Refactor the Custom Space patch.

Instead of modifying all the get_constraint_targets and flush_constraint_targets callbacks, introduce wrapper API functions and handle the new reference there. Also, it is not needed to do all the target dance to compute the space_obj_world_matrix.
Add Custom Space to Constraints
2020-11-23 23:42:05 +03:00 · 2020-11-23 19:37:20 +03:00
20 changed files with 458 additions and 205 deletions
--- a/release/scripts/startup/bl_ui/properties_constraint.py
+++ b/release/scripts/startup/bl_ui/properties_constraint.py
@@ -85,14 +85,23 @@ class ConstraintButtonsPanel(Panel):
            row.operator("constraint.disable_keep_transform", text="", icon='CANCEL')

    @staticmethod
-    def space_template(layout, con, target=True, owner=True):
+    def space_template(layout, con, target=True, owner=True, separator=True):
        if target or owner:
-            layout.separator()
+            if separator:
+                layout.separator()
            if target:
                layout.prop(con, "target_space", text="Target")
            if owner:
                layout.prop(con, "owner_space", text="Owner")

+            if con.target_space == 'CUSTOM' or con.owner_space == 'CUSTOM':
+                col = layout.column()
+                col.prop(con, "space_object")
+                if con.space_object and con.space_object.type == 'ARMATURE':
+                    col.prop_search(con, "space_subtarget", con.space_object.data, "bones", text="Bone")
+                elif con.space_object and con.space_object.type in {'MESH', 'LATTICE'}:
+                    col.prop_search(con, "space_subtarget", con.space_object, "vertex_groups", text="Vertex Group")
+
    @staticmethod
    def target_template(layout, con, subtargets=True):
        col = layout.column()
@@ -237,7 +246,7 @@ class ConstraintButtonsPanel(Panel):
        row.label(icon="BLANK1")

        layout.prop(con, "use_transform_limit")
-        layout.prop(con, "owner_space")
+        self.space_template(layout, con, target=False, owner=True)

        self.draw_influence(layout, con)

@@ -306,7 +315,7 @@ class ConstraintButtonsPanel(Panel):
        row.prop_decorator(con, "max_z")

        layout.prop(con, "use_transform_limit")
-        layout.prop(con, "owner_space")
+        self.space_template(layout, con, target=False, owner=True)

        self.draw_influence(layout, con)

@@ -375,7 +384,7 @@ class ConstraintButtonsPanel(Panel):
        row.prop_decorator(con, "max_z")

        layout.prop(con, "use_transform_limit")
-        layout.prop(con, "owner_space")
+        self.space_template(layout, con, target=False, owner=True)

        self.draw_influence(layout, con)

@@ -483,7 +492,7 @@ class ConstraintButtonsPanel(Panel):

        layout.prop(con, "volume")

-        layout.prop(con, "owner_space")
+        self.space_template(layout, con, target=False, owner=True)

        self.draw_influence(layout, con)

@@ -1117,7 +1126,7 @@ class ConstraintButtonsSubPanel(Panel):
        col = layout.column()
        col.active = not con.use_eval_time
        col.prop(con, "transform_channel", text="Channel")
-        col.prop(con, "target_space")
+        ConstraintButtonsPanel.space_template(col, con, target=True, owner=False, separator=False)

        sub = col.column(align=True)
        sub.prop(con, "min", text="Range Min")
--- a/source/blender/blenkernel/BKE_constraint.h
+++ b/source/blender/blenkernel/BKE_constraint.h
@@ -56,6 +56,8 @@ typedef struct bConstraintOb {
  float matrix[4][4];
  /** original matrix (before constraint solving) */
  float startmat[4][4];
+  /** space matrix for custom object space */
+  float space_obj_world_matrix[4][4];

  /** type of owner  */
  short type;
@@ -203,11 +205,14 @@ void BKE_constraints_clear_evalob(struct bConstraintOb *cob);

 void BKE_constraint_mat_convertspace(struct Object *ob,
                                     struct bPoseChannel *pchan,
+                                     struct bConstraintOb *cob,
                                     float mat[4][4],
                                     short from,
                                     short to,
                                     const bool keep_scale);

+int BKE_constraint_targets_get(struct bConstraint *con, struct ListBase *list);
+void BKE_constraint_targets_flush(struct bConstraint *con, struct ListBase *list, bool no_copy);
 void BKE_constraint_target_matrix_get(struct Depsgraph *depsgraph,
                                      struct Scene *scene,
                                      struct bConstraint *con,
@@ -221,6 +226,7 @@ void BKE_constraint_targets_for_solving_get(struct Depsgraph *depsgraph,
                                            struct bConstraintOb *ob,
                                            struct ListBase *targets,
                                            float ctime);
+void BKE_constraint_custom_object_space_init(struct bConstraintOb *cob, struct bConstraint *con);
 void BKE_constraints_solve(struct Depsgraph *depsgraph,
                           struct ListBase *conlist,
                           struct bConstraintOb *cob,
--- a/source/blender/blenkernel/intern/action.c
+++ b/source/blender/blenkernel/intern/action.c
@@ -992,13 +992,10 @@ 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]) {
@@ -1010,9 +1007,7 @@ 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);
          }
        }

--- a/source/blender/blenkernel/intern/armature.c
+++ b/source/blender/blenkernel/intern/armature.c
@@ -2381,22 +2381,17 @@ static void pose_proxy_sync(Object *ob, Object *from, int layer_protected)

      /* constraints - set target ob pointer to own object */
      for (con = pchanw.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 == from) {
              ct->tar = ob;
            }
          }

-          if (cti->flush_constraint_targets) {
-            cti->flush_constraint_targets(con, &targets, 0);
-          }
+          BKE_constraint_targets_flush(con, &targets, 0);
        }
      }

--- a/source/blender/blenkernel/intern/constraint.c
+++ b/source/blender/blenkernel/intern/constraint.c
@@ -261,8 +261,13 @@ void BKE_constraints_clear_evalob(bConstraintOb *cob)
 * of a matrix from one space to another for constraint evaluation.
 * For now, this is only implemented for Objects and PoseChannels.
 */
-void BKE_constraint_mat_convertspace(
-    Object *ob, bPoseChannel *pchan, float mat[4][4], short from, short to, const bool keep_scale)
+void BKE_constraint_mat_convertspace(Object *ob,
+                                     bPoseChannel *pchan,
+                                     bConstraintOb *cob,
+                                     float mat[4][4],
+                                     short from,
+                                     short to,
+                                     const bool keep_scale)
 {
  float diff_mat[4][4];
  float imat[4][4];
@@ -282,25 +287,30 @@ void BKE_constraint_mat_convertspace(
    switch (from) {
      case CONSTRAINT_SPACE_WORLD: /* ---------- FROM WORLDSPACE ---------- */
      {
-        /* world to pose */
-        invert_m4_m4(imat, ob->obmat);
-        mul_m4_m4m4(mat, imat, mat);
+        if (to == CONSTRAINT_SPACE_CUSTOM) {
+          /* World to custom. */
+          BLI_assert(cob);
+          invert_m4_m4(imat, cob->space_obj_world_matrix);
+          mul_m4_m4m4(mat, imat, mat);
+        }
+        else {
+          /* World to pose. */
+          invert_m4_m4(imat, ob->obmat);
+          mul_m4_m4m4(mat, imat, mat);

-        /* use pose-space as stepping stone for other spaces... */
-        if (ELEM(to, CONSTRAINT_SPACE_LOCAL, CONSTRAINT_SPACE_PARLOCAL)) {
-          /* call self with slightly different values */
-          BKE_constraint_mat_convertspace(ob, pchan, mat, CONSTRAINT_SPACE_POSE, to, keep_scale);
+          /* Use pose-space as stepping stone for other spaces. */
+          if (ELEM(to, CONSTRAINT_SPACE_LOCAL, CONSTRAINT_SPACE_PARLOCAL)) {
+            /* Call self with slightly different values. */
+            BKE_constraint_mat_convertspace(
+                ob, pchan, cob, mat, CONSTRAINT_SPACE_POSE, to, keep_scale);
+          }
        }
        break;
      }
      case CONSTRAINT_SPACE_POSE: /* ---------- FROM POSESPACE ---------- */
      {
-        /* pose to world */
-        if (to == CONSTRAINT_SPACE_WORLD) {
-          mul_m4_m4m4(mat, ob->obmat, mat);
-        }
        /* pose to local */
-        else if (to == CONSTRAINT_SPACE_LOCAL) {
+        if (to == CONSTRAINT_SPACE_LOCAL) {
          if (pchan->bone) {
            BKE_armature_mat_pose_to_bone(pchan, mat, mat);
          }
@@ -312,6 +322,16 @@ void BKE_constraint_mat_convertspace(
            mul_m4_m4m4(mat, imat, mat);
          }
        }
+        else {
+          /* Pose to world. */
+          mul_m4_m4m4(mat, ob->obmat, mat);
+          /* Use world-space as stepping stone for other spaces. */
+          if (to != CONSTRAINT_SPACE_WORLD) {
+            /* Call self with slightly different values. */
+            BKE_constraint_mat_convertspace(
+                ob, pchan, cob, mat, CONSTRAINT_SPACE_WORLD, to, keep_scale);
+          }
+        }
        break;
      }
      case CONSTRAINT_SPACE_LOCAL: /* ------------ FROM LOCALSPACE --------- */
@@ -323,9 +343,10 @@ void BKE_constraint_mat_convertspace(
        }

        /* use pose-space as stepping stone for other spaces */
-        if (ELEM(to, CONSTRAINT_SPACE_WORLD, CONSTRAINT_SPACE_PARLOCAL)) {
+        if (ELEM(to, CONSTRAINT_SPACE_WORLD, CONSTRAINT_SPACE_PARLOCAL, CONSTRAINT_SPACE_CUSTOM)) {
          /* call self with slightly different values */
-          BKE_constraint_mat_convertspace(ob, pchan, mat, CONSTRAINT_SPACE_POSE, to, keep_scale);
+          BKE_constraint_mat_convertspace(
+              ob, pchan, cob, mat, CONSTRAINT_SPACE_POSE, to, keep_scale);
        }
        break;
      }
@@ -337,9 +358,24 @@ void BKE_constraint_mat_convertspace(
        }

        /* use pose-space as stepping stone for other spaces */
-        if (ELEM(to, CONSTRAINT_SPACE_WORLD, CONSTRAINT_SPACE_LOCAL)) {
+        if (ELEM(to, CONSTRAINT_SPACE_WORLD, CONSTRAINT_SPACE_LOCAL, CONSTRAINT_SPACE_CUSTOM)) {
          /* call self with slightly different values */
-          BKE_constraint_mat_convertspace(ob, pchan, mat, CONSTRAINT_SPACE_POSE, to, keep_scale);
+          BKE_constraint_mat_convertspace(
+              ob, pchan, cob, mat, CONSTRAINT_SPACE_POSE, to, keep_scale);
+        }
+        break;
+      }
+      case CONSTRAINT_SPACE_CUSTOM: /* -------------- FROM CUSTOM SPACE ---------- */
+      {
+        /* Custom to world. */
+        BLI_assert(cob);
+        mul_m4_m4m4(mat, cob->space_obj_world_matrix, mat);
+
+        /* Use world-space as stepping stone for other spaces. */
+        if (to != CONSTRAINT_SPACE_WORLD) {
+          /* Call self with slightly different values. */
+          BKE_constraint_mat_convertspace(
+              ob, pchan, cob, mat, CONSTRAINT_SPACE_WORLD, to, keep_scale);
        }
        break;
      }
@@ -347,37 +383,44 @@ void BKE_constraint_mat_convertspace(
  }
  else {
    /* objects */
-    if (from == CONSTRAINT_SPACE_WORLD && to == CONSTRAINT_SPACE_LOCAL) {
-      /* check if object has a parent */
-      if (ob->parent) {
-        /* 'subtract' parent's effects from owner */
-        mul_m4_m4m4(diff_mat, ob->parent->obmat, ob->parentinv);
-        invert_m4_m4_safe(imat, diff_mat);
-        mul_m4_m4m4(mat, imat, mat);
-      }
-      else {
-        /* Local space in this case will have to be defined as local to the owner's
-         * transform-property-rotated axes. So subtract this rotation component.
-         */
-        /* XXX This is actually an ugly hack, local space of a parent-less object *is* the same as
-         *     global space!
-         *     Think what we want actually here is some kind of 'Final Space', i.e
-         *     . once transformations are applied - users are often confused about this too,
-         *     this is not consistent with bones
-         *     local space either... Meh :|
-         *     --mont29
-         */
-        BKE_object_to_mat4(ob, diff_mat);
-        if (!keep_scale) {
-          normalize_m4(diff_mat);
+    if (from == CONSTRAINT_SPACE_WORLD) {
+      if (to == CONSTRAINT_SPACE_LOCAL) {
+        /* Check if object has a parent. */
+        if (ob->parent) {
+          /* 'subtract' parent's effects from owner. */
+          mul_m4_m4m4(diff_mat, ob->parent->obmat, ob->parentinv);
+          invert_m4_m4_safe(imat, diff_mat);
+          mul_m4_m4m4(mat, imat, mat);
        }
-        zero_v3(diff_mat[3]);
+        else {
+          /* Local space in this case will have to be defined as local to the owner's
+           * transform-property-rotated axes. So subtract this rotation component.
+           */
+          /* XXX This is actually an ugly hack, local space of a parent-less object *is* the same
+           * as global space! Think what we want actually here is some kind of 'Final Space', i.e
+           *     . once transformations are applied - users are often confused about this too,
+           *     this is not consistent with bones
+           *     local space either... Meh :|
+           *     --mont29
+           */
+          BKE_object_to_mat4(ob, diff_mat);
+          if (!keep_scale) {
+            normalize_m4(diff_mat);
+          }
+          zero_v3(diff_mat[3]);

-        invert_m4_m4_safe(imat, diff_mat);
+          invert_m4_m4_safe(imat, diff_mat);
+          mul_m4_m4m4(mat, imat, mat);
+        }
+      }
+      else if (to == CONSTRAINT_SPACE_CUSTOM) {
+        /* 'subtract' custom objects's effects from owner. */
+        BLI_assert(cob);
+        invert_m4_m4_safe(imat, cob->space_obj_world_matrix);
        mul_m4_m4m4(mat, imat, mat);
      }
    }
-    else if (from == CONSTRAINT_SPACE_LOCAL && to == CONSTRAINT_SPACE_WORLD) {
+    else if (from == CONSTRAINT_SPACE_LOCAL) {
      /* check that object has a parent - otherwise this won't work */
      if (ob->parent) {
        /* 'add' parent's effect back to owner */
@@ -397,6 +440,24 @@ void BKE_constraint_mat_convertspace(

        mul_m4_m4m4(mat, diff_mat, mat);
      }
+      if (to == CONSTRAINT_SPACE_CUSTOM) {
+        /* 'subtract' objects's effects from owner. */
+        BLI_assert(cob);
+        invert_m4_m4_safe(imat, cob->space_obj_world_matrix);
+        mul_m4_m4m4(mat, imat, mat);
+      }
+    }
+    else if (from == CONSTRAINT_SPACE_CUSTOM) {
+      /* Custom to world. */
+      BLI_assert(cob);
+      mul_m4_m4m4(mat, cob->space_obj_world_matrix, mat);
+
+      /* Use world-space as stepping stone for other spaces. */
+      if (to != CONSTRAINT_SPACE_WORLD) {
+        /* Call self with slightly different values. */
+        BKE_constraint_mat_convertspace(
+            ob, pchan, cob, mat, CONSTRAINT_SPACE_WORLD, to, keep_scale);
+      }
    }
  }
 }
@@ -573,6 +634,7 @@ static void contarget_get_lattice_mat(Object *ob, const char *substring, float m
 /* The cases where the target can be object data have not been implemented */
 static void constraint_target_to_mat4(Object *ob,
                                      const char *substring,
+                                      bConstraintOb *cob,
                                      float mat[4][4],
                                      short from,
                                      short to,
@@ -582,7 +644,7 @@ static void constraint_target_to_mat4(Object *ob,
  /* Case OBJECT */
  if (substring[0] == '\0') {
    copy_m4_m4(mat, ob->obmat);
-    BKE_constraint_mat_convertspace(ob, NULL, mat, from, to, false);
+    BKE_constraint_mat_convertspace(ob, NULL, cob, mat, from, to, false);
  }
  /* Case VERTEXGROUP */
  /* Current method just takes the average location of all the points in the
@@ -595,11 +657,11 @@ static void constraint_target_to_mat4(Object *ob,
   */
  else if (ob->type == OB_MESH) {
    contarget_get_mesh_mat(ob, substring, mat);
-    BKE_constraint_mat_convertspace(ob, NULL, mat, from, to, false);
+    BKE_constraint_mat_convertspace(ob, NULL, cob, mat, from, to, false);
  }
  else if (ob->type == OB_LATTICE) {
    contarget_get_lattice_mat(ob, substring, mat);
-    BKE_constraint_mat_convertspace(ob, NULL, mat, from, to, false);
+    BKE_constraint_mat_convertspace(ob, NULL, cob, mat, from, to, false);
  }
  /* Case BONE */
  else {
@@ -662,7 +724,7 @@ static void constraint_target_to_mat4(Object *ob,
    }

    /* convert matrix space as required */
-    BKE_constraint_mat_convertspace(ob, pchan, mat, from, to, false);
+    BKE_constraint_mat_convertspace(ob, pchan, cob, mat, from, to, false);
  }
 }

@@ -705,13 +767,14 @@ static bConstraintTypeInfo CTI_CONSTRNAME = {
 */
 static void default_get_tarmat(struct Depsgraph *UNUSED(depsgraph),
                               bConstraint *con,
-                               bConstraintOb *UNUSED(cob),
+                               bConstraintOb *cob,
                               bConstraintTarget *ct,
                               float UNUSED(ctime))
 {
  if (VALID_CONS_TARGET(ct)) {
    constraint_target_to_mat4(ct->tar,
                              ct->subtarget,
+                              cob,
                              ct->matrix,
                              CONSTRAINT_SPACE_WORLD,
                              ct->space,
@@ -727,13 +790,14 @@ static void default_get_tarmat(struct Depsgraph *UNUSED(depsgraph),
 */
 static void default_get_tarmat_full_bbone(struct Depsgraph *UNUSED(depsgraph),
                                          bConstraint *con,
-                                          bConstraintOb *UNUSED(cob),
+                                          bConstraintOb *cob,
                                          bConstraintTarget *ct,
                                          float UNUSED(ctime))
 {
  if (VALID_CONS_TARGET(ct)) {
    constraint_target_to_mat4(ct->tar,
                              ct->subtarget,
+                              cob,
                              ct->matrix,
                              CONSTRAINT_SPACE_WORLD,
                              ct->space,
@@ -844,6 +908,11 @@ static void default_get_tarmat_full_bbone(struct Depsgraph *UNUSED(depsgraph),
  } \
  (void)0

+static bool is_custom_space_needed(bConstraint *con)
+{
+  return con->ownspace == CONSTRAINT_SPACE_CUSTOM || con->tarspace == CONSTRAINT_SPACE_CUSTOM;
+}
+
 /* --------- ChildOf Constraint ------------ */

 static void childof_new_data(void *cdata)
@@ -1262,6 +1331,7 @@ static void kinematic_get_tarmat(struct Depsgraph *UNUSED(depsgraph),
  if (VALID_CONS_TARGET(ct)) {
    constraint_target_to_mat4(ct->tar,
                              ct->subtarget,
+                              cob,
                              ct->matrix,
                              CONSTRAINT_SPACE_WORLD,
                              ct->space,
@@ -2276,7 +2346,7 @@ static void pycon_id_looper(bConstraint *con, ConstraintIDFunc func, void *userd
 /* Whether this approach is maintained remains to be seen (aligorith) */
 static void pycon_get_tarmat(struct Depsgraph *UNUSED(depsgraph),
                             bConstraint *con,
-                             bConstraintOb *UNUSED(cob),
+                             bConstraintOb *cob,
                             bConstraintTarget *ct,
                             float UNUSED(ctime))
 {
@@ -2295,6 +2365,7 @@ static void pycon_get_tarmat(struct Depsgraph *UNUSED(depsgraph),
     */
    constraint_target_to_mat4(ct->tar,
                              ct->subtarget,
+                              cob,
                              ct->matrix,
                              CONSTRAINT_SPACE_WORLD,
                              ct->space,
@@ -2654,6 +2725,7 @@ static void actcon_get_tarmat(struct Depsgraph *depsgraph,
      /* get the transform matrix of the target */
      constraint_target_to_mat4(ct->tar,
                                ct->subtarget,
+                                cob,
                                tempmat,
                                CONSTRAINT_SPACE_WORLD,
                                ct->space,
@@ -4116,7 +4188,7 @@ static void shrinkwrap_get_tarmat(struct Depsgraph *UNUSED(depsgraph),
           * See T42447. */
          unit_m4(mat);
          BKE_constraint_mat_convertspace(
-              cob->ob, cob->pchan, mat, CONSTRAINT_SPACE_LOCAL, scon->projAxisSpace, true);
+              cob->ob, cob->pchan, cob, mat, CONSTRAINT_SPACE_LOCAL, scon->projAxisSpace, true);
          invert_m4(mat);
          mul_mat3_m4_v3(mat, no);

@@ -5333,6 +5405,19 @@ static void con_unlink_refs_cb(bConstraint *UNUSED(con),
  }
 }

+/** Helper function to invoke the id_looper callback, including custom space. */
+static void con_invoke_id_looper(const bConstraintTypeInfo *cti,
+                                 bConstraint *con,
+                                 ConstraintIDFunc func,
+                                 void *userdata)
+{
+  if (cti->id_looper) {
+    cti->id_looper(con, func, userdata);
+  }
+
+  func(con, (ID **)&con->space_object, false, userdata);
+}
+
 /**
 * Free data of a specific constraint if it has any info.
 * be sure to run #BIK_clear_data() when freeing an IK constraint,
@@ -5350,8 +5435,8 @@ void BKE_constraint_free_data_ex(bConstraint *con, bool do_id_user)
      }

      /* unlink the referenced resources it uses */
-      if (do_id_user && cti->id_looper) {
-        cti->id_looper(con, con_unlink_refs_cb, NULL);
+      if (do_id_user) {
+        con_invoke_id_looper(cti, con, con_unlink_refs_cb, NULL);
      }
    }

@@ -5518,9 +5603,12 @@ static bConstraint *add_new_constraint(Object *ob,
  return con;
 }

-bool BKE_constraint_target_uses_bbone(struct bConstraint *con,
-                                      struct bConstraintTarget *UNUSED(ct))
+bool BKE_constraint_target_uses_bbone(struct bConstraint *con, struct bConstraintTarget *ct)
 {
+  if (ct->flag & CONSTRAINT_TAR_CUSTOM_SPACE) {
+    return false;
+  }
+
  return (con->flag & CONSTRAINT_BBONE_SHAPE) || (con->type == CONSTRAINT_TYPE_ARMATURE);
 }

@@ -5554,9 +5642,7 @@ void BKE_constraints_id_loop(ListBase *conlist, ConstraintIDFunc func, void *use
    const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);

    if (cti) {
-      if (cti->id_looper) {
-        cti->id_looper(con, func, userdata);
-      }
+      con_invoke_id_looper(cti, con, func, userdata);
    }
  }
 }
@@ -5608,16 +5694,14 @@ static void constraint_copy_data_ex(bConstraint *dst,
    }

    /* Fix usercounts for all referenced data that need it. */
-    if (cti->id_looper && (flag & LIB_ID_CREATE_NO_USER_REFCOUNT) == 0) {
-      cti->id_looper(dst, con_fix_copied_refs_cb, NULL);
+    if ((flag & LIB_ID_CREATE_NO_USER_REFCOUNT) == 0) {
+      con_invoke_id_looper(cti, dst, con_fix_copied_refs_cb, NULL);
    }

    /* for proxies we don't want to make extern */
    if (do_extern) {
      /* go over used ID-links for this constraint to ensure that they are valid for proxies */
-      if (cti->id_looper) {
-        cti->id_looper(dst, con_extern_cb, NULL);
-      }
+      con_invoke_id_looper(cti, dst, con_extern_cb, NULL);
    }
  }
 }
@@ -5872,6 +5956,61 @@ bool BKE_constraints_proxylocked_owner(Object *ob, bPoseChannel *pchan)

 /* -------- Target-Matrix Stuff ------- */

+/** 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. */
+int BKE_constraint_targets_get(struct bConstraint *con, struct ListBase *list)
+{
+  int count = 0;
+
+  if (con && list) {
+    const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
+
+    if (cti) {
+      if (cti->get_constraint_targets) {
+        count = cti->get_constraint_targets(con, list);
+      }
+
+      /* Add the custom target. */
+      if (is_custom_space_needed(con)) {
+        bConstraintTarget *ct;
+        SINGLETARGET_GET_TARS(con, con->space_object, con->space_subtarget, ct, list);
+        ct->space = CONSTRAINT_SPACE_WORLD;
+        ct->flag |= CONSTRAINT_TAR_CUSTOM_SPACE;
+        count++;
+      }
+    }
+  }
+
+  return count;
+}
+
+/** Copies data from the list produced by BKE_constraint_targets_get back and frees memory. */
+void BKE_constraint_targets_flush(struct bConstraint *con, struct ListBase *list, bool no_copy)
+{
+  if (con && list) {
+    const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
+
+    if (cti) {
+      /* Remove the custom target. */
+      if (is_custom_space_needed(con)) {
+        bConstraintTarget *ct = (bConstraintTarget *)list->last;
+        BLI_assert(ct && (ct->flag & CONSTRAINT_TAR_CUSTOM_SPACE));
+
+        if (!no_copy) {
+          con->space_object = ct->tar;
+          BLI_strncpy(con->space_subtarget, ct->subtarget, sizeof(con->space_subtarget));
+        }
+
+        BLI_freelinkN(list, ct);
+      }
+
+      if (cti->flush_constraint_targets) {
+        cti->flush_constraint_targets(con, list, no_copy);
+      }
+    }
+  }
+}
+
 /* This function is a relic from the prior implementations of the constraints system, when all
 * constraints either had one or no targets. It used to be called during the main constraint
 * solving loop, but is now only used for the remaining cases for a few constraints.
@@ -5930,6 +6069,9 @@ void BKE_constraint_target_matrix_get(struct Depsgraph *depsgraph,
      }
    }

+    /* Initialize the custom space for use in calculating the matrices. */
+    BKE_constraint_custom_object_space_init(cob, con);
+
    /* get targets - we only need the first one though (and there should only be one) */
    cti->get_constraint_targets(con, &targets);

@@ -5994,6 +6136,26 @@ void BKE_constraint_targets_for_solving_get(struct Depsgraph *depsgraph,
  }
 }

+/** Initialize the Custom Space matrix inside cob. */
+void BKE_constraint_custom_object_space_init(bConstraintOb *cob, bConstraint *con)
+{
+  if (con && con->space_object && is_custom_space_needed(con)) {
+    /* Basically default_get_tarmat but without the unused parameters. */
+    constraint_target_to_mat4(con->space_object,
+                              con->space_subtarget,
+                              NULL,
+                              cob->space_obj_world_matrix,
+                              CONSTRAINT_SPACE_WORLD,
+                              CONSTRAINT_SPACE_WORLD,
+                              0,
+                              0);
+
+    return;
+  }
+
+  unit_m4(cob->space_obj_world_matrix);
+}
+
 /* ---------- Evaluation ----------- */

 /* This function is called whenever constraints need to be evaluated. Currently, all
@@ -6042,12 +6204,15 @@ void BKE_constraints_solve(struct Depsgraph *depsgraph,
     */
    enf = con->enforce;

+    /* Initialize the custom space for use in calculating the matrices. */
+    BKE_constraint_custom_object_space_init(cob, con);
+
    /* make copy of world-space matrix pre-constraint for use with blending later */
    copy_m4_m4(oldmat, cob->matrix);

    /* move owner matrix into right space */
    BKE_constraint_mat_convertspace(
-        cob->ob, cob->pchan, cob->matrix, CONSTRAINT_SPACE_WORLD, con->ownspace, false);
+        cob->ob, cob->pchan, cob, cob->matrix, CONSTRAINT_SPACE_WORLD, con->ownspace, false);

    /* prepare targets for constraint solving */
    BKE_constraint_targets_for_solving_get(depsgraph, con, cob, &targets, ctime);
@@ -6066,7 +6231,7 @@ void BKE_constraints_solve(struct Depsgraph *depsgraph,
    /* move owner back into world-space for next constraint/other business */
    if ((con->flag & CONSTRAINT_SPACEONCE) == 0) {
      BKE_constraint_mat_convertspace(
-          cob->ob, cob->pchan, cob->matrix, con->ownspace, CONSTRAINT_SPACE_WORLD, false);
+          cob->ob, cob->pchan, cob, cob->matrix, con->ownspace, CONSTRAINT_SPACE_WORLD, false);
    }

    /* Interpolate the enforcement, to blend result of constraint into final owner transform
--- a/source/blender/blenkernel/intern/fcurve_driver.c
+++ b/source/blender/blenkernel/intern/fcurve_driver.c
@@ -411,7 +411,7 @@ static float dvar_eval_locDiff(ChannelDriver *driver, DriverVar *dvar)
          /* Extract transform just like how the constraints do it! */
          copy_m4_m4(mat, pchan->pose_mat);
          BKE_constraint_mat_convertspace(
-              ob, pchan, mat, CONSTRAINT_SPACE_POSE, CONSTRAINT_SPACE_LOCAL, false);
+              ob, pchan, NULL, mat, CONSTRAINT_SPACE_POSE, CONSTRAINT_SPACE_LOCAL, false);

          /* ... and from that, we get our transform. */
          copy_v3_v3(tmp_loc, mat[3]);
@@ -437,7 +437,7 @@ static float dvar_eval_locDiff(ChannelDriver *driver, DriverVar *dvar)
          /* Extract transform just like how the constraints do it! */
          copy_m4_m4(mat, ob->obmat);
          BKE_constraint_mat_convertspace(
-              ob, NULL, mat, CONSTRAINT_SPACE_WORLD, CONSTRAINT_SPACE_LOCAL, false);
+              ob, NULL, NULL, mat, CONSTRAINT_SPACE_WORLD, CONSTRAINT_SPACE_LOCAL, false);

          /* ... and from that, we get our transform. */
          copy_v3_v3(tmp_loc, mat[3]);
@@ -514,7 +514,7 @@ static float dvar_eval_transChan(ChannelDriver *driver, DriverVar *dvar)
        /* Just like how the constraints do it! */
        copy_m4_m4(mat, pchan->pose_mat);
        BKE_constraint_mat_convertspace(
-            ob, pchan, mat, CONSTRAINT_SPACE_POSE, CONSTRAINT_SPACE_LOCAL, false);
+            ob, pchan, NULL, mat, CONSTRAINT_SPACE_POSE, CONSTRAINT_SPACE_LOCAL, false);
      }
      else {
        /* Specially calculate local matrix, since chan_mat is not valid
@@ -541,7 +541,7 @@ static float dvar_eval_transChan(ChannelDriver *driver, DriverVar *dvar)
        /* Just like how the constraints do it! */
        copy_m4_m4(mat, ob->obmat);
        BKE_constraint_mat_convertspace(
-            ob, NULL, mat, CONSTRAINT_SPACE_WORLD, CONSTRAINT_SPACE_LOCAL, false);
+            ob, NULL, NULL, mat, CONSTRAINT_SPACE_WORLD, CONSTRAINT_SPACE_LOCAL, false);
      }
      else {
        /* Transforms to matrix. */
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -2242,22 +2242,17 @@ 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. */
    for (con = chan->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) {
            ct->tar = obn;
          }
        }

-        if (cti->flush_constraint_targets) {
-          cti->flush_constraint_targets(con, &targets, 0);
-        }
+        BKE_constraint_targets_flush(con, &targets, 0);
      }
    }
  }
@@ -5337,12 +5332,10 @@ bool BKE_object_modifier_update_subframe(Depsgraph *depsgraph,

    /* also update constraint targets */
    for (con = ob->constraints.first; con; con = con->next) {
-      const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
      ListBase targets = {NULL, NULL};

-      if (cti && cti->get_constraint_targets) {
+      if (BKE_constraint_targets_get(con, &targets)) {
        bConstraintTarget *ct;
-        cti->get_constraint_targets(con, &targets);
        for (ct = targets.first; ct; ct = ct->next) {
          if (ct->tar) {
            BKE_object_modifier_update_subframe(
@@ -5350,9 +5343,7 @@ bool BKE_object_modifier_update_subframe(Depsgraph *depsgraph,
          }
        }
        /* free temp targets */
-        if (cti->flush_constraint_targets) {
-          cti->flush_constraint_targets(con, &targets, 0);
-        }
+        BKE_constraint_targets_flush(con, &targets, 0);
      }
    }
  }
--- a/source/blender/depsgraph/intern/builder/deg_builder_relations.cc
+++ b/source/blender/depsgraph/intern/builder/deg_builder_relations.cc
@@ -1072,6 +1072,7 @@ void DepsgraphRelationBuilder::build_constraints(ID *id,
  /* Add dependencies for each constraint in turn. */
  for (bConstraint *con = (bConstraint *)constraints->first; con; con = con->next) {
    const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
+    ListBase targets = {nullptr, nullptr};
    /* Invalid constraint type. */
    if (cti == nullptr) {
      continue;
@@ -1120,9 +1121,7 @@ void DepsgraphRelationBuilder::build_constraints(ID *id,
        add_relation(cache_key, constraint_op_key, cti->name);
      }
    }
-    else if (cti->get_constraint_targets) {
-      ListBase targets = {nullptr, nullptr};
-      cti->get_constraint_targets(con, &targets);
+    else if (BKE_constraint_targets_get(con, &targets)) {
      LISTBASE_FOREACH (bConstraintTarget *, ct, &targets) {
        if (ct->tar == nullptr) {
          continue;
@@ -1232,9 +1231,7 @@ void DepsgraphRelationBuilder::build_constraints(ID *id,
          add_relation(target_transform_key, constraint_op_key, cti->name);
        }
      }
-      if (cti->flush_constraint_targets) {
-        cti->flush_constraint_targets(con, &targets, true);
-      }
+      BKE_constraint_targets_flush(con, &targets, true);
    }
  }
 }
--- a/source/blender/draw/engines/overlay/overlay_extra.c
+++ b/source/blender/draw/engines/overlay/overlay_extra.c
@@ -1335,16 +1335,19 @@ static void OVERLAY_relationship_lines(OVERLAY_ExtraCallBuffers *cb,
      }
      else {
        const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(curcon);
+        ListBase targets = {NULL, NULL};

-        if ((cti && cti->get_constraint_targets) && (curcon->ui_expand_flag & (1 << 0))) {
-          ListBase targets = {NULL, NULL};
+        if ((curcon->ui_expand_flag & (1 << 0)) && BKE_constraint_targets_get(curcon, &targets)) {
          bConstraintTarget *ct;

-          cti->get_constraint_targets(curcon, &targets);
+          BKE_constraint_custom_object_space_init(cob, curcon);

          for (ct = targets.first; ct; ct = ct->next) {
            /* calculate target's matrix */
-            if (cti->get_target_matrix) {
+            if (ct->flag & CONSTRAINT_TAR_CUSTOM_SPACE) {
+              copy_m4_m4(ct->matrix, cob->space_obj_world_matrix);
+            }
+            else if (cti->get_target_matrix) {
              cti->get_target_matrix(depsgraph, curcon, cob, ct, DEG_get_ctime(depsgraph));
            }
            else {
@@ -1353,9 +1356,7 @@ static void OVERLAY_relationship_lines(OVERLAY_ExtraCallBuffers *cb,
            OVERLAY_extra_line_dashed(cb, ct->matrix[3], ob->obmat[3], constraint_color);
          }

-          if (cti->flush_constraint_targets) {
-            cti->flush_constraint_targets(curcon, &targets, 1);
-          }
+          BKE_constraint_targets_flush(curcon, &targets, 1);
        }
      }
    }
--- a/source/blender/editors/armature/armature_add.c
+++ b/source/blender/editors/armature/armature_add.c
@@ -400,13 +400,10 @@ static void updateDuplicateSubtarget(EditBone *dup_bone,
        /* does this constraint have a subtarget in
         * this armature?
         */
-        const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(curcon);
        ListBase targets = {NULL, NULL};
        bConstraintTarget *ct;

-        if (cti && cti->get_constraint_targets) {
-          cti->get_constraint_targets(curcon, &targets);
-
+        if (BKE_constraint_targets_get(curcon, &targets)) {
          for (ct = targets.first; ct; ct = ct->next) {
            if ((ct->tar == ob) && (ct->subtarget[0])) {
              oldtarget = get_named_editbone(editbones, ct->subtarget);
@@ -434,9 +431,7 @@ static void updateDuplicateSubtarget(EditBone *dup_bone,
            }
          }

-          if (cti->flush_constraint_targets) {
-            cti->flush_constraint_targets(curcon, &targets, 0);
-          }
+          BKE_constraint_targets_flush(curcon, &targets, 0);
        }
      }
    }
@@ -453,10 +448,13 @@ static void updateDuplicateActionConstraintSettings(EditBone *dup_bone,

  float mat[4][4];

+  bConstraintOb cob = {.depsgraph = NULL, .scene = NULL, .ob = ob, .pchan = NULL};
+  BKE_constraint_custom_object_space_init(&cob, curcon);
+
  unit_m4(mat);
  bPoseChannel *target_pchan = BKE_pose_channel_find_name(ob->pose, act_con->subtarget);
  BKE_constraint_mat_convertspace(
-      ob, target_pchan, mat, curcon->tarspace, CONSTRAINT_SPACE_LOCAL, false);
+      ob, target_pchan, &cob, mat, curcon->tarspace, CONSTRAINT_SPACE_LOCAL, false);

  float max_axis_val = 0;
  int max_axis = 0;
@@ -605,8 +603,11 @@ static void updateDuplicateLocRotConstraintSettings(Object *ob,

  unit_m4(local_mat);

+  bConstraintOb cob = {.depsgraph = NULL, .scene = NULL, .ob = ob, .pchan = pchan};
+  BKE_constraint_custom_object_space_init(&cob, curcon);
+
  BKE_constraint_mat_convertspace(
-      ob, pchan, local_mat, curcon->ownspace, CONSTRAINT_SPACE_LOCAL, false);
+      ob, pchan, &cob, local_mat, curcon->ownspace, CONSTRAINT_SPACE_LOCAL, false);

  if (curcon->type == CONSTRAINT_TYPE_ROTLIMIT) {
    /* Zero out any location translation */
@@ -657,9 +658,12 @@ static void updateDuplicateTransformConstraintSettings(Object *ob,

  float target_mat[4][4], own_mat[4][4], imat[4][4];

+  bConstraintOb cob = {.depsgraph = NULL, .scene = NULL, .ob = ob, .pchan = pchan};
+  BKE_constraint_custom_object_space_init(&cob, curcon);
+
  unit_m4(own_mat);
  BKE_constraint_mat_convertspace(
-      ob, pchan, own_mat, curcon->ownspace, CONSTRAINT_SPACE_LOCAL, false);
+      ob, pchan, &cob, own_mat, curcon->ownspace, CONSTRAINT_SPACE_LOCAL, false);

  /* ###Source map mirroring### */
  float old_min, old_max;
@@ -717,7 +721,7 @@ static void updateDuplicateTransformConstraintSettings(Object *ob,
  bPoseChannel *target_pchan = BKE_pose_channel_find_name(ob->pose, trans->subtarget);
  unit_m4(target_mat);
  BKE_constraint_mat_convertspace(
-      ob, target_pchan, target_mat, curcon->tarspace, CONSTRAINT_SPACE_LOCAL, false);
+      ob, target_pchan, &cob, target_mat, curcon->tarspace, CONSTRAINT_SPACE_LOCAL, false);

  invert_m4_m4(imat, target_mat);
  /* convert values into local object space */
--- a/source/blender/editors/armature/armature_naming.c
+++ b/source/blender/editors/armature/armature_naming.c
@@ -126,13 +126,10 @@ static void constraint_bone_name_fix(Object *ob,
  bConstraintTarget *ct;

  for (curcon = conlist->first; curcon; curcon = curcon->next) {
-    const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(curcon);
    ListBase targets = {NULL, NULL};

    /* constraint targets */
-    if (cti && cti->get_constraint_targets) {
-      cti->get_constraint_targets(curcon, &targets);
-
+    if (BKE_constraint_targets_get(curcon, &targets)) {
      for (ct = targets.first; ct; ct = ct->next) {
        if (ct->tar == ob) {
          if (STREQ(ct->subtarget, oldname)) {
@@ -141,9 +138,7 @@ static void constraint_bone_name_fix(Object *ob,
        }
      }

-      if (cti->flush_constraint_targets) {
-        cti->flush_constraint_targets(curcon, &targets, 0);
-      }
+      BKE_constraint_targets_flush(curcon, &targets, 0);
    }

    /* action constraints */
--- a/source/blender/editors/armature/armature_relations.c
+++ b/source/blender/editors/armature/armature_relations.c
@@ -84,14 +84,11 @@ static void joined_armature_fix_links_constraints(Main *bmain,
  bool changed = false;

  for (con = lb->first; con; con = con->next) {
-    const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
    ListBase targets = {NULL, NULL};
    bConstraintTarget *ct;

    /* constraint targets */
-    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 == srcArm) {
          if (ct->subtarget[0] == '\0') {
@@ -106,9 +103,7 @@ static void joined_armature_fix_links_constraints(Main *bmain,
        }
      }

-      if (cti->flush_constraint_targets) {
-        cti->flush_constraint_targets(con, &targets, 0);
-      }
+      BKE_constraint_targets_flush(con, &targets, 0);
    }

    /* action constraint? (pose constraints only) */
@@ -467,14 +462,11 @@ static void separated_armature_fix_links(Main *bmain, Object *origArm, Object *n
    if (ob->type == OB_ARMATURE) {
      for (pchan = ob->pose->chanbase.first; pchan; pchan = pchan->next) {
        for (con = pchan->constraints.first; con; con = con->next) {
-          const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
          ListBase targets = {NULL, NULL};
          bConstraintTarget *ct;

          /* constraint targets */
-          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) {
              /* Any targets which point to original armature
               * are redirected to the new one only if:
@@ -495,9 +487,7 @@ static void separated_armature_fix_links(Main *bmain, Object *origArm, Object *n
              }
            }

-            if (cti->flush_constraint_targets) {
-              cti->flush_constraint_targets(con, &targets, 0);
-            }
+            BKE_constraint_targets_flush(con, &targets, 0);
          }
        }
      }
@@ -506,14 +496,11 @@ static void separated_armature_fix_links(Main *bmain, Object *origArm, Object *n
    /* fix object-level constraints */
    if (ob != origArm) {
      for (con = ob->constraints.first; con; con = con->next) {
-        const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
        ListBase targets = {NULL, NULL};
        bConstraintTarget *ct;

        /* constraint targets */
-        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) {
            /* any targets which point to original armature are redirected to the new one only if:
             * - the target isn't origArm/newArm itself
@@ -533,9 +520,7 @@ static void separated_armature_fix_links(Main *bmain, Object *origArm, Object *n
            }
          }

-          if (cti->flush_constraint_targets) {
-            cti->flush_constraint_targets(con, &targets, 0);
-          }
+          BKE_constraint_targets_flush(con, &targets, 0);
        }
      }
    }
--- a/source/blender/editors/armature/pose_select.c
+++ b/source/blender/editors/armature/pose_select.c
@@ -673,13 +673,10 @@ static int pose_select_constraint_target_exec(bContext *C, wmOperator *UNUSED(op
  CTX_DATA_BEGIN (C, bPoseChannel *, pchan, visible_pose_bones) {
    if (pchan->bone->flag & BONE_SELECTED) {
      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) {
            Object *ob = ct->tar;

@@ -695,9 +692,7 @@ static int pose_select_constraint_target_exec(bContext *C, wmOperator *UNUSED(op
            }
          }

-          if (cti->flush_constraint_targets) {
-            cti->flush_constraint_targets(con, &targets, 1);
-          }
+          BKE_constraint_targets_flush(con, &targets, 1);
        }
      }
    }
--- a/source/blender/editors/object/object_constraint.c
+++ b/source/blender/editors/object/object_constraint.c
@@ -271,13 +271,11 @@ static void set_constraint_nth_target(bConstraint *con,
                                      const char subtarget[],
                                      int index)
 {
-  const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
  ListBase targets = {NULL, NULL};
  bConstraintTarget *ct;
  int num_targets, i;

-  if (cti && cti->get_constraint_targets) {
-    cti->get_constraint_targets(con, &targets);
+  if (BKE_constraint_targets_get(con, &targets)) {
    num_targets = BLI_listbase_count(&targets);

    if (index < 0) {
@@ -300,9 +298,7 @@ static void set_constraint_nth_target(bConstraint *con,
      }
    }

-    if (cti->flush_constraint_targets) {
-      cti->flush_constraint_targets(con, &targets, 0);
-    }
+    BKE_constraint_targets_flush(con, &targets, 0);
  }
 }

@@ -315,7 +311,6 @@ static void set_constraint_nth_target(bConstraint *con,
 static void test_constraint(
    Main *bmain, Object *owner, bPoseChannel *pchan, bConstraint *con, int type)
 {
-  const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
  ListBase targets = {NULL, NULL};
  bConstraintTarget *ct;
  bool check_targets = true;
@@ -494,14 +489,7 @@ static void test_constraint(
  }

  /* Check targets for constraints */
-  if (check_targets && cti && cti->get_constraint_targets) {
-    cti->get_constraint_targets(con, &targets);
-
-    /* constraints with empty target list that actually require targets */
-    if (!targets.first && ELEM(con->type, CONSTRAINT_TYPE_ARMATURE)) {
-      con->flag |= CONSTRAINT_DISABLE;
-    }
-
+  if (check_targets && BKE_constraint_targets_get(con, &targets)) {
    /* disable and clear constraints targets that are incorrect */
    for (ct = targets.first; ct; ct = ct->next) {
      /* general validity checks (for those constraints that need this) */
@@ -572,8 +560,12 @@ static void test_constraint(
    }

    /* free any temporary targets */
-    if (cti->flush_constraint_targets) {
-      cti->flush_constraint_targets(con, &targets, 0);
+    BKE_constraint_targets_flush(con, &targets, 0);
+  }
+  else if (check_targets) {
+    /* constraints with empty target list that actually require targets */
+    if (ELEM(con->type, CONSTRAINT_TYPE_ARMATURE)) {
+      con->flag |= CONSTRAINT_DISABLE;
    }
  }
 }
--- a/source/blender/io/collada/BCAnimationSampler.cpp
+++ b/source/blender/io/collada/BCAnimationSampler.cpp
@@ -239,24 +239,26 @@ bool BCAnimationSampler::is_animated_by_constraint(Object *ob,
  for (con = (bConstraint *)conlist->first; con; con = con->next) {
    ListBase targets = {nullptr, nullptr};

-    const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
-
    if (!bc_validateConstraints(con)) {
      continue;
    }

-    if (cti && cti->get_constraint_targets) {
+    if (BKE_constraint_targets_get(con, &targets)) {
      bConstraintTarget *ct;
      Object *obtar;
-      cti->get_constraint_targets(con, &targets);
+      bool found = false;
+
      for (ct = (bConstraintTarget *)targets.first; ct; ct = ct->next) {
        obtar = ct->tar;
        if (obtar) {
          if (animated_objects.find(obtar) != animated_objects.end()) {
-            return true;
+            found = true;
+            break;
          }
        }
      }
+      BKE_constraint_targets_flush(con, &targets, true);
+      return found;
    }
  }
  return false;
--- a/source/blender/io/collada/SceneExporter.cpp
+++ b/source/blender/io/collada/SceneExporter.cpp
@@ -206,24 +206,19 @@ void SceneExporter::writeNode(Object *ob)
          /* not ideal: add the target object name as another parameter.
           * No real mapping in the .dae
           * Need support for multiple target objects also. */
-          const bConstraintTypeInfo *cti = BKE_constraint_typeinfo_get(con);
-          ListBase targets = {nullptr, nullptr};
-          if (cti && cti->get_constraint_targets) {

+          ListBase targets = {nullptr, nullptr};
+          if (BKE_constraint_targets_get(con, &targets)) {
            bConstraintTarget *ct;
            Object *obtar;

-            cti->get_constraint_targets(con, &targets);
-
            for (ct = (bConstraintTarget *)targets.first; ct; ct = ct->next) {
              obtar = ct->tar;
              std::string tar_id((obtar) ? id_name(obtar) : "");
              colladaNode.addExtraTechniqueChildParameter("blender", con_tag, "target_id", tar_id);
            }

-            if (cti->flush_constraint_targets) {
-              cti->flush_constraint_targets(con, &targets, true);
-            }
+            BKE_constraint_targets_flush(con, &targets, true);
          }

          con = con->next;
--- a/source/blender/makesdna/DNA_constraint_types.h
+++ b/source/blender/makesdna/DNA_constraint_types.h
@@ -61,12 +61,17 @@ typedef struct bConstraint {
  /** Space that target should be evaluated in (only used if 1 target). */
  char tarspace;

-  /** Constraint name, MAX_NAME. */
-  char name[64];
-
  /* An "expand" bit for each of the constraint's (sub)panels (uiPanelDataExpansion). */
  short ui_expand_flag;

+  /** Object to use as target for Custom Space of owner. */
+  struct Object *space_object;
+  /** Subtarget for Custom Space of owner - pchan or vgroup name, MAX_ID_NAME-2. */
+  char space_subtarget[64];
+
+  /** Constraint name, MAX_NAME. */
+  char name[64];
+
  /** Amount of influence exherted by constraint (0.0-1.0). */
  float enforce;
  /** Point along subtarget bone where the actual target is. 0=head (default for all), 1=tail. */
@@ -118,6 +123,8 @@ typedef struct bConstraintTarget {
 typedef enum eConstraintTargetFlag {
  /** temporary target-struct that needs to be freed after use */
  CONSTRAINT_TAR_TEMP = (1 << 0),
+  /** temporary target for the custom space reference */
+  CONSTRAINT_TAR_CUSTOM_SPACE = (1 << 1),
 } eConstraintTargetFlag;

 /* bConstraintTarget/bConstraintOb -> type */
@@ -722,6 +729,8 @@ typedef enum eBConstraint_Flags {
 typedef enum eBConstraint_SpaceTypes {
  /** Default for all - worldspace. */
  CONSTRAINT_SPACE_WORLD = 0,
+  /** For all - custom space. */
+  CONSTRAINT_SPACE_CUSTOM = 5,
  /**
   * For objects (relative to parent/without parent influence),
   * for bones (along normals of bone, without parent/rest-positions).
--- a/source/blender/makesrna/intern/rna_constraint.c
+++ b/source/blender/makesrna/intern/rna_constraint.c
@@ -200,6 +200,12 @@ static const EnumPropertyItem target_space_pchan_items[] = {
     "World Space",
     "The transformation of the target is evaluated relative to the world "
     "coordinate system"},
+    {CONSTRAINT_SPACE_CUSTOM,
+     "CUSTOM",
+     0,
+     "Custom Space",
+     "The transformation of the target is evaluated relative to a custom object/bone/vertex "
+     "group"},
    {CONSTRAINT_SPACE_POSE,
     "POSE",
     0,
@@ -227,6 +233,11 @@ static const EnumPropertyItem owner_space_pchan_items[] = {
     0,
     "World Space",
     "The constraint is applied relative to the world coordinate system"},
+    {CONSTRAINT_SPACE_CUSTOM,
+     "CUSTOM",
+     0,
+     "Custom Space",
+     "The constraint is applied in local space of a custom object/bone/vertex group"},
    {CONSTRAINT_SPACE_POSE,
     "POSE",
     0,
@@ -275,6 +286,12 @@ static const EnumPropertyItem space_object_items[] = {
     0,
     "World Space",
     "The transformation of the target is evaluated relative to the world coordinate system"},
+    {CONSTRAINT_SPACE_CUSTOM,
+     "CUSTOM",
+     0,
+     "Custom Space",
+     "The transformation of the target is evaluated relative to a custom object/bone/vertex "
+     "group"},
    {CONSTRAINT_SPACE_LOCAL,
     "LOCAL",
     0,
@@ -582,22 +599,17 @@ static const EnumPropertyItem *rna_Constraint_target_space_itemf(bContext *UNUSE
                                                                 bool *UNUSED(r_free))
 {
  bConstraint *con = (bConstraint *)ptr->data;
-  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 && ct->tar->type == OB_ARMATURE) {
+      if (ct->tar && ct->tar->type == OB_ARMATURE && !(ct->type & CONSTRAINT_TAR_CUSTOM_SPACE)) {
        break;
      }
    }

-    if (cti->flush_constraint_targets) {
-      cti->flush_constraint_targets(con, &targets, 1);
-    }
+    BKE_constraint_targets_flush(con, &targets, 1);

    if (ct) {
      return target_space_pchan_items;
@@ -3398,6 +3410,18 @@ void RNA_def_constraint(BlenderRNA *brna)
  RNA_def_property_ui_text(prop, "Target Space", "Space that target is evaluated in");
  RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");

+  prop = RNA_def_property(srna, "space_object", PROP_POINTER, PROP_NONE);
+  RNA_def_property_pointer_sdna(prop, NULL, "space_object");
+  RNA_def_property_ui_text(prop, "Object", "Object for Custom Space");
+  RNA_def_property_flag(prop, PROP_EDITABLE);
+  RNA_def_property_override_flag(prop, PROPOVERRIDE_OVERRIDABLE_LIBRARY);
+  RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_dependency_update");
+
+  prop = RNA_def_property(srna, "space_subtarget", PROP_STRING, PROP_NONE);
+  RNA_def_property_string_sdna(prop, NULL, "space_subtarget");
+  RNA_def_property_ui_text(prop, "Sub-Target", "Armature bone, mesh or lattice vertex group, ...");
+  RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_dependency_update");
+
  /* flags */
  prop = RNA_def_property(srna, "mute", PROP_BOOLEAN, PROP_NONE);
  RNA_def_property_boolean_sdna(prop, NULL, "flag", CONSTRAINT_OFF);
--- a/source/blender/makesrna/intern/rna_object_api.c
+++ b/source/blender/makesrna/intern/rna_object_api.c
@@ -324,8 +324,27 @@ static void rna_Object_mat_convert_space(Object *ob,
      return;
    }
  }
+  /* These checks are extra security, they should never occur. */
+  if (from == CONSTRAINT_SPACE_CUSTOM) {
+    const char *identifier = NULL;
+    RNA_enum_identifier(space_items, from, &identifier);
+    BKE_reportf(reports,
+                RPT_ERROR,
+                "'from_space' '%s' is invalid when no custom space is given!",
+                identifier);
+    return;
+  }
+  if (to == CONSTRAINT_SPACE_CUSTOM) {
+    const char *identifier = NULL;
+    RNA_enum_identifier(space_items, to, &identifier);
+    BKE_reportf(reports,
+                RPT_ERROR,
+                "'to_space' '%s' is invalid when no custom space is given!",
+                identifier);
+    return;
+  }

-  BKE_constraint_mat_convertspace(ob, pchan, (float(*)[4])mat_ret, from, to, false);
+  BKE_constraint_mat_convertspace(ob, pchan, NULL, (float(*)[4])mat_ret, from, to, false);
 }

 static void rna_Object_calc_matrix_camera(Object *ob,
--- a/tests/python/bl_constraints.py
+++ b/tests/python/bl_constraints.py
@@ -301,6 +301,80 @@ class ObjectSolverTest(AbstractConstraintTests):
        self.matrix_test('Object Solver.owner', initial_matrix)


+class CustomSpaceTest(AbstractConstraintTests):
+    layer_collection = 'Custom Space'
+
+    def test_loc_like_object(self):
+        """Custom Space: basic custom space evaluation for objects"""
+        loc_like_constraint = bpy.data.objects["Custom Space.object.owner"].constraints["Copy Location"]
+        loc_like_constraint.use_x = True
+        loc_like_constraint.use_y = True
+        loc_like_constraint.use_z = True
+        self.matrix_test('Custom Space.object.owner', Matrix((
+            (1.0, 0.0, -2.9802322387695312e-08, -0.01753106713294983),
+            (0.0, 1.0, 0.0, -0.08039519190788269),
+            (-2.9802322387695312e-08, 5.960464477539063e-08, 1.0, 0.1584688425064087),
+            (0.0, 0.0, 0.0, 1.0),
+        )))
+        loc_like_constraint.use_x = False
+        self.matrix_test('Custom Space.object.owner', Matrix((
+            (1.0, 0.0, -2.9802322387695312e-08, 0.18370598554611206),
+            (0.0, 1.0, 0.0, 0.47120195627212524),
+            (-2.9802322387695312e-08, 5.960464477539063e-08, 1.0, -0.16521614789962769),
+            (0.0, 0.0, 0.0, 1.0),
+        )))
+        loc_like_constraint.use_y = False
+        self.matrix_test('Custom Space.object.owner', Matrix((
+            (1.0, 0.0, -2.9802322387695312e-08, -0.46946945786476135),
+            (0.0, 1.0, 0.0, 0.423120379447937),
+            (-2.9802322387695312e-08, 5.960464477539063e-08, 1.0, -0.6532361507415771),
+            (0.0, 0.0, 0.0, 1.0),
+        )))
+        loc_like_constraint.use_z = False
+        loc_like_constraint.use_y = True
+        self.matrix_test('Custom Space.object.owner', Matrix((
+            (1.0, 0.0, -2.9802322387695312e-08, -0.346824586391449),
+            (0.0, 1.0, 0.0, 1.0480815172195435),
+            (-2.9802322387695312e-08, 5.960464477539063e-08, 1.0, 0.48802000284194946),
+            (0.0, 0.0, 0.0, 1.0),
+        )))
+
+    def test_loc_like_armature(self):
+        """Custom Space: basic custom space evaluation for bones"""
+        loc_like_constraint = bpy.data.objects["Custom Space.armature.owner"].pose.bones["Bone"].constraints["Copy Location"]
+        loc_like_constraint.use_x = True
+        loc_like_constraint.use_y = True
+        loc_like_constraint.use_z = True
+        self.bone_matrix_test('Custom Space.armature.owner', 'Bone', Matrix((
+            (0.4556015729904175, -0.03673229366540909, -0.8894257545471191, -0.01753103733062744),
+            (-0.45956411957740784, -0.8654094934463501, -0.19966775178909302, -0.08039522171020508),
+            (-0.762383222579956, 0.49971696734428406, -0.4111628830432892, 0.1584688425064087),
+            (0.0, 0.0, 0.0, 1.0),
+        )))
+        loc_like_constraint.use_x = False
+        self.bone_matrix_test('Custom Space.armature.owner', 'Bone', Matrix((
+            (0.4556015729904175, -0.03673229366540909, -0.8894257545471191, -0.310153603553772),
+            (-0.45956411957740784, -0.8654094934463501, -0.19966775178909302, -0.8824828863143921),
+            (-0.762383222579956, 0.49971696734428406, -0.4111628830432892, 0.629145085811615),
+            (0.0, 0.0, 0.0, 1.0),
+        )))
+        loc_like_constraint.use_y = False
+        self.bone_matrix_test('Custom Space.armature.owner', 'Bone', Matrix((
+            (0.4556015729904175, -0.03673229366540909, -0.8894257545471191, -1.0574829578399658),
+            (-0.45956411957740784, -0.8654094934463501, -0.19966775178909302, -0.937495231628418),
+            (-0.762383222579956, 0.49971696734428406, -0.4111628830432892, 0.07077804207801819),
+            (0.0, 0.0, 0.0, 1.0),
+        )))
+        loc_like_constraint.use_z = False
+        loc_like_constraint.use_y = True
+        self.bone_matrix_test('Custom Space.armature.owner', 'Bone', Matrix((
+            (0.4556015729904175, -0.03673229366540909, -0.8894257545471191, -0.25267064571380615),
+            (-0.45956411957740784, -0.8654094934463501, -0.19966775178909302, -0.9449876546859741),
+            (-0.762383222579956, 0.49971696734428406, -0.4111628830432892, 0.5583670735359192),
+            (0.0, 0.0, 0.0, 1.0),
+        )))
+
+
 def main():
    global args
    import argparse