FBX: enable import of 7500 (FBX2016) files.

Looks like only change here was that binary switch from uint32 to uint64
for some core metadata of the format. At leas, could import some 7500
files here with that mere change.

Thanks again @xchip (Raul Aguaviva) for finding the culprit in T49822!

io_scene_fbx/fbx2json.py

@@ -88,9 +88,11 @@ del namedtuple
 def read_uint(read):
     return unpack(b'<I', read(4))[0]
 
+
 def read_uint64(read):
     return unpack(b'<Q', read(8))[0]
 
+
 def read_ubyte(read):
     return unpack(b'B', read(1))[0]
 

io_scene_fbx/parse_fbx.py

@@ -36,9 +36,9 @@ from . import data_types
 
 # at the end of each nested block, there is a NUL record to indicate
 # that the sub-scope exists (i.e. to distinguish between P: and P : {})
-# this NUL record is 13 bytes long.
-_BLOCK_SENTINEL_LENGTH = 13
-_BLOCK_SENTINEL_DATA = (b'\0' * _BLOCK_SENTINEL_LENGTH)
+_BLOCK_SENTINEL_LENGTH = ...
+_BLOCK_SENTINEL_DATA = ...
+read_fbx_elem_uint = ...
 _IS_BIG_ENDIAN = (__import__("sys").byteorder != 'little')
 _HEAD_MAGIC = b'Kaydara FBX Binary\x20\x20\x00\x1a\x00'
 from collections import namedtuple
@@ -50,6 +50,10 @@ def read_uint(read):
     return unpack(b'<I', read(4))[0]
 
 
+def read_uint64(read):
+    return unpack(b'<Q', read(8))[0]
+
+
 def read_ubyte(read):
     return unpack(b'B', read(1))[0]
 
@@ -98,16 +102,34 @@ read_data_dict = {
     }
 
 
+# FBX 7500 (aka FBX2016) introduces incompatible changes at binary level:
+#   * The NULL block marking end of nested stuff switches from 13 bytes long to 25 bytes long.
+#   * The FBX element metadata (end_offset, prop_count and prop_length) switch from uint32 to uint64.
+def init_version(fbx_version):
+    global _BLOCK_SENTINEL_LENGTH, _BLOCK_SENTINEL_DATA, read_fbx_elem_uint
+
+    assert(_BLOCK_SENTINEL_LENGTH == ...)
+    assert(_BLOCK_SENTINEL_DATA == ...)
+
+    if fbx_version < 7500:
+        _BLOCK_SENTINEL_LENGTH = 13
+        read_fbx_elem_uint = read_uint
+    else:
+        _BLOCK_SENTINEL_LENGTH = 25
+        read_fbx_elem_uint = read_uint64
+    _BLOCK_SENTINEL_DATA = (b'\0' * _BLOCK_SENTINEL_LENGTH)
+
+
 def read_elem(read, tell, use_namedtuple):
     # [0] the offset at which this block ends
     # [1] the number of properties in the scope
     # [2] the length of the property list
-    end_offset = read_uint(read)
+    end_offset = read_fbx_elem_uint(read)
     if end_offset == 0:
         return None
 
-    prop_count = read_uint(read)
-    prop_length = read_uint(read)
+    prop_count = read_fbx_elem_uint(read)
+    prop_length = read_fbx_elem_uint(read)
 
     elem_id = read_string_ubyte(read)        # elem name of the scope/key
     elem_props_type = bytearray(prop_count)  # elem property types
@@ -159,8 +181,7 @@ def parse(fn, use_namedtuple=True):
             raise IOError("Invalid header")
 
         fbx_version = read_uint(read)
-        if fbx_version >= 7500:
-            raise IOError("Unsupported FBX version (%d), binary format is incompatible!" % fbx_version)
+        init_version(fbx_version)
 
         while True:
             elem = read_elem(read, tell, use_namedtuple)