Constraints: introduce wrapper functions to access target lists.

Instead of directly accessing constraint-specific callbacks
in code all over blender, introduce two wrappers to retrieve
and free the target list.

This incidentally revealed a place within the Collada exporter
in BCAnimationSampler.cpp that didn't clean up after retrieving
the targets, resulting in a small memory leak. Fixing this should
be the only functional change in this commit.

This was split off from D9732.

Differential Revision: https://developer.blender.org/D13844

4 files changed, 59 insertions, 20 deletions

diff --git a/source/blender/blenkernel/BKE_constraint.h b/source/blender/blenkernel/BKE_constraint.h
index ce1f4c2b98c..737b05fee0c 100644
--- a/source/blender/blenkernel/BKE_constraint.h
+++ b/source/blender/blenkernel/BKE_constraint.h
@@ -307,6 +307,25 @@ void BKE_constraint_target_matrix_get(struct Depsgraph *depsgraph,
                                       void *ownerdata,
                                       float mat[4][4],
                                       float ctime);
+
+/**
+ * Retrieves the list of all constraint targets, including the custom space target.
+ * Must be followed by a call to BKE_constraint_targets_flush to free memory.
+ *
+ * \param r_targets Pointer to the list to be initialized with target data.
+ * \returns the number of targets stored in the list.
+ */
+int BKE_constraint_targets_get(struct bConstraint *con, struct ListBase *r_targets);
+
+/**
+ * Copies changed data from the list produced by BKE_constraint_targets_get back to the constraint
+ * data structures and frees memory.
+ *
+ * \param targets List of targets filled by BKE_constraint_targets_get.
+ * \param no_copy Only free memory without copying changes (read-only mode).
+ */
+void BKE_constraint_targets_flush(struct bConstraint *con, struct ListBase *targets, bool no_copy);
+
 /**
  * Get the list of targets required for solving a constraint.
  */
diff --git a/source/blender/blenkernel/intern/action.c b/source/blender/blenkernel/intern/action.c
index 371bd8ded6d..05b51e0c9fa 100644
--- a/source/blender/blenkernel/intern/action.c
+++ b/source/blender/blenkernel/intern/action.c
@@ -980,13 +980,10 @@ void BKE_pose_channels_remove(Object *ob,
       else {
         /* Maybe something the bone references is being removed instead? */
         for (con = pchan->constraints.first; con; con = con->next) {
-          const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
           ListBase targets = {NULL, NULL};
           bConstraintTarget *ct;
 
-          if (cti && cti->get_constraint_targets) {
-            cti->get_constraint_targets(con, &targets);
-
+          if (BKE_constraint_targets_get(con, &targets)) {
             for (ct = targets.first; ct; ct = ct->next) {
               if (ct->tar == ob) {
                 if (ct->subtarget[0]) {
@@ -998,9 +995,7 @@ void BKE_pose_channels_remove(Object *ob,
               }
             }
 
-            if (cti->flush_constraint_targets) {
-              cti->flush_constraint_targets(con, &targets, 0);
-            }
+            BKE_constraint_targets_flush(con, &targets, 0);
           }
         }
 
diff --git a/source/blender/blenkernel/intern/constraint.c b/source/blender/blenkernel/intern/constraint.c
index 35f2f94bc91..6ffb3299869 100644
--- a/source/blender/blenkernel/intern/constraint.c
+++ b/source/blender/blenkernel/intern/constraint.c
@@ -6191,6 +6191,40 @@ bool BKE_constraint_is_nonlocal_in_liboverride(const Object *ob, const bConstrai
 
 /* -------- Target-Matrix Stuff ------- */
 
+int BKE_constraint_targets_get(struct bConstraint *con, struct ListBase *r_targets)
+{
+  BLI_listbase_clear(r_targets);
+
+  const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
+
+  if (!cti) {
+    return 0;
+  }
+
+  int count = 0;
+
+  /* Constraint-specific targets. */
+  if (cti->get_constraint_targets) {
+    count = cti->get_constraint_targets(con, r_targets);
+  }
+
+  return count;
+}
+
+void BKE_constraint_targets_flush(struct bConstraint *con, struct ListBase *targets, bool no_copy)
+{
+  const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
+
+  if (!cti) {
+    return;
+  }
+
+  /* Release the constraint-specific targets. */
+  if (cti->flush_constraint_targets) {
+    cti->flush_constraint_targets(con, targets, no_copy);
+  }
+}
+
 void BKE_constraint_target_matrix_get(struct Depsgraph *depsgraph,
                                       Scene *scene,
                                       bConstraint *con,
diff --git a/source/blender/blenkernel/intern/object.cc b/source/blender/blenkernel/intern/object.cc
index 52b25399e32..c8b87c27697 100644
--- a/source/blender/blenkernel/intern/object.cc
+++ b/source/blender/blenkernel/intern/object.cc
@@ -2483,21 +2483,16 @@ static void copy_object_pose(Object *obn, const Object *ob, const int flag)
      *     BKE_library_remap stuff, but...
      *     the flush_constraint_targets callback am not sure about, so will delay that for now. */
     LISTBASE_FOREACH (bConstraint *, con, &chan->constraints) {
-      const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
       ListBase targets = {nullptr, nullptr};
 
-      if (cti && cti->get_constraint_targets) {
-        cti->get_constraint_targets(con, &targets);
-
+      if (BKE_constraint_targets_get(con, &targets)) {
         LISTBASE_FOREACH (bConstraintTarget *, ct, &targets) {
           if (ct->tar == ob) {
             ct->tar = obn;
           }
         }
 
-        if (cti->flush_constraint_targets) {
-          cti->flush_constraint_targets(con, &targets, false);
-        }
+        BKE_constraint_targets_flush(con, &targets, false);
       }
     }
   }
@@ -5488,11 +5483,9 @@ bool BKE_object_modifier_update_subframe(Depsgraph *depsgraph,
 
     /* also update constraint targets */
     LISTBASE_FOREACH (bConstraint *, con, &ob->constraints) {
-      const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
       ListBase targets = {nullptr, nullptr};
 
-      if (cti && cti->get_constraint_targets) {
-        cti->get_constraint_targets(con, &targets);
+      if (BKE_constraint_targets_get(con, &targets)) {
         LISTBASE_FOREACH (bConstraintTarget *, ct, &targets) {
           if (ct->tar) {
             BKE_object_modifier_update_subframe(
@@ -5500,9 +5493,7 @@ bool BKE_object_modifier_update_subframe(Depsgraph *depsgraph,
           }
         }
         /* free temp targets */
-        if (cti->flush_constraint_targets) {
-          cti->flush_constraint_targets(con, &targets, false);
-        }
+        BKE_constraint_targets_flush(con, &targets, false);
       }
     }
   }