Fix T69573: Driver Value does not slide along the actual value in the Driver Editor

This change is two-fold:

- Ensure the result of the F-Curve evaluation is stored on the FCurve
  object. This was done in 2.79 but lost when we moved to more granular
  per-curve evaluation from the depsgraph.
- Flush this result from the CoW copy back to the original.

Reviewed by: sergey

Differential Revision: https://developer.blender.org/D5888

source/blender/blenkernel/BKE_animsys.h

@@ -289,7 +289,7 @@ void BKE_animsys_eval_animdata(struct Depsgraph *depsgraph, struct ID *id);
 void BKE_animsys_eval_driver(struct Depsgraph *depsgraph,
                              struct ID *id,
                              int driver_index,
-                             struct ChannelDriver *driver_orig);
+                             struct FCurve *fcu_orig);
 
 void BKE_animsys_update_driver_array(struct ID *id);
 

source/blender/blenkernel/intern/anim_sys.c

@@ -4082,11 +4082,10 @@ void BKE_animsys_update_driver_array(ID *id)
   }
 }
 
-void BKE_animsys_eval_driver(Depsgraph *depsgraph,
-                             ID *id,
-                             int driver_index,
-                             ChannelDriver *driver_orig)
+void BKE_animsys_eval_driver(Depsgraph *depsgraph, ID *id, int driver_index, FCurve *fcu_orig)
 {
+  BLI_assert(fcu_orig != NULL);
+
   /* TODO(sergey): De-duplicate with BKE animsys. */
   PointerRNA id_ptr;
   bool ok = false;
@@ -4111,6 +4110,7 @@ void BKE_animsys_eval_driver(Depsgraph *depsgraph,
   if ((fcu->flag & (FCURVE_MUTED | FCURVE_DISABLED)) == 0) {
     /* check if driver itself is tagged for recalculation */
     /* XXX driver recalc flag is not set yet by depsgraph! */
+    ChannelDriver *driver_orig = fcu_orig->driver;
     if ((driver_orig) && !(driver_orig->flag & DRIVER_FLAG_INVALID)) {
       /* evaluate this using values set already in other places
        * NOTE: for 'layering' option later on, we should check if we should remove old value before
@@ -4121,7 +4121,7 @@ void BKE_animsys_eval_driver(Depsgraph *depsgraph,
       if (animsys_store_rna_setting(&id_ptr, fcu->rna_path, fcu->array_index, &anim_rna)) {
         /* Evaluate driver, and write results to COW-domain destination */
         const float ctime = DEG_get_ctime(depsgraph);
-        const float curval = evaluate_fcurve_driver(&anim_rna, fcu, driver_orig, ctime);
+        const float curval = calculate_fcurve(&anim_rna, fcu, ctime);
         ok = animsys_write_rna_setting(&anim_rna, curval);
 
         /* Flush results & status codes to original data for UI (T59984) */
@@ -4129,6 +4129,7 @@ void BKE_animsys_eval_driver(Depsgraph *depsgraph,
           animsys_write_orig_anim_rna(&id_ptr, fcu->rna_path, fcu->array_index, curval);
 
           /* curval is displayed in the UI, and flag contains error-status codes */
+          fcu_orig->curval = fcu->curval;
           driver_orig->curval = fcu->driver->curval;
           driver_orig->flag = fcu->driver->flag;
 

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

@@ -900,19 +900,17 @@ void DepsgraphNodeBuilder::build_driver(ID *id, FCurve *fcurve, int driver_index
 {
   /* Create data node for this driver */
   ID *id_cow = get_cow_id(id);
-  ChannelDriver *driver_orig = fcurve->driver;
 
   /* TODO(sergey): ideally we could pass the COW of fcu, but since it
    * has not yet been allocated at this point we can't. As a workaround
    * the animation systems allocates an array so we can do a fast lookup
    * with the driver index. */
-  ensure_operation_node(
-      id,
-      NodeType::PARAMETERS,
-      OperationCode::DRIVER,
-      function_bind(BKE_animsys_eval_driver, _1, id_cow, driver_index, driver_orig),
-      fcurve->rna_path ? fcurve->rna_path : "",
-      fcurve->array_index);
+  ensure_operation_node(id,
+                        NodeType::PARAMETERS,
+                        OperationCode::DRIVER,
+                        function_bind(BKE_animsys_eval_driver, _1, id_cow, driver_index, fcurve),
+                        fcurve->rna_path ? fcurve->rna_path : "",
+                        fcurve->array_index);
   build_driver_variables(id, fcurve);
 }