Fix T70298: FBX IO: Apply squared crease transform when importing/exporting.

Blender maps crease sharpness from internal [0, 1] to OpenSubdiv's
[0, 10] by squaring the value (see `get_edge_sharpness()`).

Other software seems to treat FBX crease as linear times 10 using OpenSubdiv.

This commits attempts to make FBX exported by Blender consistent with the
results from FBX exported from Maya regarding crease intensity.

Differential Revision: https://developer.blender.org/D5930

io_scene_fbx/__init__.py

@@ -21,7 +21,7 @@
 bl_info = {
     "name": "FBX format",
     "author": "Campbell Barton, Bastien Montagne, Jens Restemeier",
-    "version": (4, 17, 2),
+    "version": (4, 17, 3),
     "blender": (2, 81, 6),
     "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

@@ -1010,7 +1010,9 @@ def fbx_data_mesh_elements(root, me_obj, scene_data, done_meshes):
         for e in me.edges:
             if e.key not in edges_map:
                 continue  # Only loose edges, in theory!
-            t_ec[edges_map[e.key]] = e.crease
+            # Blender squares those values before sending them to OpenSubdiv, when other softwares don't,
+            # so we need to compensate that to get similar results through FBX...
+            t_ec[edges_map[e.key]] = e.crease * e.crease
 
         lay_crease = elem_data_single_int32(geom, b"LayerElementEdgeCrease", 0)
         elem_data_single_int32(lay_crease, b"Version", FBX_GEOMETRY_CREASE_VERSION)

io_scene_fbx/import_fbx.py

@@ -1117,6 +1117,8 @@ def blen_read_geom_layer_smooth(fbx_obj, mesh):
         return False
 
 def blen_read_geom_layer_edge_crease(fbx_obj, mesh):
+    from math import sqrt
+
     fbx_layer = elem_find_first(fbx_obj, b'LayerElementEdgeCrease')
 
     if fbx_layer is None:
@@ -1151,6 +1153,9 @@ def blen_read_geom_layer_edge_crease(fbx_obj, mesh):
             fbx_layer_data, None,
             fbx_layer_mapping, fbx_layer_ref,
             1, 1, layer_id,
+            # Blender squares those values before sending them to OpenSubdiv, when other softwares don't,
+            # so we need to compensate that to get similar results through FBX...
+            xform=sqrt,
             )
     else:
         print("warning layer %r mapping type unsupported: %r" % (fbx_layer.id, fbx_layer_mapping))