Vertex animation textures (VAT)

A vertex animation texture (VAT) stores an animation or simulation as pixels: each pixel holds where one vertex should be in one frame, and a vertex shader reads those pixels to move a static mesh. SideFX describes its VAT exporter as a tool for "complex real-time effects" such as soft-body deformation, rigid-body dynamics, remeshed fluids and particle sprites (Houdini documentation: Labs Vertex Animation Textures 3.0 render node).

Because the motion lives in textures and the shader, the engine treats the mesh as static. SideFX notes this gives a lighter CPU cost than skeletal animation (Houdini documentation: Labs Vertex Animation Textures 3.0 render node), and Pingle Studio's head of technical art puts it as "for the CPU, such geometry is perceived as completely static" (Pingle Studio blog: How to Breathe Life into Your Game Characters…).

#How the data is laid out

The exporter writes the mesh once and one or more textures beside it. In the simplest layout, every vertex gets a column and every frame a row; the pixel colour stores the vertex position as RGB. Blender's OpenVAT add-on writes positions (and optionally normals) into image pixels frame by frame and saves a JSON file with "min/max per channel for accurate reconstruction", because colour values must be remapped back into real positions (Blender Extensions: OpenVAT).

Houdini's Labs VAT 3.0 node offers four modes, each with different textures (Houdini documentation: Labs Vertex Animation Textures 3.0 render node):

Precision matters. SideFX recommends HDR textures "if your performance budget can afford it", and offers to split positions across two 8-bit textures when an engine lacks 16- or 32-bit support (Houdini documentation: Labs Vertex Animation Textures 3.0 render node). OpenVAT exports "16-bit PNG or EXR (half-float)" (Blender Extensions: OpenVAT).

#What VATs are used for

• Crowds. Baking character animation clips into textures lets thousands of instanced meshes animate without skeletal-mesh cost. Mohamad Salame of SuperNatural Studios presents baking Houdini KineFX crowd animation into VATs played back with World Position Offset in Unreal (SideFX talks: Vertex Animation Textures for Crowds). Isaac Oster built an ambient zombie crowd in Unreal 5 from Mixamo animations converted with the AnimToTexture plugin and driven by Niagara (ArtStation: Zombie Horde with Vertex Animated Textures…).
• Destruction and shattering. Rigid-body mode exports packed pieces and their transforms (Houdini documentation: Labs Vertex Animation Textures 3.0 render node), so a building collapse simulated offline plays back as one static mesh.
• Liquids and morphing. For changing shapes, Pingle notes that a "skeletal rig wouldn't work at all" (Pingle Studio blog: How to Breathe Life into Your Game Characters…); fluid mode handles topology that changes every frame (Houdini documentation: Labs Vertex Animation Textures 3.0 render node).
• Cloth and flags. Soft-body mode keeps topology fixed and moves vertices, which suits flags, banners and curtains (Houdini documentation: Labs Vertex Animation Textures 3.0 render node). For simple looping wind on foliage, a procedural shader is usually enough; see wind and world position offset.

#How to make one

Houdini (Labs VAT 3.0) to Unreal or Unity

1. Build or simulate the effect, for example an RBD fracture of a wall, and cache it.
2. Add a Labs Vertex Animation Textures ROP. Set Mode (Rigid for the wall), Target Engine, the Start/End frames and the input geometry, and check the Input tab requirements for that mode (Houdini documentation: Labs Vertex Animation Textures 3.0 render node).
3. Choose texture format: HDR if the budget allows; for rigid bodies, SideFX recommends Very High pivot accuracy (Houdini documentation: Labs Vertex Animation Textures 3.0 render node).
4. Set the export path and asset name and press Render All. In Fluid mode, render the First Pass, then switch to Second Pass and render again (Houdini documentation: Labs Vertex Animation Textures 3.0 render node).
5. Import the mesh and textures into the engine and use the matching shaders from the node's Real-Time Shaders section or its "Unreal Engine Plugin and Guides" button (Houdini documentation: Labs Vertex Animation Textures 3.0 render node; SideFX tutorials: Vertex Animation Textures in Unreal). SideFX's Soft-Body mode needs only "a single FBX file, a single material, and a single set of textures" (80 Level: A Complete Guide on SideFX's Vertex Animation…).
6. Scrub the material's time or frame parameter and compare against the Houdini playback. Users on SideFX's tutorial page report fixing flicker in UE5 by enabling full-precision UVs on the static mesh and disabling Nanite for it (SideFX tutorials: Vertex Animation Textures in Unreal); treat this as community advice.

Blender (OpenVAT)

1. Install OpenVAT (Blender 4.2 LTS or newer) from Preferences (Blender Extensions: OpenVAT).
2. Select the animated mesh or collection and choose an encoding type, frame range, normal packing and output formats (Blender Extensions: OpenVAT).
3. Click Encode Vertex Animation Texture; a preview object appears that you can scrub to check the result (Blender Extensions: OpenVAT).
4. In Unity, install the OpenVAT package and use Tools > OpenVAT to set up materials and prefabs; set texture compression to RGB 16 or Automatic and match the max size to the exported dimensions (Blender Extensions: OpenVAT).
5. In Unreal 5, import the textures with RGB16 compression; OpenVAT says it works best with forward rendering and that lit materials may show lighting issues without it (Blender Extensions: OpenVAT).

#Video tutorials

#Use in recent games

• Gord (published by Team17, 2023). Pingle Studio used VATs for combat effects of the game's elemental spirits, including a body icing over and shattering, a victim cracking into fragments, and the Mimic morphing from resources into a combat form; it adds "We also used VAT for many other effects, like splashes of blood, mucus, etc." (Pingle Studio blog: How to Breathe Life into Your Game Characters…)
• Crowd and VFX practice outside a named game. SuperNatural Studios presented its Houdini-to-Unreal crowd workflow at SideFX (SideFX talks: Vertex Animation Textures for Crowds), and SideFX's own tutorials show rigid-body and fluid VATs in Unreal (SideFX tutorials: Vertex Animation Textures in Unreal).

#In different tools

• Houdini: Labs Vertex Animation Textures ROP, four modes, Unreal and Unity shaders included (Houdini documentation: Labs Vertex Animation Textures 3.0 render node).
• Blender: OpenVAT add-on, GPL, with Unity, Unreal and Godot starter content (Blender Extensions: OpenVAT).
• Unreal Engine: the AnimToTexture plugin bakes skeletal animation to VATs inside the editor (ArtStation: Zombie Horde with Vertex Animated Textures…; YouTube: VAT - Unreal Engine 5. Vertex Animation…); SideFX supplies material functions for Houdini exports (SideFX tutorials: Vertex Animation Textures in Unreal).
• Unity: SideFX's shaders, or the OpenVAT package (Houdini documentation: Labs Vertex Animation Textures 3.0 render node; Blender Extensions: OpenVAT).
• Godot: OpenVAT provides starter content, with min/max values entered by hand (Blender Extensions: OpenVAT).

Related: shaders for artists · instancing · wind and world position offset · channel packing · bit depth and banding · the technical artist

#Further reading and watching