Anim: UI template for Action selectors

This PR is just taken over from @dr.sybren with
minor comments addressed.

Original PR: #125493

Co-authored-by: Sybren A. Stüvel <sybren@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/126561

scripts/startup/bl_ui/space_dopesheet.py

@@ -243,7 +243,7 @@ class DOPESHEET_HT_editor_buttons:
 
             layout.separator_spacer()
 
-            layout.template_ID(st, "action", new="action.new", unlink="action.unlink")
+            layout.template_action(context.object, new="action.new", unlink="action.unlink")
 
             # Show slot selector.
             if context.preferences.experimental.use_animation_baklava:

source/blender/editors/include/UI_interface_c.hh

@@ -2495,6 +2495,23 @@ void uiTemplateAnyID(uiLayout *layout,
                      const char *propname,
                      const char *proptypename,
                      const char *text);
+
+/**
+ * Action selector.
+ *
+ * This is a specialisation of #uiTemplateID, hard-coded to assign Actions to the given ID.
+ * Such a specialisation is necessary, as the RNA property (`id.animation_data.action`) does not
+ * exist when the ID's `adt` pointer is `nullptr`. In that case uiTemplateID will not be able
+ * to find the RNA type of that property, which in turn it needs to determine the type of IDs to
+ * show.
+ */
+void uiTemplateAction(uiLayout *layout,
+                      const bContext *C,
+                      ID *id,
+                      const char *newop,
+                      const char *unlinkop,
+                      const char *text);
+
 /**
  * Search menu to pick an item from a collection.
  * A version of uiTemplateID that works for non-ID types.
@@ -3236,7 +3253,7 @@ void UI_context_active_but_prop_get_filebrowser(const bContext *C,
  *
  * This is for browsing and editing the ID-blocks used.
  */
-void UI_context_active_but_prop_get_templateID(bContext *C,
+void UI_context_active_but_prop_get_templateID(const bContext *C,
                                                PointerRNA *r_ptr,
                                                PropertyRNA **r_prop);
 ID *UI_context_active_but_get_tab_ID(bContext *C);

source/blender/editors/interface/templates/interface_templates.cc

@@ -16,6 +16,7 @@
 
 #include "MEM_guardedalloc.h"
 
+#include "DNA_anim_types.h"
 #include "DNA_brush_types.h"
 #include "DNA_cachefile_types.h"
 #include "DNA_collection_types.h"
@@ -44,6 +45,7 @@
 #include "BLF_api.hh"
 #include "BLT_translation.hh"
 
+#include "BKE_anim_data.hh"
 #include "BKE_blender_version.h"
 #include "BKE_blendfile.hh"
 #include "BKE_colorband.hh"
@@ -545,7 +547,7 @@ static uiBlock *id_search_menu(bContext *C, ARegion *region, void *arg_litem)
 
 static void template_id_cb(bContext *C, void *arg_litem, void *arg_event);
 
-void UI_context_active_but_prop_get_templateID(bContext *C,
+void UI_context_active_but_prop_get_templateID(const bContext *C,
                                                PointerRNA *r_ptr,
                                                PropertyRNA **r_prop)
 {
@@ -1818,6 +1820,54 @@ void uiTemplateID(uiLayout *layout,
                  false);
 }
 
+void uiTemplateAction(uiLayout *layout,
+                      const bContext *C,
+                      ID *id,
+                      const char *newop,
+                      const char *unlinkop,
+                      const char *text)
+{
+  if (!id_can_have_animdata(id)) {
+    RNA_warning("Cannot show Action selector for non-animatable ID: %s", id->name + 2);
+    return;
+  }
+
+  PropertyRNA *adt_action_prop = RNA_struct_type_find_property(&RNA_AnimData, "action");
+  BLI_assert(adt_action_prop);
+  BLI_assert(RNA_property_type(adt_action_prop) == PROP_POINTER);
+
+  /* Construct a pointer with the animated ID as owner, even when `adt` may be `nullptr`.
+   * This way it is possible to use this RNA pointer to get/set `adt->action`, as that RNA property
+   * has a getter and setter that only need the owner ID and are null-safe regarding the `adt`
+   * itself. */
+  AnimData *adt = BKE_animdata_from_id(id);
+  PointerRNA adt_ptr = RNA_pointer_create(id, &RNA_AnimData, adt);
+
+  /* This must be heap-allocated because template_ID() will call MEM_dupallocN()
+   * on the pointer we pass, and that doesn't like stack-allocated stuff. */
+  TemplateID *template_ui = MEM_cnew<TemplateID>(__func__);
+  BLI_SCOPED_DEFER([&]() { MEM_freeN(template_ui); });
+  template_ui->ptr = adt_ptr;
+  template_ui->prop = adt_action_prop;
+  template_ui->prv_rows = 0;
+  template_ui->prv_cols = 0;
+  template_ui->scale = 1.0f;
+  template_ui->filter = UI_TEMPLATE_ID_FILTER_ALL;
+
+  int flag = UI_ID_BROWSE | UI_ID_RENAME | UI_ID_DELETE;
+  if (newop) {
+    flag |= UI_ID_ADD_NEW;
+  }
+
+  template_ui->idcode = ID_AC;
+  template_ui->idlb = which_libbase(CTX_data_main(C), ID_AC);
+  BLI_assert(template_ui->idlb);
+
+  uiLayout *row = uiLayoutRow(layout, true);
+  template_ID(
+      C, row, template_ui, &RNA_Action, flag, newop, nullptr, unlinkop, text, false, false);
+}
+
 void uiTemplateIDBrowse(uiLayout *layout,
                         bContext *C,
                         PointerRNA *ptr,

source/blender/editors/space_action/action_data.cc

@@ -43,6 +43,7 @@
 #include "WM_types.hh"
 
 #include "UI_interface.hh"
+#include "UI_interface_c.hh"
 
 #include "action_intern.hh"
 
@@ -52,7 +53,29 @@
 
 AnimData *ED_actedit_animdata_from_context(const bContext *C, ID **r_adt_id_owner)
 {
+  { /* Support use from the layout.template_action() UI template. */
+    PointerRNA ptr = {nullptr};
+    PropertyRNA *prop = nullptr;
+    UI_context_active_but_prop_get_templateID(C, &ptr, &prop);
+    /* template_action() sets a RNA_AnimData pointer, whereas other code may set
+     * other pointer types. This code here only deals with the former. */
+    if (prop && ptr.type == &RNA_AnimData) {
+      if (!RNA_property_editable(&ptr, prop)) {
+        return nullptr;
+      }
+      if (r_adt_id_owner) {
+        *r_adt_id_owner = ptr.owner_id;
+      }
+      AnimData *adt = static_cast<AnimData *>(ptr.data);
+      return adt;
+    }
+  }
+
   SpaceAction *saction = (SpaceAction *)CTX_wm_space_data(C);
+  if (!saction) {
+    return nullptr;
+  }
+
   Object *ob = CTX_data_active_object(C);
   AnimData *adt = nullptr;
 
@@ -159,6 +182,15 @@ static void actedit_change_action(bContext *C, bAction *act)
 
 static bool action_new_poll(bContext *C)
 {
+  { /* Support use from the layout.template_action() UI template. */
+    PointerRNA ptr = {nullptr};
+    PropertyRNA *prop = nullptr;
+    UI_context_active_but_prop_get_templateID(C, &ptr, &prop);
+    if (prop) {
+      return RNA_property_editable(&ptr, prop);
+    }
+  }
+
   Scene *scene = CTX_data_scene(C);
 
   /* Check tweak-mode is off (as you don't want to be tampering with the action in that case) */
@@ -569,6 +601,7 @@ void ACTION_OT_stash_and_create(wmOperatorType *ot)
 void ED_animedit_unlink_action(
     bContext *C, ID *id, AnimData *adt, bAction *act, ReportList *reports, bool force_delete)
 {
+  BLI_assert(id);
   ScrArea *area = CTX_wm_area(C);
 
   /* If the old action only has a single user (that it's about to lose),
@@ -654,6 +687,20 @@ void ED_animedit_unlink_action(
 
 static bool action_unlink_poll(bContext *C)
 {
+  {
+    ID *animated_id = nullptr;
+    AnimData *adt = ED_actedit_animdata_from_context(C, &animated_id);
+    if (animated_id) {
+      if (!BKE_id_is_editable(CTX_data_main(C), animated_id)) {
+        return false;
+      }
+      if (!adt) {
+        return false;
+      }
+      return adt->action != nullptr;
+    }
+  }
+
   if (ED_operator_action_active(C)) {
     SpaceAction *saction = (SpaceAction *)CTX_wm_space_data(C);
     AnimData *adt = ED_actedit_animdata_from_context(C, nullptr);
@@ -670,11 +717,12 @@ static bool action_unlink_poll(bContext *C)
 
 static int action_unlink_exec(bContext *C, wmOperator *op)
 {
-  AnimData *adt = ED_actedit_animdata_from_context(C, nullptr);
+  ID *animated_id = nullptr;
+  AnimData *adt = ED_actedit_animdata_from_context(C, &animated_id);
   bool force_delete = RNA_boolean_get(op->ptr, "force_delete");
 
   if (adt && adt->action) {
-    ED_animedit_unlink_action(C, nullptr, adt, adt->action, op->reports, force_delete);
+    ED_animedit_unlink_action(C, animated_id, adt, adt->action, op->reports, force_delete);
   }
 
   /* Unlink is also abused to exit NLA tweak mode. */

source/blender/makesrna/intern/rna_animation.cc

@@ -143,10 +143,24 @@ static void rna_AnimData_dependency_update(Main *bmain, Scene *scene, PointerRNA
 
 static int rna_AnimData_action_editable(const PointerRNA *ptr, const char ** /*r_info*/)
 {
-  AnimData *adt = (AnimData *)ptr->data;
+  BLI_assert(ptr->type == &RNA_AnimData);
+  AnimData *adt = static_cast<AnimData *>(ptr->data);
+  if (!adt) {
+    return PROP_EDITABLE;
+  }
   return BKE_animdata_action_editable(adt) ? PROP_EDITABLE : PropertyFlag(0);
 }
 
+static PointerRNA rna_AnimData_action_get(PointerRNA *ptr)
+{
+  ID &animated_id = *ptr->owner_id;
+  animrig::Action *action = animrig::get_action(animated_id);
+  if (!action) {
+    return PointerRNA_NULL;
+  };
+  return RNA_id_pointer_create(&action->id);
+}
+
 static void rna_AnimData_action_set(PointerRNA *ptr, PointerRNA value, ReportList * /*reports*/)
 {
 #  ifdef WITH_ANIM_BAKLAVA
@@ -1563,10 +1577,21 @@ static void rna_def_animdata(BlenderRNA *brna)
 
   /* Active Action */
   prop = RNA_def_property(srna, "action", PROP_POINTER, PROP_NONE);
+  RNA_def_property_struct_type(prop, "Action");
   /* this flag as well as the dynamic test must be defined for this to be editable... */
   RNA_def_property_flag(prop, PROP_EDITABLE | PROP_ID_REFCOUNT);
   RNA_def_property_pointer_funcs(
-      prop, nullptr, "rna_AnimData_action_set", nullptr, "rna_Action_id_poll");
+      prop,
+      /* Define a getter that is NULL-safe, so that an RNA_AnimData prop with `ptr->data = nullptr`
+       * can still be used to get the property. In that case it will always return nullptr, of
+       * course, but it won't crash Blender. */
+      "rna_AnimData_action_get",
+      /* Similarly, for the setter, the NULL-safety allows constructing the AnimData struct on
+       * assignment of this "action" property. This is possible because RNA has typed NULL
+       * pointers, and thus it knows which setter to call even when `ptr->data` is NULL. */
+      "rna_AnimData_action_set",
+      nullptr,
+      "rna_Action_id_poll");
   RNA_def_property_editable_func(prop, "rna_AnimData_action_editable");
   RNA_def_property_ui_text(prop, "Action", "Active Action for this data-block");
   RNA_def_property_update(prop, NC_ANIMATION | ND_NLA_ACTCHANGE, "rna_AnimData_dependency_update");

source/blender/makesrna/intern/rna_ui_api.cc

@@ -576,6 +576,19 @@ static void rna_uiTemplateAnyID(uiLayout *layout,
   uiTemplateAnyID(layout, ptr, propname, proptypename, name);
 }
 
+static void rna_uiTemplateAction(uiLayout *layout,
+                                 bContext *C,
+                                 ID *id,
+                                 const char *newop,
+                                 const char *unlinkop,
+                                 const char *name,
+                                 const char *text_ctxt,
+                                 const bool translate)
+{
+  name = rna_translate_ui_text(name, text_ctxt, nullptr, nullptr, translate);
+  uiTemplateAction(layout, C, id, newop, unlinkop, name);
+}
+
 void rna_uiTemplateList(uiLayout *layout,
                         bContext *C,
                         const char *listtype_name,
@@ -1716,6 +1729,14 @@ void RNA_api_ui_layout(StructRNA *srna)
                "",
                "Optionally limit the items which can be selected");
 
+  func = RNA_def_function(srna, "template_action", "rna_uiTemplateAction");
+  RNA_def_function_flag(func, FUNC_USE_CONTEXT);
+  parm = RNA_def_pointer(func, "id", "ID", "", "The data-block for which to select an Action");
+  RNA_def_parameter_flags(parm, PROP_NEVER_NULL, PARM_REQUIRED);
+  RNA_def_string(func, "new", nullptr, 0, "", "Operator identifier to create a new ID block");
+  RNA_def_string(func, "unlink", nullptr, 0, "", "Operator identifier to unlink the ID block");
+  api_ui_item_common_text(func);
+
   func = RNA_def_function(srna, "template_search", "uiTemplateSearch");
   RNA_def_function_flag(func, FUNC_USE_CONTEXT);
   api_ui_item_rna_common(func);