deg_builder_relations_drivers.cc

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/* SPDX-FileCopyrightText: 2013 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#include "intern/builder/deg_builder_relations_drivers.h"
 
#include <cstring>
 
#include "BLI_listbase.h"
 
#include "DNA_anim_types.h"
 
#include "BKE_anim_data.hh"
 
#include "intern/builder/deg_builder_relations.h"
#include "intern/depsgraph_relation.hh"
#include "intern/node/deg_node.hh"
 
namespace blender::deg {
 
DriverDescriptor::DriverDescriptor(PointerRNA *id_ptr, FCurve *fcu)
    : id_ptr_(id_ptr),
      fcu_(fcu),
      driver_relations_needed_(false),
      pointer_rna_(),
      property_rna_(nullptr),
      is_array_(false)
{
  driver_relations_needed_ = determine_relations_needed();
  split_rna_path();
}
 
bool DriverDescriptor::determine_relations_needed()
{
  if (fcu_->array_index > 0) {
    /* Drivers on array elements always need relations. */
    is_array_ = true;
    return true;
  }
 
  if (!resolve_rna()) {
    /* Properties that don't exist can't cause threading issues either. */
    return false;
  }
 
  if (RNA_property_array_check(property_rna_)) {
    /* Drivers on array elements always need relations. */
    is_array_ = true;
    return true;
  }
 
  /* Drivers on Booleans and Enums (when used as bitflags) can write to the same memory location,
   * so they need relations between each other. */
  return ELEM(RNA_property_type(property_rna_), PROP_BOOLEAN, PROP_ENUM);
}
 
bool DriverDescriptor::driver_relations_needed() const
{
  return driver_relations_needed_;
}
 
bool DriverDescriptor::is_array() const
{
  return is_array_;
}
 
bool DriverDescriptor::is_same_array_as(const DriverDescriptor &other) const
{
  if (!is_array_ || !other.is_array_) {
    return false;
  }
  return rna_suffix == other.rna_suffix;
}
 
OperationKey DriverDescriptor::depsgraph_key() const
{
  return OperationKey(id_ptr_->owner_id,
                      NodeType::PARAMETERS,
                      OperationCode::DRIVER,
                      fcu_->rna_path,
                      fcu_->array_index);
}
 
void DriverDescriptor::split_rna_path()
{
  const char *last_dot = strrchr(fcu_->rna_path, '.');
  if (last_dot == nullptr || last_dot[1] == '\0') {
    rna_prefix = StringRef();
    rna_suffix = StringRef(fcu_->rna_path);
    return;
  }
 
  rna_prefix = StringRef(fcu_->rna_path, last_dot);
  rna_suffix = StringRef(last_dot + 1);
}
 
bool DriverDescriptor::resolve_rna()
{
  return RNA_path_resolve_property(id_ptr_, fcu_->rna_path, &pointer_rna_, &property_rna_);
}
 
static bool is_reachable(const Node *const from, const Node *const to)
{
  if (from == to) {
    return true;
  }
 
  /* Perform a graph walk from 'to' towards its incoming connections.
   * Walking from 'from' towards its outgoing connections is 10x slower on the Spring rig. */
  deque<const Node *> queue;
  Set<const Node *> seen;
  queue.push_back(to);
  while (!queue.empty()) {
    /* Visit the next node to inspect. */
    const Node *visit = queue.back();
    queue.pop_back();
 
    if (visit == from) {
      return true;
    }
 
    /* Queue all incoming relations that we haven't seen before. */
    for (Relation *relation : visit->inlinks) {
      const Node *prev_node = relation->from;
      if (seen.add(prev_node)) {
        queue.push_back(prev_node);
      }
    }
  }
  return false;
}
 
/* **** DepsgraphRelationBuilder functions **** */
 
void DepsgraphRelationBuilder::build_driver_relations()
{
  for (IDNode *id_node : graph_->id_nodes) {
    build_driver_relations(id_node);
  }
}
 
void DepsgraphRelationBuilder::build_driver_relations(IDNode *id_node)
{
  /* Add relations between drivers that write to the same datablock.
   *
   * This prevents threading issues when two separate RNA properties write to
   * the same memory address. For example:
   * - Drivers on individual array elements, as the animation system will write
   *   the whole array back to RNA even when changing individual array value.
   * - Drivers on RNA properties that map to a single bit flag. Changing the RNA
   *   value will write the entire int containing the bit, in a non-thread-safe
   *   way.
   */
  ID *id_orig = id_node->id_orig;
  AnimData *adt = BKE_animdata_from_id(id_orig);
  if (adt == nullptr) {
    return;
  }
 
  /* Mapping from RNA prefix -> set of driver descriptors: */
  Map<string, Vector<DriverDescriptor>> driver_groups;
 
  PointerRNA id_ptr = RNA_id_pointer_create(id_orig);
 
  LISTBASE_FOREACH (FCurve *, fcu, &adt->drivers) {
    if (fcu->rna_path == nullptr) {
      continue;
    }
 
    DriverDescriptor driver_desc(&id_ptr, fcu);
    if (!driver_desc.driver_relations_needed()) {
      continue;
    }
 
    driver_groups.lookup_or_add_default_as(driver_desc.rna_prefix).append(driver_desc);
  }
 
  for (Span<DriverDescriptor> prefix_group : driver_groups.values()) {
    /* For each node in the driver group, try to connect it to another node
     * in the same group without creating any cycles. */
    int num_drivers = prefix_group.size();
    if (num_drivers < 2) {
      /* A relation requires two drivers. */
      continue;
    }
    for (int from_index = 0; from_index < num_drivers; ++from_index) {
      const DriverDescriptor &driver_from = prefix_group[from_index];
      Node *op_from = get_node(driver_from.depsgraph_key());
 
      /* Start by trying the next node in the group. */
      for (int to_offset = 1; to_offset < num_drivers; ++to_offset) {
        const int to_index = (from_index + to_offset) % num_drivers;
        const DriverDescriptor &driver_to = prefix_group[to_index];
        Node *op_to = get_node(driver_to.depsgraph_key());
 
        /* Duplicate drivers can exist (see #78615), but cannot be distinguished by OperationKey
         * and thus have the same depsgraph node. Relations between those drivers should not be
         * created. This not something that is expected to happen (both the UI and the Python API
         * prevent duplicate drivers), it did happen in a file and it is easy to deal with here. */
        if (op_from == op_to) {
          continue;
        }
 
        if (from_index < to_index && driver_from.is_same_array_as(driver_to)) {
          /* This is for adding a relation like `color[0]` -> `color[1]`.
           * When the search for another driver wraps around,
           * we cannot blindly add relations any more. */
        }
        else {
          /* Investigate whether this relation would create a dependency cycle.
           * Example graph:
           *     A -> B -> C
           * and investigating a potential connection C->A. Because A->C is an
           * existing transitive connection, adding C->A would create a cycle. */
          if (is_reachable(op_to, op_from)) {
            continue;
          }
 
          /* No need to directly connect this node if there is already a transitive connection. */
          if (is_reachable(op_from, op_to)) {
            break;
          }
        }
 
        add_operation_relation(
            op_from->get_exit_operation(), op_to->get_entry_operation(), "Driver Serialization");
        break;
      }
    }
  }
}
 
}  // namespace blender::deg