Assets

Assets

TressFX uses three file types. AMD's Maya exporter and this addon's Blender exporter write all three; the Maya ASCII converter writes the first.

.tfx: the guide strands

A binary file (TressFX file format version 4) with a 160-byte header followed by the vertices:

• number of strands and vertices per strand;
• for every vertex a float4: x, y, z and an inverse mass in w. w = 0 pins the vertex (the first two vertices of every strand are pinned to the scalp), w = 1 lets it move;
• optionally one float2 per strand, the texture coordinate on the body used to colour the strand from the body's albedo texture.

Rules the addon enforces on load:

• Vertices per strand must be 4, 8, 16, 32 or 64. 16 suits most hair, 8 is enough for short fur, 32 for long hair with curls.
• The strand count is padded up to a multiple of 64 (the compute thread group size); padding strands are copies of the last real strand and cost almost nothing.
• Positions are in metres. For an asset authored in centimetres set import_scale to 0.01 on the node; the positions are scaled on load, before the follow hairs are generated.
• At most 16 million vertices per node.

.tfxbone: skinning weights

For every guide strand, four bone indices and four weights, plus the list of bone names. On load each name is looked up in the node's hair_skeleton with Skeleton3D.find_bone(), so the names in the file must match the names in the imported skeleton exactly. A missing bone prints a warning and falls back to bone 0.

Without a .tfxbone (or without a skeleton) the whole hairstyle is attached to a single transform: the node's own.

.tfxmesh: a collision mesh

A text file with bone names, then vertices (position, normal, four bone indices, four weights), then triangles. TressFXCollisionMesh reads it directly; a bone name runs to the end of its line. You do not need this format: any Godot Mesh works as a collider, and primitives (CapsuleMesh, SphereMesh) are usually better than a real body mesh because they are closed and smooth. Its use is a low-poly body proxy skinned like the character, which the Blender exporter writes from any mesh marked as a collider.

Producing the files

Maya

AMD ships a Maya exporter with TressFX (tool/Maya in the TressFX repository). It writes all three formats from a groom made of curves and a skinned mesh.

Maya ASCII curves without Maya

addons/tressfx/tools/ma_to_tfx.py reads every nurbsCurve from a .ma file, resamples each curve by arc length and writes a .tfx (no strand UVs, no bones):

python3 addons/tressfx/tools/ma_to_tfx.py hair.ma hair.tfx 16
python3 addons/tressfx/tools/ma_to_tfx.py hair.ma hair.tfx 16 --split-tail-z=-2.5

The third argument is the vertices per strand. --split-tail-z writes two files, hair_head.tfx and hair_tail.tfx: strands whose tip lies below the given z go to the tail. That is how the ponytail demo gets a stiff scalp part and a loose tail, each with its own node and settings. Units are kept as they are in the file; set import_scale on the node.

Blender

addons/tressfx/tools/tressfx_blender_export.py is the Blender to Godot Hair add-on (Blender 4.2 or later) that writes the .tfx with strand UVs and the .tfxbone from a hair Curves object and its skinned surface mesh, and a .tfxmesh from every mesh marked as a hair collider. Hair from Blender walks through grooming, exporting and the Godot setup.

Writing your own

The format is small enough to write from any tool, including a Godot script. The header is:

Offset	Type	Field
0	float	version, write 4.0
4	uint32	number of strands
8	uint32	vertices per strand
12	uint32	offset of the vertex positions, 160
16	uint32	offset of the strand UVs, 0 if none
20	3 x uint32	reserved, 0
32	32 x uint32	reserved, 0

followed at offset 160 by strands * vertices_per_strand float4 values. Make the first two vertices of every strand w = 0 and the rest w = 1.

One hairstyle, several parts

TressFX 4 has no per-strand parameter groups: every strand in a node shares the same stiffness, damping and gravity. A hairstyle whose parts must behave differently (a stiff scalp and a loose tail, bangs and a mane) is split into several .tfx files, one TressFXHair node each. All of them can share the same colliders and the same material settings.