Anim: add Action+Slot selector for Masks

This adds an Animation panel to the Mask tab of the n-panel of the
Movie Clip and Image editors. Masks can be animated (for example, the
opacity of a Mask Layer), but there was no way to manage the Action
and Slot that held those F-Curves.

To keep things DRY, this PR also moves the code for drawing Action+Slot
selectors from the `PropertiesAnimationMixin` class to a utility
function, which is now called from both that class and the Mask UI code.

Pull Request: https://projects.blender.org/blender/blender/pulls/133153

scripts/startup/bl_ui/anim.py

@@ -5,6 +5,33 @@
 from bpy.types import Menu
 
 
+def draw_action_and_slot_selector_for_id(layout, animated_id):
+    """
+    Draw the action and slot selector for an ID, using the given layout.
+
+    The ID must be an animatable ID.
+
+    Note that the slot selector is only drawn when the ID has an assigned
+    Action.
+    """
+
+    layout.template_action(animated_id, new="action.new", unlink="action.unlink")
+
+    adt = animated_id.animation_data
+    if not adt or not adt.action:
+        return
+
+    # Only show the slot selector when a layered Action is assigned.
+    if adt.action.is_action_layered:
+        layout.context_pointer_set("animated_id", animated_id)
+        layout.template_search(
+            adt, "action_slot",
+            adt, "action_suitable_slots",
+            new="anim.slot_new_for_id",
+            unlink="anim.slot_unassign_from_id",
+        )
+
+
 class ANIM_MT_keyframe_insert_pie(Menu):
     bl_label = "Keyframe Insert Pie"
 

scripts/startup/bl_ui/properties_mask_common.py

@@ -7,6 +7,7 @@
 
 from bpy.types import Menu, UIList
 from bpy.app.translations import contexts as i18n_contexts
+from . import anim
 
 
 # Use by both image & clip context menus.
@@ -222,6 +223,31 @@ class MASK_PT_point:
                 )
 
 
+class MASK_PT_animation:
+    # subclasses must define...
+    # ~ bl_space_type = 'CLIP_EDITOR'
+    # ~ bl_region_type = 'UI'
+    bl_label = "Animation"
+    bl_options = {'DEFAULT_CLOSED'}
+
+    @classmethod
+    def poll(cls, context):
+        space_data = context.space_data
+        return space_data.mask and space_data.mode == 'MASK'
+
+    def draw(self, context):
+        layout = self.layout
+        layout.use_property_split = True
+        layout.use_property_decorate = False
+
+        # poll() ensures this is not None.
+        sc = context.space_data
+        mask = sc.mask
+
+        col = layout.column(align=True)
+        anim.draw_action_and_slot_selector_for_id(col, mask)
+
+
 class MASK_PT_display:
     # subclasses must define...
     # ~ bl_space_type = 'CLIP_EDITOR'

scripts/startup/bl_ui/space_clip.py

@@ -1191,6 +1191,7 @@ from bl_ui.properties_mask_common import (
     MASK_PT_layers,
     MASK_PT_spline,
     MASK_PT_point,
+    MASK_PT_animation,
     MASK_PT_display,
     MASK_PT_transforms,
     MASK_PT_tools,
@@ -1215,6 +1216,12 @@ class CLIP_PT_active_mask_point(MASK_PT_point, Panel):
     bl_category = "Mask"
 
 
+class CLIP_PT_mask_animation(MASK_PT_animation, Panel):
+    bl_space_type = 'CLIP_EDITOR'
+    bl_region_type = 'UI'
+    bl_category = "Mask"
+
+
 class CLIP_PT_mask(MASK_PT_mask, Panel):
     bl_space_type = 'CLIP_EDITOR'
     bl_region_type = 'UI'
@@ -1996,6 +2003,7 @@ classes = (
     CLIP_PT_mask_display,
     CLIP_PT_active_mask_spline,
     CLIP_PT_active_mask_point,
+    CLIP_PT_mask_animation,
     CLIP_PT_tools_mask_transforms,
     CLIP_PT_tools_mask_tools,
     CLIP_PT_tools_scenesetup,

scripts/startup/bl_ui/space_image.py

@@ -987,6 +987,7 @@ from bl_ui.properties_mask_common import (
     MASK_PT_layers,
     MASK_PT_spline,
     MASK_PT_point,
+    MASK_PT_animation,
     MASK_PT_display,
 )
 
@@ -1015,6 +1016,12 @@ class IMAGE_PT_active_mask_point(MASK_PT_point, Panel):
     bl_category = "Mask"
 
 
+class IMAGE_PT_mask_animation(MASK_PT_animation, Panel):
+    bl_space_type = 'IMAGE_EDITOR'
+    bl_region_type = 'UI'
+    bl_category = "Mask"
+
+
 class IMAGE_PT_mask_display(MASK_PT_display, Panel):
     bl_space_type = 'IMAGE_EDITOR'
     bl_region_type = 'HEADER'
@@ -1771,6 +1778,7 @@ classes = (
     IMAGE_PT_mask_display,
     IMAGE_PT_active_mask_spline,
     IMAGE_PT_active_mask_point,
+    IMAGE_PT_mask_animation,
     IMAGE_PT_snapping,
     IMAGE_PT_proportional_edit,
     IMAGE_PT_image_properties,

scripts/startup/bl_ui/space_properties.py

@@ -4,6 +4,7 @@
 
 from bpy.types import Header, Panel
 from rna_prop_ui import PropertyPanel
+from . import anim
 
 
 class PROPERTIES_HT_header(Header):
@@ -122,21 +123,7 @@ class PropertiesAnimationMixin:
             layout.label(text="No animatable data-block, please report as bug", icon='ERROR')
             return
 
-        layout.template_action(animated_id, new="action.new", unlink="action.unlink")
+        anim.draw_action_and_slot_selector_for_id(layout, animated_id)
-
-        adt = animated_id.animation_data
-        if not adt or not adt.action:
-            return
-
-        # Only show the slot selector when a layered Action is assigned.
-        if adt.action.is_action_layered:
-            layout.context_pointer_set("animated_id", animated_id)
-            layout.template_search(
-                adt, "action_slot",
-                adt, "action_suitable_slots",
-                new="anim.slot_new_for_id",
-                unlink="anim.slot_unassign_from_id",
-            )
 
 
 classes = (