 void BKE_ptcache_ids_from_object(struct ListBase *lb,
diff --git a/source/blender/blenkernel/BKE_simulation.h b/source/blender/blenkernel/BKE_simulation.h
index 36f4122f4dc..5aa71b6381d 100644
--- a/source/blender/blenkernel/BKE_simulation.h
+++ b/source/blender/blenkernel/BKE_simulation.h
@@ -34,13 +34,26 @@ void BKE_simulation_data_update(struct Depsgraph *depsgraph,
                                 struct Simulation *simulation);
 
 SimulationState *BKE_simulation_state_add(Simulation *simulation,
-                                          eSimulationStateType type,
+                                          const char *type,
                                           const char *name);
 void BKE_simulation_state_remove(Simulation *simulation, SimulationState *state);
 void BKE_simulation_state_remove_all(Simulation *simulation);
+void BKE_simulation_state_reset(Simulation *simulation, SimulationState *state);
+void BKE_simulation_state_reset_all(Simulation *simulation);
+SimulationState *BKE_simulation_state_try_find_by_name(Simulation *simulation, const char *name);
+SimulationState *BKE_simulation_state_try_find_by_name_and_type(Simulation *simulation,
+                                                                const char *name,
+                                                                const char *type);
+void BKE_simulation_state_copy_data(const SimulationState *src_state, SimulationState *dst_state);
 
 #ifdef __cplusplus
 }
 #endif
 
+#ifdef __cplusplus
+
+template<typename StateType> const char *BKE_simulation_get_state_type_name();
+
+#endif
+
 #endif /* __BKE_SIMULATION_H__ */
diff --git a/source/blender/blenkernel/intern/pointcache.c b/source/blender/blenkernel/intern/pointcache.c
index aa93c6cb854..4b09f7542c7 100644
--- a/source/blender/blenkernel/intern/pointcache.c
+++ b/source/blender/blenkernel/intern/pointcache.c
@@ -1885,81 +1885,6 @@ void BKE_ptcache_id_from_rigidbody(PTCacheID *pid, Object *ob, RigidBodyWorld *r
   pid->file_type = PTCACHE_FILE_PTCACHE;
 }
 
-static int ptcache_sim_particle_totpoint(void *state_v, int UNUSED(cfra))
-{
-  ParticleSimulationState *state = (ParticleSimulationState *)state_v;
-  return state->tot_particles;
-}
-
-static void ptcache_sim_particle_error(void *UNUSED(state_v), const char *UNUSED(message))
-{
-}
-
-static int ptcache_sim_particle_write(int index, void *state_v, void **data, int UNUSED(cfra))
-{
-  ParticleSimulationState *state = (ParticleSimulationState *)state_v;
-
-  const float *positions = (const float *)CustomData_get_layer_named(
-      &state->attributes, CD_PROP_FLOAT3, "Position");
-
-  PTCACHE_DATA_FROM(data, BPHYS_DATA_LOCATION, positions + (index * 3));
-
-  return 1;
-}
-static void ptcache_sim_particle_read(
-    int index, void *state_v, void **data, float UNUSED(cfra), const float *UNUSED(old_data))
-{
-  ParticleSimulationState *state = (ParticleSimulationState *)state_v;
-
-  BLI_assert(index < state->tot_particles);
-  float *positions = (float *)CustomData_get_layer_named(
-      &state->attributes, CD_PROP_FLOAT3, "Position");
-
-  PTCACHE_DATA_TO(data, BPHYS_DATA_LOCATION, 0, positions + (index * 3));
-}
-
-void BKE_ptcache_id_from_sim_particles(PTCacheID *pid,
-                                       ParticleSimulationState *state_orig,
-                                       ParticleSimulationState *state_cow)
-{
-  memset(pid, 0, sizeof(PTCacheID));
-
-  pid->calldata = state_cow;
-  pid->type = PTCACHE_TYPE_SIM_PARTICLES;
-  pid->cache = state_orig->point_cache;
-  pid->cache_ptr = &state_orig->point_cache;
-  pid->ptcaches = &state_orig->ptcaches;
-  pid->totpoint = ptcache_sim_particle_totpoint;
-  pid->totwrite = ptcache_sim_particle_totpoint;
-  pid->error = ptcache_sim_particle_error;
-
-  pid->write_point = ptcache_sim_particle_write;
-  pid->read_point = ptcache_sim_particle_read;
-  pid->interpolate_point = NULL;
-
-  pid->write_stream = NULL;
-  pid->read_stream = NULL;
-
-  pid->write_openvdb_stream = NULL;
-  pid->read_openvdb_stream = NULL;
-
-  pid->write_extra_data = NULL;
-  pid->read_extra_data = NULL;
-  pid->interpolate_extra_data = NULL;
-
-  pid->write_header = NULL;
-  pid->read_header = NULL;
-
-  pid->data_types = 1 << BPHYS_DATA_LOCATION;
-  pid->info_types = 0;
-
-  pid->stack_index = 0;
-
-  pid->default_step = 1;
-  pid->max_step = 1;
-  pid->file_type = PTCACHE_FILE_PTCACHE;
-}
-
 /**
  * \param ob: Optional, may be NULL.
  * \param scene: Optional may be NULL.
@@ -2059,17 +1984,7 @@ static bool foreach_object_modifier_ptcache(Object *object,
       }
     }
     else if (md->type == eModifierType_Simulation) {
-      SimulationModifierData *smd = (SimulationModifierData *)md;
-      if (smd->simulation) {
-        LISTBASE_FOREACH (SimulationState *, state, &smd->simulation->states) {
-          switch ((eSimulationStateType)state->type) {
-            case SIM_STATE_TYPE_PARTICLES: {
-              /* TODO(jacques) */
-              break;
-            }
-          }
-        }
-      }
+      /* TODO(jacques) */
     }
   }
   return true;
diff --git a/source/blender/blenkernel/intern/simulation.cc b/source/blender/blenkernel/intern/simulation.cc
index 1f11869e21c..95340e4e29c 100644
--- a/source/blender/blenkernel/intern/simulation.cc
+++ b/source/blender/blenkernel/intern/simulation.cc
@@ -51,6 +51,7 @@
 #include "NOD_node_tree_multi_function.hh"
 #include "NOD_simulation.h"
 
+#include "BLI_map.hh"
 #include "BLT_translation.h"
 
 #include "FN_attributes_ref.hh"
@@ -62,6 +63,22 @@
 
 #include "SIM_simulation_update.hh"
 
+using StateInitFunction = void (*)(SimulationState *state);
+using StateResetFunction = void (*)(SimulationState *state);
+using StateRemoveFunction = void (*)(SimulationState *state);
+using StateCopyFunction = void (*)(const SimulationState *src, SimulationState *dst);
+
+struct SimulationStateType {
+  const char *name;
+  int size;
+  StateInitFunction init;
+  StateResetFunction reset;
+  StateRemoveFunction remove;
+  StateCopyFunction copy;
+};
+
+static const SimulationStateType *try_get_state_type(blender::StringRefNull type_name);
+
 static void simulation_init_data(ID *id)
 {
   Simulation *simulation = (Simulation *)id;
@@ -76,7 +93,7 @@ static void simulation_init_data(ID *id)
 static void simulation_copy_data(Main *bmain, ID *id_dst, const ID *id_src, const int flag)
 {
   Simulation *simulation_dst = (Simulation *)id_dst;
-  Simulation *simulation_src = (Simulation *)id_src;
+  const Simulation *simulation_src = (const Simulation *)id_src;
 
   /* We always need allocation of our private ID data. */
   const int flag_private_id_data = flag & ~LIB_ID_CREATE_NO_ALLOCATE;
@@ -89,76 +106,16 @@ static void simulation_copy_data(Main *bmain, ID *id_dst, const ID *id_src, cons
   }
 
   BLI_listbase_clear(&simulation_dst->states);
+  LISTBASE_FOREACH (const SimulationState *, state_src, &simulation_src->states) {
+    SimulationState *state_dst = BKE_simulation_state_add(
+        simulation_dst, state_src->type, state_src->name);
+    BKE_simulation_state_copy_data(state_src, state_dst);
+  }
 
   BLI_duplicatelist(&simulation_dst->persistent_data_handles,
                     &simulation_src->persistent_data_handles);
 }
 
-static void free_simulation_state_head(SimulationState *state)
-{
-  MEM_freeN(state->name);
-}
-
-static void free_particle_simulation_state(ParticleSimulationState *state)
-{
-  free_simulation_state_head(&state->head);
-  CustomData_free(&state->attributes, state->tot_particles);
-  BKE_ptcache_free_list(&state->ptcaches);
-  MEM_freeN(state);
-}
-
-SimulationState *BKE_simulation_state_add(Simulation *simulation,
-                                          eSimulationStateType type,
-                                          const char *name)
-{
-  BLI_assert(simulation != nullptr);
-  BLI_assert(name != nullptr);
-
-  bool is_cow_simulation = DEG_is_evaluated_id(&simulation->id);
-
-  switch (type) {
-    case SIM_STATE_TYPE_PARTICLES: {
-      ParticleSimulationState *state = (ParticleSimulationState *)MEM_callocN(sizeof(*state), AT);
-      state->head.type = SIM_STATE_TYPE_PARTICLES;
-      state->head.name = BLI_strdup(name);
-      CustomData_reset(&state->attributes);
-
-      if (!is_cow_simulation) {
-        state->point_cache = BKE_ptcache_add(&state->ptcaches);
-      }
-
-      BLI_addtail(&simulation->states, state);
-      return &state->head;
-    }
-  }
-
-  BLI_assert(false);
-  return nullptr;
-}
-
-void BKE_simulation_state_remove(Simulation *simulation, SimulationState *state)
-{
-  BLI_assert(simulation != nullptr);
-  BLI_assert(state != nullptr);
-  BLI_assert(BLI_findindex(&simulation->states, state) >= 0);
-
-  BLI_remlink(&simulation->states, state);
-  switch ((eSimulationStateType)state->type) {
-    case SIM_STATE_TYPE_PARTICLES: {
-      free_particle_simulation_state((ParticleSimulationState *)state);
-      break;
-    }
-  }
-}
-
-void BKE_simulation_state_remove_all(Simulation *simulation)
-{
-  BLI_assert(simulation != nullptr);
-  while (!BLI_listbase_is_empty(&simulation->states)) {
-    BKE_simulation_state_remove(simulation, (SimulationState *)simulation->states.first);
-  }
-}
-
 static void simulation_free_data(ID *id)
 {
   Simulation *simulation = (Simulation *)id;
@@ -215,7 +172,195 @@ void *BKE_simulation_add(Main *bmain, const char *name)
   return simulation;
 }
 
+SimulationState *BKE_simulation_state_add(Simulation *simulation,
+                                          const char *type,
+                                          const char *name)
+{
+  BLI_assert(simulation != nullptr);
+  BLI_assert(name != nullptr);
+
+  const SimulationStateType *state_type = try_get_state_type(type);
+  BLI_assert(state_type != nullptr);
+
+  SimulationState *state = (SimulationState *)MEM_callocN(state_type->size, AT);
+  state->type = BLI_strdup(type);
+  state->name = BLI_strdup(name);
+
+  state_type->init(state);
+  BLI_addtail(&simulation->states, state);
+  return state;
+}
+
+void BKE_simulation_state_remove(Simulation *simulation, SimulationState *state)
+{
+  BLI_assert(simulation != nullptr);
+  BLI_assert(state != nullptr);
+  BLI_assert(BLI_findindex(&simulation->states, state) >= 0);
+
+  BLI_remlink(&simulation->states, state);
+  const SimulationStateType *state_type = try_get_state_type(state->type);
+  BLI_assert(state_type != nullptr);
+  state_type->remove(state);
+  MEM_freeN(state->name);
+  MEM_freeN(state->type);
+  MEM_freeN(state);
+}
+
+void BKE_simulation_state_remove_all(Simulation *simulation)
+{
+  BLI_assert(simulation != nullptr);
+
+  while (!BLI_listbase_is_empty(&simulation->states)) {
+    BKE_simulation_state_remove(simulation, (SimulationState *)simulation->states.first);
+  }
+}
+
+void BKE_simulation_state_reset(Simulation *UNUSED(simulation), SimulationState *state)
+{
+  BLI_assert(state != nullptr);
+
+  const SimulationStateType *state_type = try_get_state_type(state->type);
+  BLI_assert(state_type != nullptr);
+  state_type->reset(state);
+}
+
+void BKE_simulation_state_reset_all(Simulation *simulation)
+{
+  BLI_assert(simulation != nullptr);
+
+  LISTBASE_FOREACH (SimulationState *, state, &simulation->states) {
+    BKE_simulation_state_reset(simulation, state);
+  }
+}
+
+void BKE_simulation_state_copy_data(const SimulationState *src_state, SimulationState *dst_state)
+{
+  BLI_assert(src_state != nullptr);
+  BLI_assert(dst_state != nullptr);
+  BLI_assert(STREQ(src_state->type, dst_state->type));
+
+  const SimulationStateType *state_type = try_get_state_type(src_state->type);
+  BLI_assert(state_type != nullptr);
+  state_type->copy(src_state, dst_state);
+}
+
+SimulationState *BKE_simulation_state_try_find_by_name(Simulation *simulation, const char *name)
+{
+  if (simulation == nullptr) {
+    return nullptr;
+  }
+  if (name == nullptr) {
+    return nullptr;
+  }
+
+  LISTBASE_FOREACH (SimulationState *, state, &simulation->states) {
+    if (STREQ(state->name, name)) {
+      return state;
+    }
+  }
+  return nullptr;
+}
+
+SimulationState *BKE_simulation_state_try_find_by_name_and_type(Simulation *simulation,
+                                                                const char *name,
+                                                                const char *type)
+{
+  if (type == nullptr) {
+    return nullptr;
+  }
+
+  SimulationState *state = BKE_simulation_state_try_find_by_name(simulation, name);
+  if (state == nullptr) {
+    return nullptr;
+  }
+  if (STREQ(state->type, type)) {
+    return state;
+  }
+  return nullptr;
+}
+
 void BKE_simulation_data_update(Depsgraph *depsgraph, Scene *scene, Simulation *simulation)
 {
   blender::sim::update_simulation_in_depsgraph(depsgraph, scene, simulation);
 }
+
+using StateTypeMap = blender::Map<std::string, std::unique_ptr<SimulationStateType>>;
+
+template<typename T>
+static void add_state_type(StateTypeMap &map,
+                           const char *name,
+                           void (*init)(T *state),
+                           void (*reset)(T *state),
+                           void (*remove)(T *state),
+                           void (*copy)(const T *src, T *dst))
+{
+  SimulationStateType state_type{
+      name,
+      (int)sizeof(T),
+      (StateInitFunction)init,
+      (StateResetFunction)reset,
+      (StateRemoveFunction)remove,
+      (StateCopyFunction)copy,
+  };
+  map.add_new(name, std::make_unique<SimulationStateType>(state_type));
+}
+
+static StateTypeMap init_state_types()
+{
+  StateTypeMap map;
+  add_state_type<ParticleSimulationState>(
+      map,
+      SIM_TYPE_NAME_PARTICLE_SIMULATION,
+      [](ParticleSimulationState *state) { CustomData_reset(&state->attributes); },
+      [](ParticleSimulationState *state) {
+        CustomData_free(&state->attributes, state->tot_particles);
+        state->tot_particles = 0;
+        state->next_particle_id = 0;
+      },
+      [](ParticleSimulationState *state) {
+        CustomData_free(&state->attributes, state->tot_particles);
+      },
+      [](const ParticleSimulationState *src, ParticleSimulationState *dst) {
+        CustomData_free(&dst->attributes, dst->tot_particles);
+        dst->tot_particles = src->tot_particles;
+        dst->next_particle_id = src->next_particle_id;
+        CustomData_copy(
+            &src->attributes, &dst->attributes, CD_MASK_ALL, CD_DUPLICATE, src->tot_particles);
+      });
+
+  add_state_type<ParticleMeshEmitterSimulationState>(
+      map,
+      SIM_TYPE_NAME_PARTICLE_MESH_EMITTER,
+      [](ParticleMeshEmitterSimulationState *UNUSED(state)) {},
+      [](ParticleMeshEmitterSimulationState *state) { state->last_birth_time = 0.0f; },
+      [](ParticleMeshEmitterSimulationState *UNUSED(state)) {},
+      [](const ParticleMeshEmitterSimulationState *src, ParticleMeshEmitterSimulationState *dst) {
+        dst->last_birth_time = src->last_birth_time;
+      });
+  return map;
+}
+
+static StateTypeMap &get_state_types()
+{
+  static StateTypeMap state_type_map = init_state_types();
+  return state_type_map;
+}
+
+static const SimulationStateType *try_get_state_type(blender::StringRefNull type_name)
+{
+  std::unique_ptr<SimulationStateType> *type = get_state_types().lookup_ptr_as(type_name);
+  if (type == nullptr) {
+    return nullptr;
+  }
+  return type->get();
+}
+
+template<> const char *BKE_simulation_get_state_type_name<ParticleSimulationState>()
+{
+  return SIM_TYPE_NAME_PARTICLE_SIMULATION;
+}
+
+template<> const char *BKE_simulation_get_state_type_name<ParticleMeshEmitterSimulationState>()
+{
+  return SIM_TYPE_NAME_PARTICLE_MESH_EMITTER;
+}
diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index f443859e62c..9320187f2a0 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -8691,14 +8691,10 @@ static void direct_link_simulation(BlendDataReader *reader, Simulation *simulati
   BLO_read_list(reader, &simulation->states);
   LISTBASE_FOREACH (SimulationState *, state, &simulation->states) {
     BLO_read_data_address(reader, &state->name);
-    switch ((eSimulationStateType)state->type) {
-      case SIM_STATE_TYPE_PARTICLES: {
-        ParticleSimulationState *particle_state = (ParticleSimulationState *)state;
-        direct_link_customdata(reader, &particle_state->attributes, particle_state->tot_particles);
-        direct_link_pointcache_list(
-            reader, &particle_state->ptcaches, &particle_state->point_cache, 0);
-        break;
-      };
+    BLO_read_data_address(reader, &state->type);
+    if (STREQ(state->type, SIM_TYPE_NAME_PARTICLE_SIMULATION)) {
+      ParticleSimulationState *particle_state = (ParticleSimulationState *)state;
+      direct_link_customdata(reader, &particle_state->attributes, particle_state->tot_particles);
     }
   }
 
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index d33d8032ed1..46ac6b43c92 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -3833,31 +3833,33 @@ static void write_simulation(BlendWriter *writer, Simulation *simulation, const
 
     LISTBASE_FOREACH (SimulationState *, state, &simulation->states) {
       BLO_write_string(writer, state->name);
-      switch ((eSimulationStateType)state->type) {
-        case SIM_STATE_TYPE_PARTICLES: {
-          ParticleSimulationState *particle_state = (ParticleSimulationState *)state;
-          BLO_write_struct(writer, ParticleSimulationState, particle_state);
-
-          CustomDataLayer *layers = NULL;
-          CustomDataLayer layers_buff[CD_TEMP_CHUNK_SIZE];
-          CustomData_file_write_prepare(
-              &particle_state->attributes, &layers, layers_buff, ARRAY_SIZE(layers_buff));
-
-          write_customdata(writer,
-                           &simulation->id,
-                           particle_state->tot_particles,
-                           &particle_state->attributes,
-                           layers,
-                           CD_MASK_ALL);
-
-          if (layers != NULL && layers != layers_buff) {
-            MEM_freeN(layers);
-          }
-
-          write_pointcaches(writer, &particle_state->ptcaches);
-          break;
+      BLO_write_string(writer, state->type);
+      /* TODO: Decentralize this part. */
+      if (STREQ(state->type, SIM_TYPE_NAME_PARTICLE_SIMULATION)) {
+        ParticleSimulationState *particle_state = (ParticleSimulationState *)state;
+        BLO_write_struct(writer, ParticleSimulationState, particle_state);
+
+        CustomDataLayer *layers = NULL;
+        CustomDataLayer layers_buff[CD_TEMP_CHUNK_SIZE];
+        CustomData_file_write_prepare(
+            &particle_state->attributes, &layers, layers_buff, ARRAY_SIZE(layers_buff));
+
+        write_customdata(writer,
+                         &simulation->id,
+                         particle_state->tot_particles,
+                         &particle_state->attributes,
+                         layers,
+                         CD_MASK_ALL);
+
+        if (layers != NULL && layers != layers_buff) {
+          MEM_freeN(layers);
         }
       }
+      else if (STREQ(state->type, SIM_TYPE_NAME_PARTICLE_MESH_EMITTER)) {
+        ParticleMeshEmitterSimulationState *emitter_state = (ParticleMeshEmitterSimulationState *)
+            state;
+        BLO_write_struct(writer, ParticleMeshEmitterSimulationState, emitter_state);
+      }
     }
 
     BLO_write_struct_list(writer, PersistentDataHandleItem, &simulation->persistent_data_handles);
diff --git a/source/blender/makesdna/DNA_simulation_types.h b/source/blender/makesdna/DNA_simulation_types.h
index f7a7f94da53..5bb0e50e089 100644
--- a/source/blender/makesdna/DNA_simulation_types.h
+++ b/source/blender/makesdna/DNA_simulation_types.h
@@ -46,10 +46,7 @@ typedef struct SimulationState {
   struct SimulationState *next;
   struct SimulationState *prev;
 
-  /** eSimulationStateType */
-  int type;
-  int _pad;
-
+  char *type;
   char *name;
 } SimulationState;
 
@@ -60,13 +57,15 @@ typedef struct ParticleSimulationState {
   int tot_particles;
   int next_particle_id;
   struct CustomData attributes;
-
-  /** Caches the state of the particles over time. The cache only exists on the original data
-   * block, not on cow copies. */
-  struct PointCache *point_cache;
-  struct ListBase ptcaches;
 } ParticleSimulationState;
 
+typedef struct ParticleMeshEmitterSimulationState {
+  SimulationState head;
+
+  float last_birth_time;
+  char _pad[4];
+} ParticleMeshEmitterSimulationState;
+
 /** Stores a mapping between an integer handle and a corresponding ID data block. */
 typedef struct PersistentDataHandleItem {
   struct PersistentDataHandleItem *next;
@@ -81,9 +80,7 @@ enum {
   SIM_DS_EXPAND = (1 << 0),
 };
 
-/* SimulationCache.type */
-typedef enum eSimulationStateType {
-  SIM_STATE_TYPE_PARTICLES = 0,
-} eSimulationStateType;
+#define SIM_TYPE_NAME_PARTICLE_SIMULATION "Particle Simulation"
+#define SIM_TYPE_NAME_PARTICLE_MESH_EMITTER "Particle Mesh Emitter"
 
 #endif /* __DNA_SIMULATION_TYPES_H__ */
diff --git a/source/blender/modifiers/intern/MOD_simulation.cc b/source/blender/modifiers/intern/MOD_simulation.cc
index 819ed320255..d9cc9840e08 100644
--- a/source/blender/modifiers/intern/MOD_simulation.cc
+++ b/source/blender/modifiers/intern/MOD_simulation.cc
@@ -93,20 +93,8 @@ static bool isDisabled(const struct Scene *UNUSED(scene),
 
 static const ParticleSimulationState *find_particle_state(SimulationModifierData *smd)
 {
-  if (smd->simulation == nullptr) {
-    return nullptr;
-  }
-  if (smd->data_path == nullptr) {
-    return nullptr;
-  }
-  LISTBASE_FOREACH (const SimulationState *, state, &smd->simulation->states) {
-    if (STREQ(smd->data_path, state->name)) {
-      if (state->type == SIM_STATE_TYPE_PARTICLES) {
-        return (ParticleSimulationState *)state;
-      }
-    }
-  }
-  return nullptr;
+  return (const ParticleSimulationState *)BKE_simulation_state_try_find_by_name_and_type(
+      smd->simulation, smd->data_path, SIM_TYPE_NAME_PARTICLE_SIMULATION);
 }
 
 static PointCloud *modifyPointCloud(ModifierData *md,
diff --git a/source/blender/simulation/intern/simulation_collect_influences.cc b/source/blender/simulation/intern/simulation_collect_influences.cc
index 4760063daca..764e587d157 100644
--- a/source/blender/simulation/intern/simulation_collect_influences.cc
+++ b/source/blender/simulation/intern/simulation_collect_influences.cc
@@ -280,17 +280,30 @@ static void collect_forces(nodes::MFNetworkTreeMap &network_map,
 class MyBasicEmitter : public ParticleEmitter {
  private:
   Array<std::string> names_;
+  std::string my_state_;
   const fn::MultiFunction &inputs_fn_;
   uint32_t seed_;
 
  public:
-  MyBasicEmitter(Array<std::string> names, const fn::MultiFunction &inputs_fn, uint32_t seed)
-      : names_(std::move(names)), inputs_fn_(inputs_fn), seed_(seed)
+  MyBasicEmitter(Array<std::string> names,
+                 std::string my_state,
+                 const fn::MultiFunction &inputs_fn,
+                 uint32_t seed)
+      : names_(std::move(names)),
+        my_state_(std::move(my_state)),
+        inputs_fn_(inputs_fn),
+        seed_(seed)
   {
   }
 
   void emit(ParticleEmitterContext &context) const override
   {
+    auto *state = context.solve_context().state_map().lookup<ParticleMeshEmitterSimulationState>(
+        my_state_);
+    if (state == nullptr) {
+      return;
+    }
+
     fn::MFContextBuilder mf_context;
     mf_context.add_global_context("PersistentDataHandleMap",
                                   &context.solve_context().handle_map());
@@ -311,15 +324,17 @@ class MyBasicEmitter : public ParticleEmitter {
     Vector<float3> new_velocities;
     Vector<float> new_birth_times;
 
-    float start_time = context.simulation_time_interval().start();
+    TimeInterval time_interval = context.simulation_time_interval();
+    float start_time = time_interval.start();
     RandomNumberGenerator rng{(*(uint32_t *)&start_time) ^ seed_};
 
-    int amount = rate * 10;
-    for (int i : IndexRange(amount)) {
-      UNUSED_VARS(i);
+    const float time_between_particles = 1.0f / rate;
+    while (state->last_birth_time + time_between_particles < time_interval.end()) {
       new_positions.append(rng.get_unit_float3() * 0.3 + float3(object->loc));
       new_velocities.append(rng.get_unit_float3());
-      new_birth_times.append(context.simulation_time_interval().start());
+      const float birth_time = state->last_birth_time + time_between_particles;
+      new_birth_times.append(birth_time);
+      state->last_birth_time = birth_time;
     }
 
     for (StringRef name : names_) {
@@ -328,6 +343,7 @@ class MyBasicEmitter : public ParticleEmitter {
         return;
       }
 
+      int amount = new_positions.size();
       fn::MutableAttributesRef attributes = allocator->allocate(amount);
 
       initialized_copy_n(new_positions.data(), amount, attributes.get<float3>("Position").data());
@@ -352,7 +368,8 @@ static Vector<const nodes::DNode *> find_linked_particle_simulations(
 
 static ParticleEmitter *create_particle_emitter(const nodes::DNode &dnode,
                                                 ResourceCollector &resources,
-                                                nodes::MFNetworkTreeMap &network_map)
+                                                nodes::MFNetworkTreeMap &network_map,
+                                                RequiredStates &r_required_states)
 {
   Vector<const nodes::DNode *> simulation_dnodes = find_linked_particle_simulations(
       dnode.output(0));
@@ -377,19 +394,23 @@ static ParticleEmitter *create_particle_emitter(const nodes::DNode &dnode,
   fn::MultiFunction &inputs_fn = resources.construct<fn::MFNetworkEvaluator>(
       AT, Span<const fn::MFOutputSocket *>(), input_sockets.as_span());
 
-  uint32_t seed = DefaultHash<std::string>{}(dnode_to_path(dnode));
+  std::string my_state_name = dnode_to_path(dnode);
+  r_required_states.add(my_state_name, SIM_TYPE_NAME_PARTICLE_MESH_EMITTER);
+  uint32_t seed = DefaultHash<std::string>{}(my_state_name);
   ParticleEmitter &emitter = resources.construct<MyBasicEmitter>(
-      AT, std::move(names), inputs_fn, seed);
+      AT, std::move(names), std::move(my_state_name), inputs_fn, seed);
   return &emitter;
 }
 
 static void collect_emitters(nodes::MFNetworkTreeMap &network_map,
                              ResourceCollector &resources,
-                             SimulationInfluences &r_influences)
+                             SimulationInfluences &r_influences,
+                             RequiredStates &r_required_states)
 {
   for (const nodes::DNode *dnode :
        network_map.tree().nodes_by_type("SimulationNodeParticleMeshEmitter")) {
-    ParticleEmitter *emitter = create_particle_emitter(*dnode, resources, network_map);
+    ParticleEmitter *emitter = create_particle_emitter(
+        *dnode, resources, network_map, r_required_states);
     if (emitter != nullptr) {
       r_influences.particle_emitters.append(emitter);
     }
@@ -433,7 +454,7 @@ static void find_used_data_blocks(const nodes::DerivedNodeTree &tree,
 void collect_simulation_influences(Simulation &simulation,
                                    ResourceCollector &resources,
                                    SimulationInfluences &r_influences,
-                                   SimulationStatesInfo &r_states_info)
+                                   RequiredStates &r_required_states)
 {
   nodes::NodeTreeRefMap tree_refs;
   const nodes::DerivedNodeTree tree{simulation.nodetree, tree_refs};
@@ -452,10 +473,10 @@ void collect_simulation_influences(Simulation &simulation,
   // WM_clipboard_text_set(network.to_dot().c_str(), false);
 
   collect_forces(network_map, resources, data_sources, r_influences);
-  collect_emitters(network_map, resources, r_influences);
+  collect_emitters(network_map, resources, r_influences, r_required_states);
 
   for (const nodes::DNode *dnode : get_particle_simulation_nodes(tree)) {
-    r_states_info.particle_simulation_names.add(dnode_to_path(*dnode));
+    r_required_states.add(dnode_to_path(*dnode), SIM_TYPE_NAME_PARTICLE_SIMULATION);
   }
 
   find_used_data_blocks(tree, r_influences);
diff --git a/source/blender/simulation/intern/simulation_collect_influences.hh b/source/blender/simulation/intern/simulation_collect_influences.hh
index cca396ffa66..42cbea6977e 100644
--- a/source/blender/simulation/intern/simulation_collect_influences.hh
+++ b/source/blender/simulation/intern/simulation_collect_influences.hh
@@ -25,14 +25,43 @@
 
 namespace blender::sim {
 
-struct SimulationStatesInfo {
-  VectorSet<std::string> particle_simulation_names;
+class RequiredStates {
+ private:
+  Map<std::string, const char *> state_type_by_state_name_;
+
+ public:
+  void add(std::string state_name, const char *state_type)
+  {
+    BLI_assert(state_type != nullptr);
+    const char *type_name = state_type_by_state_name_.lookup_default(state_name, nullptr);
+    if (type_name != nullptr) {
+      if (!STREQ(state_type, type_name)) {
+        std::cout << "Warning: Tried to have two different states with the same name.\n";
+        std::cout << "    Name: " << state_name << "\n";
+        std::cout << "    Type 1: " << state_type << "\n";
+        std::cout << "    Type 2: " << type_name << "\n";
+      }
+      return;
+    }
+
+    state_type_by_state_name_.add(std::move(state_name), state_type);
+  }
+
+  const Map<std::string, const char *> &states() const
+  {
+    return state_type_by_state_name_;
+  }
+
+  bool is_required(StringRef state_name, StringRef state_type) const
+  {
+    return state_type_by_state_name_.lookup_default_as(state_name, "") == state_type;
+  }
 };
 
 void collect_simulation_influences(Simulation &simulation,
                                    ResourceCollector &resources,
                                    SimulationInfluences &r_influences,
-                                   SimulationStatesInfo &r_states_info);
+                                   RequiredStates &r_required_states);
 
 }  // namespace blender::sim
 
diff --git a/source/blender/simulation/intern/simulation_solver.cc b/source/blender/simulation/intern/simulation_solver.cc
index 158c50957df..ee7a8d40035 100644
--- a/source/blender/simulation/intern/simulation_solver.cc
+++ b/source/blender/simulation/intern/simulation_solver.cc
@@ -312,20 +312,21 @@ void solve_simulation_time_step(Simulation &simulation,
     handle_map.add(handle->handle, *handle->id);
   }
 
+  SimulationStateMap state_map;
+  LISTBASE_FOREACH (SimulationState *, state, &simulation.states) {
+    state_map.add(state);
+  }
+
   SimulationSolveContext solve_context{simulation,
                                        depsgraph,
                                        influences,
                                        TimeInterval(simulation.current_simulation_time, time_step),
+                                       state_map,
                                        handle_map};
   TimeInterval simulation_time_interval{simulation.current_simulation_time, time_step};
 
-  Vector<SimulationState *> simulation_states{simulation.states};
-  Vector<ParticleSimulationState *> particle_simulation_states;
-  for (SimulationState *state : simulation_states) {
-    if (state->type == SIM_STATE_TYPE_PARTICLES) {
-      particle_simulation_states.append((ParticleSimulationState *)state);
-    }
-  }
+  Span<ParticleSimulationState *> particle_simulation_states =
+      state_map.lookup<ParticleSimulationState>();
 
   Map<std::string, std::unique_ptr<fn::AttributesInfo>> attribute_infos;
   Map<std::string, std::unique_ptr<ParticleAllocator>> particle_allocators_map;
diff --git a/source/blender/simulation/intern/simulation_solver.hh b/source/blender/simulation/intern/simulation_solver.hh
index 1d1b9935661..2dc0921ad9e 100644
--- a/source/blender/simulation/intern/simulation_solver.hh
+++ b/source/blender/simulation/intern/simulation_solver.hh
@@ -25,6 +25,7 @@
 #include "FN_attributes_ref.hh"
 
 #include "BKE_persistent_data_handle.hh"
+#include "BKE_simulation.h"
 
 #include "particle_allocator.hh"
 #include "time_interval.hh"
@@ -55,12 +56,61 @@ struct SimulationInfluences {
   VectorSet<ID *> used_data_blocks;
 };
 
+class SimulationStateMap {
+ private:
+  Map<StringRefNull, SimulationState *> states_by_name_;
+  Map<StringRefNull, Vector<SimulationState *>> states_by_type_;
+
+ public:
+  void add(SimulationState *state)
+  {
+    states_by_name_.add_new(state->name, state);
+    states_by_type_.lookup_or_add_default(state->type).append(state);
+  }
+
+  template<typename StateType> StateType *lookup(StringRef name) const
+  {
+    const char *type = BKE_simulation_get_state_type_name<StateType>();
+    return (StateType *)this->lookup_name_type(name, type);
+  }
+
+  template<typename StateType> Span<StateType *> lookup() const
+  {
+    const char *type = BKE_simulation_get_state_type_name<StateType>();
+    return this->lookup_type(type).cast<StateType *>();
+  }
+
+  SimulationState *lookup_name_type(StringRef name, StringRef type) const
+  {
+    SimulationState *state = states_by_name_.lookup_default_as(name, nullptr);
+    if (state == nullptr) {
+      return nullptr;
+    }
+    if (state->type == type) {
+      return state;
+    }
+    return nullptr;
+  }
+
+  Span<SimulationState *> lookup_type(StringRef type) const
+  {
+    const Vector<SimulationState *> *states = states_by_type_.lookup_ptr_as(type);
+    if (states == nullptr) {
+      return {};
+    }
+    else {
+      return states->as_span();
+    }
+  }
+};
+
 class SimulationSolveContext {
  private:
   Simulation &simulation_;
   Depsgraph &depsgraph_;
   const SimulationInfluences &influences_;
   TimeInterval solve_interval_;
+  const SimulationStateMap &state_map_;
   const bke::PersistentDataHandleMap &id_handle_map_;
 
  public:
@@ -68,11 +118,13 @@ class SimulationSolveContext {
                          Depsgraph &depsgraph,
                          const SimulationInfluences &influences,
                          TimeInterval solve_interval,
+                         const SimulationStateMap &state_map,
                          const bke::PersistentDataHandleMap &handle_map)
       : simulation_(simulation),
         depsgraph_(depsgraph),
         influences_(influences),
         solve_interval_(solve_interval),
+        state_map_(state_map),
         id_handle_map_(handle_map)
   {
   }
@@ -91,6 +143,11 @@ class SimulationSolveContext {
   {
     return id_handle_map_;
   }
+
+  const SimulationStateMap &state_map() const
+  {
+    return state_map_;
+  }
 };
 
 class ParticleAllocators {
diff --git a/source/blender/simulation/intern/simulation_update.cc b/source/blender/simulation/intern/simulation_update.cc
index 5328304863b..09219e0238f 100644
--- a/source/blender/simulation/intern/simulation_update.cc
+++ b/source/blender/simulation/intern/simulation_update.cc
@@ -37,88 +37,55 @@
 
 namespace blender::sim {
 
-static void copy_states_to_cow(Simulation *simulation_orig, Simulation *simulation_cow)
+static void copy_states_to_cow(const Simulation *simulation_orig, Simulation *simulation_cow)
 {
   BKE_simulation_state_remove_all(simulation_cow);
   simulation_cow->current_frame = simulation_orig->current_frame;
 
-  LISTBASE_FOREACH (SimulationState *, state_orig, &simulation_orig->states) {
-    switch ((eSimulationStateType)state_orig->type) {
-      case SIM_STATE_TYPE_PARTICLES: {
-        ParticleSimulationState *particle_state_orig = (ParticleSimulationState *)state_orig;
-        ParticleSimulationState *particle_state_cow = (ParticleSimulationState *)
-            BKE_simulation_state_add(simulation_cow, SIM_STATE_TYPE_PARTICLES, state_orig->name);
-        particle_state_cow->tot_particles = particle_state_orig->tot_particles;
-        CustomData_copy(&particle_state_orig->attributes,
-                        &particle_state_cow->attributes,
-                        CD_MASK_ALL,
-                        CD_DUPLICATE,
-                        particle_state_orig->tot_particles);
-        break;
-      }
-    }
+  LISTBASE_FOREACH (const SimulationState *, state_orig, &simulation_orig->states) {
+    SimulationState *state_cow = BKE_simulation_state_add(
+        simulation_cow, state_orig->type, state_orig->name);
+    BKE_simulation_state_copy_data(state_orig, state_cow);
   }
 }
 
-static void remove_unused_states(Simulation *simulation, const VectorSet<std::string> &state_names)
+static void remove_unused_states(Simulation *simulation, const RequiredStates &required_states)
 {
   LISTBASE_FOREACH_MUTABLE (SimulationState *, state, &simulation->states) {
-    if (!state_names.contains(state->name)) {
+    if (!required_states.is_required(state->name, state->type)) {
       BKE_simulation_state_remove(simulation, state);
     }
   }
 }
 
-static void reset_states(Simulation *simulation)
+static void add_missing_states(Simulation *simulation, const RequiredStates &required_states)
 {
-  LISTBASE_FOREACH (SimulationState *, state, &simulation->states) {
-    switch ((eSimulationStateType)state->type) {
-      case SIM_STATE_TYPE_PARTICLES: {
-        ParticleSimulationState *particle_state = (ParticleSimulationState *)state;
-        CustomData_free(&particle_state->attributes, particle_state->tot_particles);
-        particle_state->tot_particles = 0;
-        break;
-      }
-    }
-  }
-}
+  for (auto &&item : required_states.states().items()) {
+    const char *name = item.key.c_str();
+    const char *type = item.value;
 
-static SimulationState *try_find_state_by_name(Simulation *simulation, StringRef name)
-{
-  LISTBASE_FOREACH (SimulationState *, state, &simulation->states) {
-    if (state->name == name) {
-      return state;
-    }
-  }
-  return nullptr;
-}
+    SimulationState *state = BKE_simulation_state_try_find_by_name_and_type(
+        simulation, name, type);
 
-static void add_missing_particle_states(Simulation *simulation, Span<std::string> state_names)
-{
-  for (StringRefNull name : state_names) {
-    SimulationState *state = try_find_state_by_name(simulation, name);
-    if (state != nullptr) {
-      BLI_assert(state->type == SIM_STATE_TYPE_PARTICLES);
-      continue;
+    if (state == nullptr) {
+      BKE_simulation_state_add(simulation, type, name);
     }
-
-    BKE_simulation_state_add(simulation, SIM_STATE_TYPE_PARTICLES, name.c_str());
   }
 }
 
 static void reinitialize_empty_simulation_states(Simulation *simulation,
-                                                 const SimulationStatesInfo &states_info)
+                                                 const RequiredStates &required_states)
 {
-  remove_unused_states(simulation, states_info.particle_simulation_names);
-  reset_states(simulation);
-  add_missing_particle_states(simulation, states_info.particle_simulation_names);
+  remove_unused_states(simulation, required_states);
+  BKE_simulation_state_reset_all(simulation);
+  add_missing_states(simulation, required_states);
 }
 
 static void update_simulation_state_list(Simulation *simulation,
-                                         const SimulationStatesInfo &states_info)
+                                         const RequiredStates &required_states)
 {
-  remove_unused_states(simulation, states_info.particle_simulation_names);
-  add_missing_particle_states(simulation, states_info.particle_simulation_names);
+  remove_unused_states(simulation, required_states);
+  add_missing_states(simulation, required_states);
 }
 
 void update_simulation_in_depsgraph(Depsgraph *depsgraph,
@@ -139,13 +106,13 @@ void update_simulation_in_depsgraph(Depsgraph *depsgraph,
 
   ResourceCollector resources;
   SimulationInfluences influences;
-  SimulationStatesInfo states_info;
+  RequiredStates required_states;
 
   /* TODO: Use simulation_cow, but need to add depsgraph relations before that. */
-  collect_simulation_influences(*simulation_orig, resources, influences, states_info);
+  collect_simulation_influences(*simulation_orig, resources, influences, required_states);
 
   if (current_frame == 1) {
-    reinitialize_empty_simulation_states(simulation_orig, states_info);
+    reinitialize_empty_simulation_states(simulation_orig, required_states);
 
     initialize_simulation_states(*simulation_orig, *depsgraph, influences);
     simulation_orig->current_frame = 1;
@@ -153,7 +120,7 @@ void update_simulation_in_depsgraph(Depsgraph *depsgraph,
     copy_states_to_cow(simulation_orig, simulation_cow);
   }
   else if (current_frame == simulation_orig->current_frame + 1) {
-    update_simulation_state_list(simulation_orig, states_info);
+    update_simulation_state_list(simulation_orig, required_states);
 
     float time_step = 1.0f / 24.0f;
     solve_simulation_time_step(*simulation_orig, *depsgraph, influences, time_step);