Fix #110879: Multires relative subdivide navigation subdivides mesh

Prior to this commit, the `object.subdivision_set` would prevent
actually applying a subdivision to a multires modifier when the relative
option was set. This is commonly accessed via Alt-1 / Alt-2 or D / Shift
D in Sculpt mode.

However, when the multires modifier did not already exist, pressing
these keybinds would still create the modifier and further subdivide the
mesh.

To fix this, this commit adds a hidden property to the operator:
`ensure_modifier` to indicate if the keybind should create the modifier
or not.

Pull Request: https://projects.blender.org/blender/blender/pulls/130254

scripts/presets/keyconfig/keymap_data/blender_default.py

@@ -5112,9 +5112,9 @@ def km_sculpt(params):
         # Subdivision levels
         *_template_items_object_subdivision_set(),
         ("object.subdivision_set", {"type": 'ONE', "value": 'PRESS', "alt": True, "repeat": True},
-         {"properties": [("level", -1), ("relative", True)]}),
+         {"properties": [("level", -1), ("relative", True), ("ensure_modifier", False)]}),
         ("object.subdivision_set", {"type": 'TWO', "value": 'PRESS', "alt": True, "repeat": True},
-         {"properties": [("level", 1), ("relative", True)]}),
+         {"properties": [("level", 1), ("relative", True), ("ensure_modifier", False)]}),
         # Mask
         ("paint.mask_flood_fill", {"type": 'M', "value": 'PRESS', "alt": True},
          {"properties": [("mode", 'VALUE'), ("value", 0.0)]}),

scripts/presets/keyconfig/keymap_data/industry_compatible_data.py

@@ -2947,9 +2947,9 @@ def km_sculpt(params):
         # Subdivision levels
         *_template_items_object_subdivision_set(),
         ("object.subdivision_set", {"type": 'D', "value": 'PRESS', "repeat": True},
-         {"properties": [("level", 1), ("relative", True)]}),
+         {"properties": [("level", 1), ("relative", True), ("ensure_modifier", False)]}),
         ("object.subdivision_set", {"type": 'D', "value": 'PRESS', "shift": True, "repeat": True},
-         {"properties": [("level", -1), ("relative", True)]}),
+         {"properties": [("level", -1), ("relative", True), ("ensure_modifier", False)]}),
         # Mask
         ("paint.mask_flood_fill", {"type": 'A', "value": 'PRESS', "ctrl": True, "shift": True},
          {"properties": [("mode", 'VALUE'), ("value", 1.0)]}),

scripts/startup/bl_operators/object.py

@@ -230,6 +230,12 @@ class SubdivisionSet(Operator):
         description="Apply the subdivision surface level as an offset relative to the current level",
         default=False,
     )
+    ensure_modifier: BoolProperty(
+        name="Ensure Modifier",
+        description="Create the corresponding modifier if it does not exist",
+        default=True,
+        options={'HIDDEN'}
+    )
 
     @classmethod
     def poll(cls, context):
@@ -239,10 +245,30 @@ class SubdivisionSet(Operator):
     def execute(self, context):
         level = self.level
         relative = self.relative
+        ensure_modifier = self.ensure_modifier
 
         if relative and level == 0:
             return {'CANCELLED'}  # nothing to do
 
+        if not ensure_modifier:
+            any_object_has_relevant_modifier = False
+            for obj in context.selected_editable_objects:
+                if obj.mode == 'SCULPT':
+                    any_object_has_relevant_modifier |= any(mod.type == 'MULTIRES' for mod in obj.modifiers)
+                elif obj.mode == 'OBJECT':
+                    any_object_has_relevant_modifier |= any(mod.type == 'SUBSURF' for mod in obj.modifiers)
+                if any_object_has_relevant_modifier:
+                    break
+
+            if not any_object_has_relevant_modifier:
+                mod_name = ""
+                if obj.mode == 'SCULPT':
+                    mod_name = "Multiresolution"
+                else:
+                    mod_name = "Subdivision Surface"
+                self.report({'WARNING'}, "No {0} modifiers found".format(mod_name))
+                return {'CANCELLED'}
+
         if not relative and level < 0:
             self.level = level = 0
 
@@ -281,17 +307,18 @@ class SubdivisionSet(Operator):
                     return
 
             # add a new modifier
-            try:
-                if obj.mode == 'SCULPT':
-                    mod = obj.modifiers.new("Multires", 'MULTIRES')
-                    if level > 0:
-                        for _ in range(level):
-                            bpy.ops.object.multires_subdivide(modifier="Multires")
-                else:
-                    mod = obj.modifiers.new("Subdivision", 'SUBSURF')
-                    mod.levels = level
-            except Exception:
-                self.report({'WARNING'}, "Modifiers cannot be added to object: " + obj.name)
+            if ensure_modifier:
+                try:
+                    if obj.mode == 'SCULPT':
+                        mod = obj.modifiers.new("Multires", 'MULTIRES')
+                        if level > 0:
+                            for _ in range(level):
+                                bpy.ops.object.multires_subdivide(modifier="Multires")
+                    else:
+                        mod = obj.modifiers.new("Subdivision", 'SUBSURF')
+                        mod.levels = level
+                except Exception:
+                    self.report({'WARNING'}, "Modifiers cannot be added to object: " + obj.name)
 
         for obj in context.selected_editable_objects:
             set_object_subd(obj)