Particles: initial object socket and emitter node support

Object sockets work now, but only the new Object Transforms and the
Particle Mesh Emitter node use it. The emitter does not actually
use the mesh surface yet. Instead, new particles are just emitted around
the origin of the object.

Internally, handles to object data blocks are passed around in the network,
instead of raw object pointers. Using handles has a couple of benefits:
* The caller of the function has control over which handles can be resolved
  and therefore limit access to specific data. The set of data blocks that
  is accessed by a node tree should be known statically. This is necessary
  for a proper integration with the dependency graph.
* When the pointer to an object changes (e.g. after restarting Blender),
  all handles are still valid.
* When an object is deleted, the handle is invalidated without causing crashes.
* The handle is just an integer that can be stored per particle and can be cached easily.

The mapping between handles and their corresponding data blocks is
stored in the Simulation data block.

5 files changed, 241 insertions, 39 deletions

diff --git a/source/blender/simulation/intern/particle_function.cc b/source/blender/simulation/intern/particle_function.cc
index e0de68d9b29..935ef7983d9 100644
--- a/source/blender/simulation/intern/particle_function.cc
+++ b/source/blender/simulation/intern/particle_function.cc
@@ -50,12 +50,18 @@ ParticleFunction::ParticleFunction(const fn::MultiFunction *global_fn,
 }
 
 ParticleFunctionEvaluator::ParticleFunctionEvaluator(
-    const ParticleFunction &particle_fn, const ParticleChunkContext &particle_chunk_context)
+    const ParticleFunction &particle_fn,
+    const SimulationSolveContext &solve_context,
+    const ParticleChunkContext &particle_chunk_context)
     : particle_fn_(particle_fn),
+      solve_context_(solve_context),
       particle_chunk_context_(particle_chunk_context),
       mask_(particle_chunk_context_.index_mask()),
       outputs_(particle_fn_.output_types_.size(), nullptr)
 {
+  global_context_.add_global_context("PersistentDataHandleMap", &solve_context_.handle_map());
+  per_particle_context_.add_global_context("PersistentDataHandleMap",
+                                           &solve_context_.handle_map());
 }
 
 ParticleFunctionEvaluator::~ParticleFunctionEvaluator()
diff --git a/source/blender/simulation/intern/particle_function.hh b/source/blender/simulation/intern/particle_function.hh
index bbb40efb388..eec4a700383 100644
--- a/source/blender/simulation/intern/particle_function.hh
+++ b/source/blender/simulation/intern/particle_function.hh
@@ -60,6 +60,7 @@ class ParticleFunctionEvaluator {
  private:
   ResourceCollector resources_;
   const ParticleFunction &particle_fn_;
+  const SimulationSolveContext &solve_context_;
   const ParticleChunkContext &particle_chunk_context_;
   IndexMask mask_;
   fn::MFContextBuilder global_context_;
@@ -69,6 +70,7 @@ class ParticleFunctionEvaluator {
 
  public:
   ParticleFunctionEvaluator(const ParticleFunction &particle_fn,
+                            const SimulationSolveContext &solve_context,
                             const ParticleChunkContext &particle_chunk_context);
   ~ParticleFunctionEvaluator();
 
diff --git a/source/blender/simulation/intern/simulation_collect_influences.cc b/source/blender/simulation/intern/simulation_collect_influences.cc
index d4161b06a00..4760063daca 100644
--- a/source/blender/simulation/intern/simulation_collect_influences.cc
+++ b/source/blender/simulation/intern/simulation_collect_influences.cc
@@ -50,31 +50,51 @@ static Span<const nodes::DNode *> get_particle_simulation_nodes(const nodes::Der
   return tree.nodes_by_type("SimulationNodeParticleSimulation");
 }
 
-static std::optional<Array<std::string>> compute_global_string_inputs(
-    nodes::MFNetworkTreeMap &network_map, Span<const fn::MFInputSocket *> sockets)
+/* Returns true on success. */
+static bool compute_global_inputs(nodes::MFNetworkTreeMap &network_map,
+                                  ResourceCollector &resources,
+                                  Span<const fn::MFInputSocket *> sockets,
+                                  MutableSpan<fn::GMutableSpan> r_results)
 {
   int amount = sockets.size();
   if (amount == 0) {
-    return Array<std::string>();
+    return true;
   }
 
   if (network_map.network().have_dummy_or_unlinked_dependencies(sockets)) {
-    return {};
+    return false;
   }
 
   fn::MFNetworkEvaluator network_fn{{}, sockets};
-
   fn::MFParamsBuilder params{network_fn, 1};
-
-  Array<std::string> strings(amount, NoInitialization());
-  for (int i : IndexRange(amount)) {
-    params.add_uninitialized_single_output(
-        fn::GMutableSpan(fn::CPPType::get<std::string>(), strings.data() + i, 1));
+  for (int param_index : network_fn.param_indices()) {
+    fn::MFParamType param_type = network_fn.param_type(param_index);
+    BLI_assert(param_type.category() == fn::MFParamType::Category::SingleOutput); /* For now. */
+    const fn::CPPType &type = param_type.data_type().single_type();
+    void *buffer = resources.linear_allocator().allocate(type.size(), type.alignment());
+    resources.add(buffer, type.destruct_cb(), AT);
+    fn::GMutableSpan span{type, buffer, 1};
+    r_results[param_index] = span;
+    params.add_uninitialized_single_output(span);
   }
-
   fn::MFContextBuilder context;
-  network_fn.call({0}, params, context);
+  network_fn.call(IndexRange(1), params, context);
+  return true;
+}
 
+static std::optional<Array<std::string>> compute_global_string_inputs(
+    nodes::MFNetworkTreeMap &network_map, Span<const fn::MFInputSocket *> sockets)
+{
+  ResourceCollector local_resources;
+  Array<fn::GMutableSpan> computed_values(sockets.size(), NoInitialization());
+  if (!compute_global_inputs(network_map, local_resources, sockets, computed_values)) {
+    return {};
+  }
+
+  Array<std::string> strings(sockets.size());
+  for (int i : sockets.index_range()) {
+    strings[i] = std::move(computed_values[i].typed<std::string>()[0]);
+  }
   return strings;
 }
 
@@ -203,7 +223,8 @@ class ParticleFunctionForce : public ParticleForce {
     IndexMask mask = context.particle_chunk().index_mask();
     MutableSpan<float3> r_combined_force = context.force_dst();
 
-    ParticleFunctionEvaluator evaluator{particle_fn_, context.particle_chunk()};
+    ParticleFunctionEvaluator evaluator{
+        particle_fn_, context.solve_context(), context.particle_chunk()};
     evaluator.compute();
     fn::VSpan<float3> forces = evaluator.get<float3>(0, "Force");
 
@@ -258,44 +279,120 @@ static void collect_forces(nodes::MFNetworkTreeMap &network_map,
 
 class MyBasicEmitter : public ParticleEmitter {
  private:
-  std::string name_;
+  Array<std::string> names_;
+  const fn::MultiFunction &inputs_fn_;
+  uint32_t seed_;
 
  public:
-  MyBasicEmitter(std::string name) : name_(std::move(name))
+  MyBasicEmitter(Array<std::string> names, const fn::MultiFunction &inputs_fn, uint32_t seed)
+      : names_(std::move(names)), inputs_fn_(inputs_fn), seed_(seed)
   {
   }
 
   void emit(ParticleEmitterContext &context) const override
   {
-    ParticleAllocator *allocator = context.try_get_particle_allocator(name_);
-    if (allocator == nullptr) {
+    fn::MFContextBuilder mf_context;
+    mf_context.add_global_context("PersistentDataHandleMap",
+                                  &context.solve_context().handle_map());
+
+    fn::MFParamsBuilder mf_params{inputs_fn_, 1};
+    bke::PersistentObjectHandle object_handle;
+    float rate;
+    mf_params.add_uninitialized_single_output(&object_handle);
+    mf_params.add_uninitialized_single_output(&rate);
+    inputs_fn_.call(IndexRange(1), mf_params, mf_context);
+
+    const Object *object = context.solve_context().handle_map().lookup(object_handle);
+    if (object == nullptr) {
       return;
     }
 
-    fn::MutableAttributesRef attributes = allocator->allocate(10);
-    RandomNumberGenerator rng{(uint32_t)context.simulation_time_interval().start() ^
-                              (uint32_t)DefaultHash<std::string>{}(name_)};
+    Vector<float3> new_positions;
+    Vector<float3> new_velocities;
+    Vector<float> new_birth_times;
+
+    float start_time = context.simulation_time_interval().start();
+    RandomNumberGenerator rng{(*(uint32_t *)&start_time) ^ seed_};
+
+    int amount = rate * 10;
+    for (int i : IndexRange(amount)) {
+      UNUSED_VARS(i);
+      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());
+    }
+
+    for (StringRef name : names_) {
+      ParticleAllocator *allocator = context.try_get_particle_allocator(name);
+      if (allocator == nullptr) {
+        return;
+      }
 
-    MutableSpan<float3> positions = attributes.get<float3>("Position");
-    MutableSpan<float3> velocities = attributes.get<float3>("Velocity");
-    MutableSpan<float> birth_times = attributes.get<float>("Birth Time");
+      fn::MutableAttributesRef attributes = allocator->allocate(amount);
 
-    for (int i : IndexRange(attributes.size())) {
-      positions[i] = rng.get_unit_float3();
-      velocities[i] = rng.get_unit_float3();
-      birth_times[i] = context.simulation_time_interval().start();
+      initialized_copy_n(new_positions.data(), amount, attributes.get<float3>("Position").data());
+      initialized_copy_n(new_velocities.data(), amount, attributes.get<float3>("Velocity").data());
+      initialized_copy_n(
+          new_birth_times.data(), amount, attributes.get<float>("Birth Time").data());
     }
   }
 };
 
+static Vector<const nodes::DNode *> find_linked_particle_simulations(
+    const nodes::DOutputSocket &output_socket)
+{
+  Vector<const nodes::DNode *> simulation_nodes;
+  for (const nodes::DInputSocket *target_socket : output_socket.linked_sockets()) {
+    if (target_socket->node().idname() == "SimulationNodeParticleSimulation") {
+      simulation_nodes.append(&target_socket->node());
+    }
+  }
+  return simulation_nodes;
+}
+
+static ParticleEmitter *create_particle_emitter(const nodes::DNode &dnode,
+                                                ResourceCollector &resources,
+                                                nodes::MFNetworkTreeMap &network_map)
+{
+  Vector<const nodes::DNode *> simulation_dnodes = find_linked_particle_simulations(
+      dnode.output(0));
+  if (simulation_dnodes.size() == 0) {
+    return nullptr;
+  }
+
+  Array<std::string> names{simulation_dnodes.size()};
+  for (int i : simulation_dnodes.index_range()) {
+    names[i] = dnode_to_path(*simulation_dnodes[i]);
+  }
+
+  Array<const fn::MFInputSocket *> input_sockets{dnode.inputs().size()};
+  for (int i : input_sockets.index_range()) {
+    input_sockets[i] = &network_map.lookup_dummy(dnode.input(i));
+  }
+
+  if (network_map.network().have_dummy_or_unlinked_dependencies(input_sockets)) {
+    return nullptr;
+  }
+
+  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));
+  ParticleEmitter &emitter = resources.construct<MyBasicEmitter>(
+      AT, std::move(names), inputs_fn, seed);
+  return &emitter;
+}
+
 static void collect_emitters(nodes::MFNetworkTreeMap &network_map,
                              ResourceCollector &resources,
                              SimulationInfluences &r_influences)
 {
-  for (const nodes::DNode *dnode : get_particle_simulation_nodes(network_map.tree())) {
-    std::string name = dnode_to_path(*dnode);
-    ParticleEmitter &emitter = resources.construct<MyBasicEmitter>(AT, name);
-    r_influences.particle_emitters.append(&emitter);
+  for (const nodes::DNode *dnode :
+       network_map.tree().nodes_by_type("SimulationNodeParticleMeshEmitter")) {
+    ParticleEmitter *emitter = create_particle_emitter(*dnode, resources, network_map);
+    if (emitter != nullptr) {
+      r_influences.particle_emitters.append(emitter);
+    }
   }
 }
 
@@ -316,6 +413,23 @@ static void prepare_particle_attribute_builders(nodes::MFNetworkTreeMap &network
   }
 }
 
+static void find_used_data_blocks(const nodes::DerivedNodeTree &tree,
+                                  SimulationInfluences &r_influences)
+{
+  const bNodeSocketType *socktype = nodeSocketTypeFind("NodeSocketObject");
+  BLI_assert(socktype != nullptr);
+
+  for (const nodes::DInputSocket *dsocket : tree.input_sockets()) {
+    const bNodeSocket *bsocket = dsocket->bsocket();
+    if (bsocket->typeinfo == socktype) {
+      Object *value = ((const bNodeSocketValueObject *)bsocket->default_value)->value;
+      if (value != nullptr) {
+        r_influences.used_data_blocks.add(&value->id);
+      }
+    }
+  }
+}
+
 void collect_simulation_influences(Simulation &simulation,
                                    ResourceCollector &resources,
                                    SimulationInfluences &r_influences,
@@ -343,6 +457,8 @@ void collect_simulation_influences(Simulation &simulation,
   for (const nodes::DNode *dnode : get_particle_simulation_nodes(tree)) {
     r_states_info.particle_simulation_names.add(dnode_to_path(*dnode));
   }
+
+  find_used_data_blocks(tree, r_influences);
 }
 
 }  // namespace blender::sim
diff --git a/source/blender/simulation/intern/simulation_solver.cc b/source/blender/simulation/intern/simulation_solver.cc
index f542d6ab2c8..158c50957df 100644
--- a/source/blender/simulation/intern/simulation_solver.cc
+++ b/source/blender/simulation/intern/simulation_solver.cc
@@ -17,8 +17,11 @@
 #include "simulation_solver.hh"
 
 #include "BKE_customdata.h"
+#include "BKE_lib_id.h"
+#include "BKE_persistent_data_handle.hh"
 
 #include "BLI_rand.hh"
+#include "BLI_set.hh"
 
 namespace blender::sim {
 
@@ -243,6 +246,53 @@ BLI_NOINLINE static void remove_dead_and_add_new_particles(ParticleSimulationSta
   state.next_particle_id += allocator.total_allocated();
 }
 
+static void update_persistent_data_handles(Simulation &simulation,
+                                           const VectorSet<ID *> &used_data_blocks)
+{
+  Set<ID *> contained_ids;
+  Set<int> used_handles;
+
+  /* Remove handles that have been invalidated. */
+  LISTBASE_FOREACH_MUTABLE (
+      PersistentDataHandleItem *, handle_item, &simulation.persistent_data_handles) {
+    if (handle_item->id == nullptr) {
+      BLI_remlink(&simulation.persistent_data_handles, handle_item);
+      continue;
+    }
+    if (!used_data_blocks.contains(handle_item->id)) {
+      id_us_min(handle_item->id);
+      BLI_remlink(&simulation.persistent_data_handles, handle_item);
+      MEM_freeN(handle_item);
+      continue;
+    }
+    contained_ids.add_new(handle_item->id);
+    used_handles.add_new(handle_item->handle);
+  }
+
+  /* Add new handles that are not in the list yet. */
+  int next_handle = 0;
+  for (ID *id : used_data_blocks) {
+    if (contained_ids.contains(id)) {
+      continue;
+    }
+
+    /* Find the next available handle. */
+    while (used_handles.contains(next_handle)) {
+      next_handle++;
+    }
+    used_handles.add_new(next_handle);
+
+    PersistentDataHandleItem *handle_item = (PersistentDataHandleItem *)MEM_callocN(
+        sizeof(*handle_item), AT);
+    /* Cannot store const pointers in DNA. */
+    id_us_plus(id);
+    handle_item->id = id;
+    handle_item->handle = next_handle;
+
+    BLI_addtail(&simulation.persistent_data_handles, handle_item);
+  }
+}
+
 void initialize_simulation_states(Simulation &simulation,
                                   Depsgraph &UNUSED(depsgraph),
                                   const SimulationInfluences &UNUSED(influences))
@@ -255,11 +305,18 @@ void solve_simulation_time_step(Simulation &simulation,
                                 const SimulationInfluences &influences,
                                 float time_step)
 {
-  SimulationSolveContext solve_context{
-      simulation,
-      depsgraph,
-      influences,
-      TimeInterval(simulation.current_simulation_time, time_step)};
+  update_persistent_data_handles(simulation, influences.used_data_blocks);
+
+  bke::PersistentDataHandleMap handle_map;
+  LISTBASE_FOREACH (PersistentDataHandleItem *, handle, &simulation.persistent_data_handles) {
+    handle_map.add(handle->handle, *handle->id);
+  }
+
+  SimulationSolveContext solve_context{simulation,
+                                       depsgraph,
+                                       influences,
+                                       TimeInterval(simulation.current_simulation_time, time_step),
+                                       handle_map};
   TimeInterval simulation_time_interval{simulation.current_simulation_time, time_step};
 
   Vector<SimulationState *> simulation_states{simulation.states};
diff --git a/source/blender/simulation/intern/simulation_solver.hh b/source/blender/simulation/intern/simulation_solver.hh
index b5e42b53846..1d1b9935661 100644
--- a/source/blender/simulation/intern/simulation_solver.hh
+++ b/source/blender/simulation/intern/simulation_solver.hh
@@ -24,6 +24,8 @@
 
 #include "FN_attributes_ref.hh"
 
+#include "BKE_persistent_data_handle.hh"
+
 #include "particle_allocator.hh"
 #include "time_interval.hh"
 
@@ -50,6 +52,7 @@ struct SimulationInfluences {
   Map<std::string, Vector<const ParticleForce *>> particle_forces;
   Map<std::string, fn::AttributesInfoBuilder *> particle_attributes_builder;
   Vector<const ParticleEmitter *> particle_emitters;
+  VectorSet<ID *> used_data_blocks;
 };
 
 class SimulationSolveContext {
@@ -58,16 +61,19 @@ class SimulationSolveContext {
   Depsgraph &depsgraph_;
   const SimulationInfluences &influences_;
   TimeInterval solve_interval_;
+  const bke::PersistentDataHandleMap &id_handle_map_;
 
  public:
   SimulationSolveContext(Simulation &simulation,
                          Depsgraph &depsgraph,
                          const SimulationInfluences &influences,
-                         TimeInterval solve_interval)
+                         TimeInterval solve_interval,
+                         const bke::PersistentDataHandleMap &handle_map)
       : simulation_(simulation),
         depsgraph_(depsgraph),
         influences_(influences),
-        solve_interval_(solve_interval)
+        solve_interval_(solve_interval),
+        id_handle_map_(handle_map)
   {
   }
 
@@ -80,6 +86,11 @@ class SimulationSolveContext {
   {
     return influences_;
   }
+
+  const bke::PersistentDataHandleMap &handle_map() const
+  {
+    return id_handle_map_;
+  }
 };
 
 class ParticleAllocators {
@@ -147,6 +158,11 @@ class ParticleEmitterContext {
   {
   }
 
+  SimulationSolveContext &solve_context()
+  {
+    return solve_context_;
+  }
+
   ParticleAllocator *try_get_particle_allocator(StringRef particle_simulation_name)
   {
     return particle_allocators_.try_get_allocator(particle_simulation_name);
@@ -174,6 +190,11 @@ class ParticleForceContext {
   {
   }
 
+  SimulationSolveContext &solve_context()
+  {
+    return solve_context_;
+  }
+
   const ParticleChunkContext &particle_chunk() const
   {
     return particle_chunk_context_;