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.

4 files changed, 226 insertions, 158 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;
+}