About

FBX (Filmbox) is Autodesk's proprietary 3D interchange format used across most DCC tools (Blender, Maya, 3ds Max). LibGDX, the Java game framework, uses its own binary format G3DB (and its JSON sibling G3DJ) for runtime model loading. The official fbx-conv command-line tool requires a native binary per OS and a local build environment. Getting the conversion wrong produces invisible models, flipped faces, or corrupted UV maps that waste hours of debugging. This tool parses real FBX 7.x binary data in your browser, extracts geometry nodes (vertices, polygon vertex indices, normals, UV layers), applies optional UV coordinate flipping (v → 1 − v) to correct Blender's inverted texture coordinates, and serializes valid G3DB or G3DJ output. Limitations: this handles static meshes. Skeletal animation, blend shapes, and embedded textures require the native fbx-conv binary.

Formulas

FBX binary stores polygon indices using a sign convention. Each polygon's last index is stored as a bitwise negation to mark the polygon boundary:

actual_index = ¬raw_index (i.e., −raw_index − 1) when raw_index < 0

N-gon triangulation uses fan decomposition from vertex v₀:

For polygon [v₀, v₁, … v_n] → triangles: (v₀, v_i, v_i+1) for i = 1 … n−1

UV coordinate flipping corrects Blender's inverted V-axis:

v_corrected = 1.0 − v_original

G3DB vertex stride is determined by enabled attributes:

stride = 3 (position) + 3 (normal) + 2 (texcoord) = 8 floats/vertex

Where v₀ through v_n are polygon vertex indices, v_corrected is the flipped texture V coordinate, and stride is the number of float components per interleaved vertex.

Reference Data

Feature	FBX Binary 7.x	G3DJ (JSON)	G3DB (Binary)
Format Type	Binary (proprietary)	JSON text	Binary (LE)
Magic Bytes	`Kaydara FBX Binary`	N/A (JSON)	N/A (G3DJ binary form)
Vertex Positions	Vertices in Geometry node	`meshes[].vertices[]`	Float32 array
Normals	LayerElementNormal	`attributes["NORMAL"]`	Float32 interleaved
UV Coordinates	LayerElementUV	`attributes["TEXCOORD0"]`	Float32 interleaved
Indices	PolygonVertexIndex (negative = end)	`parts[].indices[]`	Int16/Int32 array
Materials	Material node properties	`materials[]` with colors	Serialized material block
Transforms	Model node Lcl props	`nodes[].translation/rotation/scale`	Float32 arrays
Animation	AnimationCurveNode	`animations[]`	Keyframe blocks
Max Vertices (typical)	Unlimited	~65535 per mesh part	~65535 (short indices)
Endianness	Little-endian	N/A	Little-endian
String Encoding	Length-prefixed	UTF-8	Length-prefixed UTF-8
Compression	Optional zlib per node (7.5+)	None	None
File Extension	`.fbx`	`.g3dj`	`.g3db`
Human Readable	No	Yes	No
LibGDX Loader	Not supported	`G3dModelLoader`	`G3dModelLoader`
UV Flip Needed (Blender)	Yes (V axis)	Applied during conversion	Applied during conversion
Polygon Support	N-gons, Tris, Quads	Triangles only	Triangles only
Typical File Size Ratio	1.0×	~3−5× larger	~0.3−0.5×

Frequently Asked Questions

Blender and most DCC tools use a bottom-left UV origin, while LibGDX (OpenGL) expects top-left for standard texture sampling. Enable the "Flip UVs" option to apply v → 1.0 − v correction. The original fbx-conv tool defaults this to true for the same reason.

This tool parses FBX Binary format version 7.x (versions 7100 through 7700), which covers exports from Blender 2.8+, Maya 2015+, and 3ds Max 2015+. FBX ASCII format and versions below 7000 are not supported. Check your export settings to ensure "FBX Binary" is selected.

Use G3DB for production builds. It is the binary-serialized form of G3DJ, typically 60−70% smaller and faster to parse at runtime. Use G3DJ (JSON) during development for debugging - you can open it in a text editor and inspect vertex data, material assignments, and node hierarchy directly.

FBX supports arbitrary polygons. LibGDX requires triangulated meshes. The converter automatically performs fan triangulation: for a polygon with vertices [v₀, v₁, ..., v_n], it generates triangles (v₀, v_i, v_i+1). For complex concave n-gons, pre-triangulate in your modeling software for best results.

The tool processes files up to 100 MB. Processing occurs in a Web Worker to avoid blocking the UI. A model with 500,000 triangles typically converts in under 3 seconds on modern hardware. Memory usage is approximately 3× the input file size during peak conversion.

No. This converter extracts static mesh geometry (positions, normals, UVs) and basic material properties. Skeletal animation requires parsing FBX AnimationCurveNode trees and deformer clusters, which demands the native fbx-conv binary. For animated models, use the command-line tool from libgdx.badlogicgames.com/fbx-conv/.