Preferences: Customize default empty size for collection instances

The old value (1.0) was often too large in practice. When many collection
instances are created, the large empties create a mess in the viewport.

This adds a new preference setting in `Editing -> Objects -> New Objects`
called `Instance Empty Size`.

The value will be used as display size for new empties containing a
collection instance.

Reviewers: Severin

Differential Revision: https://developer.blender.org/D7650

release/datafiles/userdef/userdef_default.c

@@ -227,6 +227,8 @@ const UserDef U_default = {
     .sequencer_disk_cache_size_limit = 100,
     .sequencer_disk_cache_flag = 0,
 
+    .collection_instance_empty_size = 1.0f,
+
     .runtime =
         {
             .is_dirty = 0,

release/scripts/startup/bl_ui/space_userpref.py

@@ -360,6 +360,7 @@ class USERPREF_PT_edit_objects_new(EditingPanel, CenterAlignMixIn, Panel):
         flow.prop(edit, "material_link", text="Link Materials to")
         flow.prop(edit, "object_align", text="Align to")
         flow.prop(edit, "use_enter_edit_mode", text="Enter Edit Mode")
+        flow.prop(edit, "collection_instance_empty_size", text="Instance Empty Size")
 
 
 class USERPREF_PT_edit_objects_duplicate_data(EditingPanel, CenterAlignMixIn, Panel):

source/blender/blenloader/intern/readfile.c

@@ -11942,6 +11942,7 @@ static void add_collections_to_scene(Main *mainvar,
       /* BKE_object_add(...) messes with the selection. */
       Object *ob = BKE_object_add_only_object(bmain, OB_EMPTY, collection->id.name + 2);
       ob->type = OB_EMPTY;
+      ob->empty_drawsize = U.collection_instance_empty_size;
 
       BKE_collection_object_add(bmain, active_collection, ob);
       Base *base = BKE_view_layer_base_find(view_layer, ob);

source/blender/blenloader/intern/versioning_userdef.c

@@ -764,6 +764,10 @@ void BLO_version_defaults_userpref_blend(Main *bmain, UserDef *userdef)
    */
   {
     /* Keep this block, even when empty. */
+
+    if (userdef->collection_instance_empty_size == 0) {
+      userdef->collection_instance_empty_size = 1.0f;
+    }
   }
 
   if (userdef->pixelsize == 0.0f) {

source/blender/editors/object/object_add.c

@@ -1357,6 +1357,7 @@ static int collection_instance_add_exec(bContext *C, wmOperator *op)
     Object *ob = ED_object_add_type(
         C, OB_EMPTY, collection->id.name + 2, loc, rot, false, local_view_bits);
     ob->instance_collection = collection;
+    ob->empty_drawsize = U.collection_instance_empty_size;
     ob->transflag |= OB_DUPLICOLLECTION;
     id_us_plus(&collection->id);
 

source/blender/makesdna/DNA_userdef_types.h

@@ -873,9 +873,11 @@ typedef struct UserDef {
   int sequencer_disk_cache_compression; /* eUserpref_DiskCacheCompression */
   int sequencer_disk_cache_size_limit;
   short sequencer_disk_cache_flag;
-
   char _pad5[2];
 
+  float collection_instance_empty_size;
+  char _pad10[4];
+
   struct WalkNavigation walk_navigation;
 
   /** The UI for the user preferences. */

source/blender/makesrna/intern/rna_userdef.c

@@ -4840,6 +4840,12 @@ static void rna_def_userdef_edit(BlenderRNA *brna)
   RNA_def_property_ui_text(
       prop, "Enter Edit Mode", "Enter Edit Mode automatically after adding a new object");
 
+  prop = RNA_def_property(srna, "collection_instance_empty_size", PROP_FLOAT, PROP_NONE);
+  RNA_def_property_range(prop, 0.001f, FLT_MAX);
+  RNA_def_property_ui_text(prop,
+                           "Collection Instance Empty Size",
+                           "Display size of the empty when new collection instances are created");
+
   /* Undo */
 
   prop = RNA_def_property(srna, "undo_steps", PROP_INT, PROP_NONE);