Context: implement an active_action property that returns a single action.

Although e.g. in the dopesheet there is no specific concept of
active action, displaying panels requires singling out one action
reference. It is more efficient and clearer to implement this
natively in the context rather than using selected_visible_actions[0].

- In the Action Editor the action is taken from the header.
- In the Dope Sheet the first selected action is chosen, because
  there is no concept of an active channel or keyframe.
- In the Graph Editor the action associated with the active curve
  is used, which should also be associated with the active vertex.
  This case may be different from selected_visible_actions[0].

Differential Revision: https://developer.blender.org/D15412

2 files changed, 40 insertions, 18 deletions

diff --git a/release/scripts/startup/bl_ui/space_dopesheet.py b/release/scripts/startup/bl_ui/space_dopesheet.py
index a1c086db745..4d1514c2777 100644
--- a/release/scripts/startup/bl_ui/space_dopesheet.py
+++ b/release/scripts/startup/bl_ui/space_dopesheet.py
@@ -567,10 +567,10 @@ class DOPESHEET_PT_action(DopesheetActionPanelBase, Panel):
 
     @classmethod
     def poll(cls, context):
-        return bool(context.selected_visible_actions)
+        return bool(context.active_action)
 
     def draw(self, context):
-        action = context.selected_visible_actions[0]
+        action = context.active_action
         self.draw_generic_panel(context, self.layout, action)
 
 
diff --git a/source/blender/editors/screen/screen_context.c b/source/blender/editors/screen/screen_context.c
index 239113c28a4..0d6b6ee1d78 100644
--- a/source/blender/editors/screen/screen_context.c
+++ b/source/blender/editors/screen/screen_context.c
@@ -100,6 +100,7 @@ const char *screen_context_dir[] = {
     "active_gpencil_frame",
     "active_annotation_layer",
     "active_operator",
+    "active_action",
     "selected_visible_actions",
     "selected_editable_actions",
     "visible_fcurves",
@@ -969,6 +970,7 @@ static eContextResult screen_ctx_active_operator(const bContext *C, bContextData
 }
 static eContextResult screen_ctx_sel_actions_impl(const bContext *C,
                                                   bContextDataResult *result,
+                                                  bool active_only,
                                                   bool editable)
 {
   bAnimContext ac;
@@ -978,11 +980,17 @@ static eContextResult screen_ctx_sel_actions_impl(const bContext *C,
       SpaceAction *saction = (SpaceAction *)ac.sl;
 
       if (ELEM(saction->mode, SACTCONT_ACTION, SACTCONT_SHAPEKEY)) {
-        if (saction->action && !(editable && ID_IS_LINKED(saction->action))) {
-          CTX_data_id_list_add(result, &saction->action->id);
+        if (active_only) {
+          CTX_data_id_pointer_set(result, (ID *)saction->action);
+        }
+        else {
+          if (saction->action && !(editable && ID_IS_LINKED(saction->action))) {
+            CTX_data_id_list_add(result, &saction->action->id);
+          }
+
+          CTX_data_type_set(result, CTX_DATA_TYPE_COLLECTION);
         }
 
-        CTX_data_type_set(result, CTX_DATA_TYPE_COLLECTION);
         return CTX_RESULT_OK;
       }
     }
@@ -995,7 +1003,8 @@ static eContextResult screen_ctx_sel_actions_impl(const bContext *C,
 
     switch (ac.spacetype) {
       case SPACE_GRAPH:
-        filter |= ANIMFILTER_FCURVESONLY | ANIMFILTER_CURVE_VISIBLE | ANIMFILTER_SEL;
+        filter |= ANIMFILTER_FCURVESONLY | ANIMFILTER_CURVE_VISIBLE |
+                  (active_only ? ANIMFILTER_ACTIVE : ANIMFILTER_SEL);
         break;
 
       case SPACE_ACTION:
@@ -1006,7 +1015,7 @@ static eContextResult screen_ctx_sel_actions_impl(const bContext *C,
 
     ANIM_animdata_filter(&ac, &anim_data, filter, ac.data, ac.datatype);
 
-    GSet *seen_set = BLI_gset_ptr_new("seen actions");
+    GSet *seen_set = active_only ? NULL : BLI_gset_ptr_new("seen actions");
 
     LISTBASE_FOREACH (bAnimListElem *, ale, &anim_data) {
       /* In dopesheet check selection status of individual items, skipping
@@ -1019,36 +1028,48 @@ static eContextResult screen_ctx_sel_actions_impl(const bContext *C,
       bAction *action = ANIM_channel_action_get(ale);
 
       if (action) {
-        if (editable && ID_IS_LINKED(action)) {
-          continue;
+        if (active_only) {
+          CTX_data_id_pointer_set(result, (ID *)action);
+          break;
         }
+        else {
+          if (editable && ID_IS_LINKED(action)) {
+            continue;
+          }
 
-        /* Add the action to the output list if not already added. */
-        if (BLI_gset_add(seen_set, action)) {
-          CTX_data_id_list_add(result, &action->id);
+          /* Add the action to the output list if not already added. */
+          if (BLI_gset_add(seen_set, action)) {
+            CTX_data_id_list_add(result, &action->id);
+          }
         }
       }
     }
 
-    BLI_gset_free(seen_set, NULL);
-
     ANIM_animdata_freelist(&anim_data);
 
-    CTX_data_type_set(result, CTX_DATA_TYPE_COLLECTION);
+    if (!active_only) {
+      BLI_gset_free(seen_set, NULL);
+
+      CTX_data_type_set(result, CTX_DATA_TYPE_COLLECTION);
+    }
+
     return CTX_RESULT_OK;
   }
   return CTX_RESULT_NO_DATA;
 }
-
+static eContextResult screen_ctx_active_action(const bContext *C, bContextDataResult *result)
+{
+  return screen_ctx_sel_actions_impl(C, result, true, false);
+}
 static eContextResult screen_ctx_selected_visible_actions(const bContext *C,
                                                           bContextDataResult *result)
 {
-  return screen_ctx_sel_actions_impl(C, result, false);
+  return screen_ctx_sel_actions_impl(C, result, false, false);
 }
 static eContextResult screen_ctx_selected_editable_actions(const bContext *C,
                                                            bContextDataResult *result)
 {
-  return screen_ctx_sel_actions_impl(C, result, true);
+  return screen_ctx_sel_actions_impl(C, result, false, true);
 }
 static eContextResult screen_ctx_sel_edit_fcurves_(const bContext *C,
                                                    bContextDataResult *result,
@@ -1262,6 +1283,7 @@ static void ensure_ed_screen_context_functions(void)
   register_context_function("editable_gpencil_layers", screen_ctx_editable_gpencil_layers);
   register_context_function("editable_gpencil_strokes", screen_ctx_editable_gpencil_strokes);
   register_context_function("active_operator", screen_ctx_active_operator);
+  register_context_function("active_action", screen_ctx_active_action);
   register_context_function("selected_visible_actions", screen_ctx_selected_visible_actions);
   register_context_function("selected_editable_actions", screen_ctx_selected_editable_actions);
   register_context_function("editable_fcurves", screen_ctx_editable_fcurves);