This is a repository that contains examples of the use of VAT (Vertex Animation Texture) on Unity High Definition Render Pipeline (HDRP).
In this document, "VAT" refers explicitly to the texture encoding method used in Houdini's Game Development Toolset.
- Unity 2019.3
- HDRP 7.1
- The Shader Graph example only supports the "Soft (Consistent Topology)" method.
- The Visual Effect Graph example only supports the "Sprite (Camera Facing Cards)" method.
At first, export textures (.exr) and a static mesh (.fbx) from Houdini using
the VAT exporter and import those files into Unity. Note that the texture files
should be imported as raw SFloat textures (see the screenshot below for
detailed import settings).
You can use a shader graph named "Shader Graph/Cloth" to animate the mesh.
The "BBOX MIN"/"BBOX MAX" and "Number of Frames" properties must be set based on the export settings. These BBOX values are shown in Houdini when an exporting is done. When calculating the number of frames, note that you shouldn't take the last frame into account. For example, when the start frame is 1, and the end frame is 100, the "Number of Frames" must be set to 99.
You can also use the packed-normal encoding where the exporter embeds normal vectors into the alpha channel of the position map. To use this option, enable "Use Packed Normal" and unset the Normal Map property.
To animate the mesh, you have to control the "Current Frame" property manually. In the "Cloth" example, this property is controlled by a timeline.
The structure of the shader graph is quite simple. You can easily extend it to add features, like adding a color map or support of different surface types.
As same as the Shader Graph example, VAT textures should be imported as raw SFloat textures.
You can use a custom subgraph block named "Set VAT Attributes" that updates the position and color attributes based on the given VATs.
Note that a sprite VAT can contain "texture size * 3" particles. It should initially emit "texture size * 3" particles using the Single Burst block.
It depends on the case -- It may work with an acceptable amount of errors in some cases, but it may glitch in some other cases. A trial-and-error approach would be required.