Fbx IO: improve export speed of 'rested' armatures

As part of Fbx Export, while handling Armature modifiers for Meshes, each
armature's position is backed up, then put into REST position for exporting,
and then restored back to original position. A dependency graph update is
triggered at the end of this.

This commit avoids the whole backing position setting + depsgraph update in
case the armature is already in rest position.

As an example, a model which I am developing for a game used to take
20 minutes for the Fbx Export. After this change, it only takes 20 seconds.

Reviewed By: mont29

Differential Revision: https://developer.blender.org/D13712

io_scene_fbx/__init__.py

@@ -21,7 +21,7 @@
 bl_info = {
     "name": "FBX format",
     "author": "Campbell Barton, Bastien Montagne, Jens Restemeier",
-    "version": (4, 27, 0),
+    "version": (4, 28, 0),
     "blender": (2, 90, 0),
     "location": "File > Import-Export",
     "description": "FBX IO meshes, UV's, vertex colors, materials, textures, cameras, lamps and actions",

io_scene_fbx/export_fbx_bin.py

@@ -2287,8 +2287,12 @@ def fbx_data_from_scene(scene, depsgraph, settings):
                         object = mod.object
                         if object and object.type == 'ARMATURE':
                             armature = object.data
-                            backup_pose_positions.append((armature, armature.pose_position))
-                            armature.pose_position = 'REST'
+                            # If armature is already in REST position, there's nothing to back-up
+                            # This cuts down on export time dramatically, if all armatures are already in REST position
+                            # by not triggering dependency graph update
+                            if armature.pose_position != 'REST':
+                                backup_pose_positions.append((armature, armature.pose_position))
+                                armature.pose_position = 'REST'
                     elif mod.show_render or mod.show_viewport:
                         # If exporting with subsurf collect the last Catmull-Clark subsurf modifier
                         # and disable it. We can use the original data as long as this is the first