Fix T73051: Multiple IK chains influencing the same bone don't work

This patch fixes {T73051}. The cause of the issue was the absence of
relations in the depsgraph between IK solvers of overlapping IK chains.

Reviewed By: sergey, brecht

Differential Revision: https://developer.blender.org/D6700

source/blender/depsgraph/intern/builder/deg_builder_pchanmap.cc

@@ -91,7 +91,7 @@ void RootPChanMap::add_bone(const char *bone, const char *root)
 }
 
 /* Check if there's a common root bone between two bones. */
-bool RootPChanMap::has_common_root(const char *bone1, const char *bone2)
+bool RootPChanMap::has_common_root(const char *bone1, const char *bone2) const
 {
   /* Ensure that both are in the map... */
   if (BLI_ghash_haskey(map_, bone1) == false) {

source/blender/depsgraph/intern/builder/deg_builder_pchanmap.h

@@ -39,7 +39,7 @@ struct RootPChanMap {
   void add_bone(const char *bone, const char *root);
 
   /* Check if there's a common root bone between two bones. */
-  bool has_common_root(const char *bone1, const char *bone2);
+  bool has_common_root(const char *bone1, const char *bone2) const;
 
  protected:
   /* The actual map:

source/blender/depsgraph/intern/builder/deg_builder_relations.cc

@@ -203,7 +203,7 @@ bool check_id_has_anim_component(ID *id)
 bool check_id_has_driver_component(ID *id)
 {
   AnimData *adt = BKE_animdata_from_id(id);
-  if (adt == nullptr) {
+  if (adt == NULL) {
     return false;
   }
   return !BLI_listbase_is_empty(&adt->drivers);

source/blender/depsgraph/intern/builder/deg_builder_relations.h

@@ -257,6 +257,10 @@ class DepsgraphRelationBuilder : public DepsgraphBuilder {
                                    bPoseChannel *pchan,
                                    bConstraint *con,
                                    RootPChanMap *root_map);
+  virtual void build_inter_ik_chains(Object *object,
+                                     const OperationKey &solver_key,
+                                     const bPoseChannel *rootchan,
+                                     const RootPChanMap *root_map);
   virtual void build_rig(Object *object);
   virtual void build_proxy_rig(Object *object);
   virtual void build_shapekeys(Key *key);

source/blender/depsgraph/intern/builder/deg_builder_relations_rig.cc

@@ -192,6 +192,9 @@ void DepsgraphRelationBuilder::build_ik_pose(Object *object,
   }
   OperationKey pose_done_key(&object->id, NodeType::EVAL_POSE, OperationCode::POSE_DONE);
   add_relation(solver_key, pose_done_key, "PoseEval Result-Bone Link");
+
+  /* Add relation when the root of this IK chain is influenced by another IK chain. */
+  build_inter_ik_chains(object, solver_key, rootchan, root_map);
 }
 
 /* Spline IK Eval Steps */
@@ -244,6 +247,33 @@ void DepsgraphRelationBuilder::build_splineik_pose(Object *object,
   }
   OperationKey pose_done_key(&object->id, NodeType::EVAL_POSE, OperationCode::POSE_DONE);
   add_relation(solver_key, pose_done_key, "PoseEval Result-Bone Link");
+
+  /* Add relation when the root of this IK chain is influenced by another IK chain. */
+  build_inter_ik_chains(object, solver_key, rootchan, root_map);
+}
+
+void DepsgraphRelationBuilder::build_inter_ik_chains(Object *object,
+                                                     const OperationKey &solver_key,
+                                                     const bPoseChannel *rootchan,
+                                                     const RootPChanMap *root_map)
+{
+  bPoseChannel *deepest_root = NULL;
+  const char *root_name = rootchan->name;
+
+  /* Find shared IK chain root. */
+  for (bPoseChannel *parchan = rootchan->parent; parchan; parchan = parchan->parent) {
+    if (!root_map->has_common_root(root_name, parchan->name)) {
+      break;
+    }
+    deepest_root = parchan;
+  }
+  if (deepest_root == NULL) {
+    return;
+  }
+
+  OperationKey other_bone_key(
+      &object->id, NodeType::BONE, deepest_root->name, OperationCode::BONE_DONE);
+  add_relation(other_bone_key, solver_key, "IK Chain Overlap");
 }
 
 /* Pose/Armature Bones Graph */