Fix T39897: shape keys created while the Relative checkbox is unchecked start out with frame=0

So! First, frame for absolute shape keys: never allow a new key to have the same pos as an
existing one (this does not make sense). This way, the two workflows are possible (create
all keys and then animate ctime, or animate ctime and then create keys where you need them).

Also, fixed UIList for shapekeys, the "absolute" test was wrong, and better to show frame
value, even though not editable, than nothing in case of absolute keys.

And finally, add getter to RNA 'frame' readonly value, so that we output real frame values,
and not dummy internal ones (which are /100) in our API.

release/scripts/startup/bl_ui/properties_data_mesh.py

@@ -61,7 +61,7 @@ class MESH_MT_shape_key_specials(Menu):
 
 class MESH_UL_vgroups(UIList):
     def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
-        # assert(isinstance(item, bpy.types.VertexGroup)
+        # assert(isinstance(item, bpy.types.VertexGroup))
         vgroup = item
         if self.layout_type in {'DEFAULT', 'COMPACT'}:
             layout.prop(vgroup, "name", text="", emboss=False, icon_value=icon)
@@ -74,7 +74,7 @@ class MESH_UL_vgroups(UIList):
 
 class MESH_UL_shape_keys(UIList):
     def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
-        # assert(isinstance(item, bpy.types.ShapeKey)
+        # assert(isinstance(item, bpy.types.ShapeKey))
         obj = active_data
         # key = data
         key_block = item
@@ -84,7 +84,9 @@ class MESH_UL_shape_keys(UIList):
             row = split.row(align=True)
             if key_block.mute or (obj.mode == 'EDIT' and not (obj.use_shape_key_edit_mode and obj.type == 'MESH')):
                 row.active = False
-            if not item.relative_key or index > 0:
+            if not item.id_data.use_relative:
+                row.prop(key_block, "frame", text="", emboss=False)
+            elif index > 0:
                 row.prop(key_block, "value", text="", emboss=False)
             else:
                 row.label(text="")
@@ -96,7 +98,7 @@ class MESH_UL_shape_keys(UIList):
 
 class MESH_UL_uvmaps_vcols(UIList):
     def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
-        # assert(isinstance(item, (bpy.types.MeshTexturePolyLayer, bpy.types.MeshLoopColorLayer))
+        # assert(isinstance(item, (bpy.types.MeshTexturePolyLayer, bpy.types.MeshLoopColorLayer)))
         if self.layout_type in {'DEFAULT', 'COMPACT'}:
             layout.prop(item, "name", text="", emboss=False, icon_value=icon)
             icon = 'RESTRICT_RENDER_OFF' if item.active_render else 'RESTRICT_RENDER_ON'

source/blender/blenkernel/intern/key.c

@@ -1558,9 +1558,23 @@ KeyBlock *BKE_keyblock_add(Key *key, const char *name)
 KeyBlock *BKE_keyblock_add_ctime(Key *key, const char *name, const bool do_force)
 {
 	KeyBlock *kb = BKE_keyblock_add(key, name);
+	const float cpos = key->ctime / 100.0f;
 
+	/* In case of absolute keys, there is no point in adding more than one key with the same pos.
+	 * Hence only set new keybloc pos to current time if none previous one already use it.
+	 * Now at least people just adding absolute keys without touching to ctime
+	 * won't have to systematically use retiming func (and have ordering issues, too). See T39897.
+	 */
+	if (!do_force && (key->type != KEY_RELATIVE)) {
+		KeyBlock *it_kb;
+		for (it_kb = key->block.first; it_kb; it_kb = it_kb->next) {
+			if (it_kb->pos == cpos) {
+				return kb;
+			}
+		}
+	}
 	if (do_force || (key->type != KEY_RELATIVE)) {
-		kb->pos = key->ctime / 100.0f;
+		kb->pos = cpos;
 		BKE_key_sort(key);
 	}
 

source/blender/editors/object/object_shapekey.c

@@ -334,7 +334,7 @@ void OBJECT_OT_shape_key_add(wmOperatorType *ot)
 	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
 
 	/* properties */
-	RNA_def_boolean(ot->srna, "from_mix", 1, "From Mix", "Create the new shape key from the existing mix of keys");
+	RNA_def_boolean(ot->srna, "from_mix", true, "From Mix", "Create the new shape key from the existing mix of keys");
 }
 
 static int shape_key_remove_exec(bContext *C, wmOperator *op)

source/blender/makesrna/intern/rna_key.c

@@ -92,6 +92,12 @@ static void rna_ShapeKey_name_set(PointerRNA *ptr, const char *value)
 	BKE_all_animdata_fix_paths_rename(NULL, "key_blocks", oldname, kb->name);
 }
 
+static float rna_ShapeKey_frame_get(PointerRNA *ptr)
+{
+	KeyBlock *kb = (KeyBlock *)ptr->data;
+	return kb->pos * 100.0f;  /* Because pos is ctime/100... */
+}
+
 static void rna_ShapeKey_value_set(PointerRNA *ptr, float value)
 {
 	KeyBlock *data = (KeyBlock *)ptr->data;
@@ -571,6 +577,7 @@ static void rna_def_keyblock(BlenderRNA *brna)
 	prop = RNA_def_property(srna, "frame", PROP_FLOAT, PROP_TIME);
 	RNA_def_property_clear_flag(prop, PROP_EDITABLE);
 	RNA_def_property_float_sdna(prop, NULL, "pos");
+	RNA_def_property_float_funcs(prop, "rna_ShapeKey_frame_get", NULL, NULL);
 	RNA_def_property_ui_text(prop, "Frame", "Frame for absolute keys");
 	RNA_def_property_update(prop, 0, "rna_Key_update_data");