Generates surface tangent and bitangent data for the mesh based on its vertex position and texture coordinate data.
- iOS 9.0+
- macOS 10.11+
- tvOS 9.0+
- Model I/O
The name of the vertex attribute from which to read texture coordinate data for use in generating tangent and bitangent vectors.
The name of the vertex attribute for storing surface tangent vector data.
The name of the vertex attribute for storing surface bitangent vector data.
Surface-space tangent and bitangent vectors can be used to produce shading effects that follow the “flow” of a surface or to generate normal map textures. Model I/O calculates tangent and bitangent vectors based on vertex positions and texture coordinates using a common definition: The tangent vector at a point is tangent to the surface and parallel to the texture coordinate s-axis, and the bitangent vector is tangent to the surface and parallel to the texture coordinate t-axis.
For this method to calculate surface tangent vectors, the mesh must contain vertex data for both the
MDLVertex attribute and the texture coordinate attribute specified in the
texture parameter. Calling this method on a mesh that does not contain the specified vertex attributes raises an exception.
This method saves calculated normal data in the vertex attributes named in the
bitangent parameters. If the mesh already contains either attribute, this method overwrites the contents of the corresponding vertex buffers. If the mesh does not contain an attribute, this method creates a new attribute and updates the mesh’s
vertex object accordingly.