Vector layout of tangents in IVertexDataLike

kzhsw · August 27, 2025, 12:23am

In IVertexDataLike, tangents are defined as “An array of the x, y, z tangent vector”.

packages/dev/core/src/Meshes/mesh.vertexData.ts

748afe1c8


      
           * An array of the x, y, z position of each vertex  [...., x, y, z, .....]

           */

          positions: Nullable<FloatArray>;

          

          /**

           * An array of the x, y, z normal vector of each vertex  [...., x, y, z, .....]

           */

          normals?: Nullable<FloatArray>;

          

          /**

           * An array of the x, y, z tangent vector of each vertex  [...., x, y, z, .....]

           */

          tangents?: Nullable<FloatArray>;

          

          /**

           * An array of u,v which maps a texture image onto each vertex  [...., u, v, .....]

           */

          uvs?: Nullable<FloatArray>;

          

          /**

           * A second array of u,v which maps a texture image onto each vertex  [...., u, v, .....]

But in gltf spec, tangents are defined as “XYZW vertex tangents”.

Is there a diff in vertex layout, or are there some internal conversions made during loading?

sebavan · August 27, 2025, 2:46pm

tangents are xyzw this is a doc issue, do you want to do a PR ?

kzhsw · August 28, 2025, 2:10am

Here it is:

github.com/BabylonJS/Babylon.js

Update tangents doc of VertexData

master ← kzhsw:patch-1

opened 02:10AM - 28 Aug 25 UTC

kzhsw

+2 -2

It should be vec4 of xyzw per gltf spec. > XYZW vertex tangents where the XYZ… portion is normalized, and the W component is a sign value (-1 or +1) indicating handedness of the tangent basis Also note that tangents for morph targets are vec3. Forum post: <https://forum.babylonjs.com/t/vector-layout-of-tangents-in-ivertexdatalike/60259> GLTF spec: <https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#meshes-overview>

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Vector layout of tangents in IVertexDataLike

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