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.

1 files changed, 26 insertions, 59 deletions

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);