diff options
| -rw-r--r-- | source/blender/depsgraph/intern/builder/deg_builder_relations.cc | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/source/blender/depsgraph/intern/builder/deg_builder_relations.cc b/source/blender/depsgraph/intern/builder/deg_builder_relations.cc index c16325b7299..c13c6d2f870 100644 --- a/source/blender/depsgraph/intern/builder/deg_builder_relations.cc +++ b/source/blender/depsgraph/intern/builder/deg_builder_relations.cc @@ -1711,6 +1711,37 @@ void DepsgraphRelationBuilder::build_driver_variables(ID *id, FCurve *fcu) } add_relation(variable_exit_key, driver_key, "RNA Target -> Driver"); + /* It is possible that RNA path points to a property of a different ID than the target_id: + * for example, paths like "data" on Object, "camera" on Scene. + * + * For the demonstration purposes lets consider a driver variable uses Scene ID as target + * and "camera.location.x" as its RNA path. If the scene has 2 different cameras at + * 2 different locations changing the active scene camera is expected to immediately be + * reflected in the variable value. In order to achieve this behavior we create a relation + * from the target ID to the driver so that if the ID property of the target ID changes the + * driver is re-evaluated. + * + * The most straightforward (at the moment of writing this comment) way of figuring out + * such relation is to use copy-on-write operation of the target ID. There are two down + * sides of this approach which are considered a design limitation as there is a belief + * that they are not common in practice or are not reliable due to other issues: + * + * - IDs which are not covered with the copy-on-write mechanism. + * + * Such IDs are either do not have ID properties, or are not part of the dependency + * graph. + * + * - Modifications of evaluated IDs from a Python handler. + * Such modifications are not fully integrated in the dependency graph evaluation as it + * has issues with copy-on-write tagging and the fact that relations are defined by the + * original main database status. */ + if (target_id != variable_exit_key.ptr.owner_id) { + if (deg_copy_on_write_is_needed(GS(target_id->name))) { + ComponentKey target_id_key(target_id, NodeType::COPY_ON_WRITE); + add_relation(target_id_key, driver_key, "Target ID -> Driver"); + } + } + /* The RNA getter for `object.data` can write to the mesh datablock due * to the call to `BKE_mesh_wrapper_ensure_subdivision()`. This relation * ensures it is safe to call when the driver is evaluated. |