FBX to C3X resulting in 1KB files

So recently I was asked by a friend to convert a few FBX files to C3X/CoCos format for a game he’s developing. Seemed simple enough but kept resulting in 1KB files!

Quickly researching the task seemed simple enough, someone had already written and compiled a windows binary for it: https://github.com/cocos2d/cocos2d-x-3rd-party-libs-bin/tree/v3/fbx-conv

So downloaded binary, downloaded FBX file, ran with the -a switch and done!

D:\Data\Downloads\FBX\fbx>fbx-conv.exe -a "Dragon 2.5_fbx.fbx"
 INFO:     FBX to c3x converter, version 0.7 x32 (release version, cocos2d-x-3.4-beta0 or later version can use)
 STATUS:   Loading source file
 WARNING:  Mesh contains more indices (113958) than the specified maximum (32767)
 STATUS:   Converting source file
 STATUS:   Closing source file
 STATUS:   Exporting to c3t file: Dragon 2.5_fbx.c3t
 STATUS:   Exporting to c3b file: Dragon 2.5_fbx.c3b
 STATUS:   Closing exported file

This was only a test file so I could safely ignore the mesh indices being too large. So off I went, downloaded all the FBX assets he’d purchased and converted them all. Sent them across to him, only to get a message an hour later saying the dev says they’re all empty! Checking the files I’d sent him indeed shows they’re 1KB!

Crystals C3X Files

They were small files to convert so I expected the output to be tiny but 1KB is definitely too small. Running it with verbose enabled shows a bit more of the story: Check out the below output and see if you can spot it:

D:\Data\Downloads\FBX\drive-download-20190328T192009Z-001\Hex_Crystal>fbx-conv.exe -v -a Base_low.fbx
 INFO:     FBX to c3x converter, version 0.7 x32 (release version, cocos2d-x-3.4-beta0 or later version can use)
 STATUS:   Loading source file
 PROGRESS: Import FBX 100.00%
 STATUS:   Converting source file
 STATUS:   Closing source file
 VERBOSE:  Listing model information:
 VERBOSE:  ID        :
 VERBOSE:  Version   : Hi=0, Lo=7
 VERBOSE:  Meshes    : 0 (0 vertices, 0 parts, 0 indices)
 VERBOSE:  Nodes     : 0 root, 0 total, 0 parts
 VERBOSE:  Materials : 0 (0 textures)
 STATUS:   Exporting to c3t file: Base_low.c3t
 STATUS:   Exporting to c3b file: Base_low.c3b
 STATUS:   Closing exported file

Yep, that’s right. 0 meshes, 0 nodes and no mention of polygons or indices!

Obviously needing to dig further I downloaded and installed Autodesk FBX Review to see them (https://apps.autodesk.com/MAYA/en/Detail/Index?id=6979630331069053932&appLang=en&os=Win64) and opened the files.

Dragon FBX
Crystals FBX

Both loading and rendering fine. Sure the scale is way off but the crystal towers certainly have more than 0 nodes. So logically it must be the tool used.

Onto the next step – can I convert it into anything? Lets try the official Autodesk FBX Converter (https://www.autodesk.com/developer-network/platform-technologies/fbx-converter-archives). Sure it can’t do C3X but the objective now is just to see if it works.

Failed Convert

Typical. Dragon works and Crystal doesn’t! However this seems to give a bit more information – “Not enough parameters” and no creator! Back to google it is!

Eventually after a fair bit of digging, downloading random FBX assets and trying to convert them I eventually found the issue – any assets made after 2016 don’t work.

Bit more digging and found the AutoDesk Changelog document – https://help.autodesk.com/view/FBX/2017/ENU/?guid=__files_GUID_2ADB9BCE_15EA_485F_87C2_32D43F2D219D_htm
Specifically note the 2016 second point: “Updated the FBX file format to 7.5. This new file format is only compatible with the 2016 or later product versions that use 64-bit integers in the binary block headers for large file support (> 2GB).

There we go! New files are completely different, which explains why the old Autodesk tool converter didn’t work either. As a test I then downloaded a trial of Autodesk Maya, opened the original FBX file, saved as 2014-2015 version and then ran the FBX to C3X.

D:\Data\Downloads\FBX\drive-download-20190328T192009Z-001\Hex_Crystal>fbx-conv.exe -v -a Base_low_1.fbx
 INFO:     FBX to c3x converter, version 0.7 x32 (release version, cocos2d-x-3.4-beta0 or later version can use)
 STATUS:   Loading source file
 PROGRESS: Import FBX 100.00%
 STATUS:   [shape(Base_low)] Triangulating FbxMesh geometry
 VERBOSE:  [shape(Crystal_low)] polygons: 32 (96 indices), control points: 20
 VERBOSE:  [shape(Base_low)] polygons: 48 (144 indices), control points: 30
 STATUS:   Converting source file
 STATUS:   Closing source file
 VERBOSE:  Listing model information:
 VERBOSE:  ID        :
 VERBOSE:  Version   : Hi=0, Lo=7
 VERBOSE:  Meshes    : 1 (496 vertices, 2 parts, 240 indices)
 VERBOSE:  Nodes     : 2 root, 2 total, 2 parts
 VERBOSE:  Materials : 1 (0 textures)
 STATUS:   Exporting to c3t file: Base_low_1.c3t
 STATUS:   Exporting to c3b file: Base_low_1.c3b
 STATUS:   Closing exported file

Finally got there; we have meshes, nodes, indices and more importantly a 4KB C3B file and a 9KB C3T! The artist has now been requested to save them in this format and my friend is happily converting them as and when he needs.

TLDR: New FBX + old C3X = bad. If you want to convert FBX to C3X using the CLI tool then save your FBX as versions prior to 2016!

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