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.

7 files changed, 70 insertions, 15 deletions

diff --git a/source/blender/functions/FN_multi_function.hh b/source/blender/functions/FN_multi_function.hh
index 77ab2749377..eaddcee7964 100644
--- a/source/blender/functions/FN_multi_function.hh
+++ b/source/blender/functions/FN_multi_function.hh
@@ -98,6 +98,11 @@ class MultiFunction {
     return signature_.function_name;
   }
 
+  bool depends_on_context() const
+  {
+    return signature_.depends_on_context;
+  }
+
   const MFSignature &signature() const
   {
     return signature_;
diff --git a/source/blender/functions/FN_multi_function_context.hh b/source/blender/functions/FN_multi_function_context.hh
index 3a448cc2c6e..8492fd86742 100644
--- a/source/blender/functions/FN_multi_function_context.hh
+++ b/source/blender/functions/FN_multi_function_context.hh
@@ -29,15 +29,39 @@
 
 #include "BLI_utildefines.h"
 
+#include "BLI_map.hh"
+
 namespace blender::fn {
 
+class MFContext;
+
 class MFContextBuilder {
+ private:
+  Map<std::string, const void *> global_contexts_;
+
+  friend MFContext;
+
+ public:
+  template<typename T> void add_global_context(std::string name, const T *context)
+  {
+    global_contexts_.add_new(std::move(name), (const void *)context);
+  }
 };
 
 class MFContext {
+ private:
+  MFContextBuilder &builder_;
+
  public:
-  MFContext(MFContextBuilder &UNUSED(builder))
+  MFContext(MFContextBuilder &builder) : builder_(builder)
+  {
+  }
+
+  template<typename T> const T *get_global_context(StringRef name) const
   {
+    const void *context = builder_.global_contexts_.lookup_default_as(name, nullptr);
+    /* TODO: Implement type checking. */
+    return (const T *)context;
   }
 };
 
diff --git a/source/blender/functions/FN_multi_function_network.hh b/source/blender/functions/FN_multi_function_network.hh
index f6d6c7417e7..20f8fb2ee43 100644
--- a/source/blender/functions/FN_multi_function_network.hh
+++ b/source/blender/functions/FN_multi_function_network.hh
@@ -95,7 +95,7 @@ class MFNode : NonCopyable, NonMovable {
   Span<MFOutputSocket *> outputs();
   Span<const MFOutputSocket *> outputs() const;
 
-  bool all_inputs_have_origin() const;
+  bool has_unlinked_inputs() const;
 
  private:
   void destruct_sockets();
@@ -341,14 +341,14 @@ inline Span<const MFOutputSocket *> MFNode::outputs() const
   return outputs_;
 }
 
-inline bool MFNode::all_inputs_have_origin() const
+inline bool MFNode::has_unlinked_inputs() const
 {
   for (const MFInputSocket *socket : inputs_) {
     if (socket->origin() == nullptr) {
-      return false;
+      return true;
     }
   }
-  return true;
+  return false;
 }
 
 /* --------------------------------------------------------------------
diff --git a/source/blender/functions/FN_multi_function_params.hh b/source/blender/functions/FN_multi_function_params.hh
index 9cce8bb7401..93d7b47af83 100644
--- a/source/blender/functions/FN_multi_function_params.hh
+++ b/source/blender/functions/FN_multi_function_params.hh
@@ -68,6 +68,10 @@ class MFParamsBuilder {
     virtual_array_spans_.append(ref);
   }
 
+  template<typename T> void add_uninitialized_single_output(T *value)
+  {
+    this->add_uninitialized_single_output(GMutableSpan(CPPType::get<T>(), value, 1));
+  }
   void add_uninitialized_single_output(GMutableSpan ref)
   {
     this->assert_current_param_type(MFParamType::ForSingleOutput(ref.type()));
diff --git a/source/blender/functions/FN_multi_function_signature.hh b/source/blender/functions/FN_multi_function_signature.hh
index af5f61fe2ee..26df7c98e4a 100644
--- a/source/blender/functions/FN_multi_function_signature.hh
+++ b/source/blender/functions/FN_multi_function_signature.hh
@@ -36,6 +36,7 @@ struct MFSignature {
   RawVector<std::string> param_names;
   RawVector<MFParamType> param_types;
   RawVector<int> param_data_indices;
+  bool depends_on_context = false;
 
   int data_index(int param_index) const
   {
@@ -157,6 +158,15 @@ class MFSignatureBuilder {
         break;
     }
   }
+
+  /* Context */
+
+  /** This indicates that the function accesses the context. This disables optimizations that
+   * depend on the fact that the function always performes the same operation. */
+  void depends_on_context()
+  {
+    data_.depends_on_context = true;
+  }
 };
 
 }  // namespace blender::fn
diff --git a/source/blender/functions/intern/multi_function_network_evaluation.cc b/source/blender/functions/intern/multi_function_network_evaluation.cc
index a7e1a2f42af..58577e31c42 100644
--- a/source/blender/functions/intern/multi_function_network_evaluation.cc
+++ b/source/blender/functions/intern/multi_function_network_evaluation.cc
@@ -230,7 +230,7 @@ BLI_NOINLINE void MFNetworkEvaluator::evaluate_network_to_compute_outputs(
     }
 
     BLI_assert(node.is_function());
-    BLI_assert(node.all_inputs_have_origin());
+    BLI_assert(!node.has_unlinked_inputs());
     const MFFunctionNode &function_node = node.as_function();
 
     bool all_origins_are_computed = true;
diff --git a/source/blender/functions/intern/multi_function_network_optimization.cc b/source/blender/functions/intern/multi_function_network_optimization.cc
index e76b2f51a15..f1e047f01a1 100644
--- a/source/blender/functions/intern/multi_function_network_optimization.cc
+++ b/source/blender/functions/intern/multi_function_network_optimization.cc
@@ -142,13 +142,24 @@ void dead_node_removal(MFNetwork &network)
  *
  * \{ */
 
+static bool function_node_can_be_constant(MFFunctionNode *node)
+{
+  if (node->has_unlinked_inputs()) {
+    return false;
+  }
+  if (node->function().depends_on_context()) {
+    return false;
+  }
+  return true;
+}
+
 static Vector<MFNode *> find_non_constant_nodes(MFNetwork &network)
 {
   Vector<MFNode *> non_constant_nodes;
   non_constant_nodes.extend(network.dummy_nodes());
 
   for (MFFunctionNode *node : network.function_nodes()) {
-    if (!node->all_inputs_have_origin()) {
+    if (!function_node_can_be_constant(node)) {
       non_constant_nodes.append(node);
     }
   }
@@ -319,17 +330,18 @@ void constant_folding(MFNetwork &network, ResourceCollector &resources)
 
 static uint64_t compute_node_hash(MFFunctionNode &node, RNG *rng, Span<uint64_t> node_hashes)
 {
+  if (node.function().depends_on_context()) {
+    return BLI_rng_get_uint(rng);
+  }
+  if (node.has_unlinked_inputs()) {
+    return BLI_rng_get_uint(rng);
+  }
+
   uint64_t combined_inputs_hash = 394659347u;
   for (MFInputSocket *input_socket : node.inputs()) {
     MFOutputSocket *origin_socket = input_socket->origin();
-    uint64_t input_hash;
-    if (origin_socket == nullptr) {
-      input_hash = BLI_rng_get_uint(rng);
-    }
-    else {
-      input_hash = BLI_ghashutil_combine_hash(node_hashes[origin_socket->node().id()],
-                                              origin_socket->index());
-    }
+    uint64_t input_hash = BLI_ghashutil_combine_hash(node_hashes[origin_socket->node().id()],
+                                                     origin_socket->index());
     combined_inputs_hash = BLI_ghashutil_combine_hash(combined_inputs_hash, input_hash);
   }