addTangentBasis(forTextureCoordinateAttributeNamed:normalAttributeNamed:tangentAttributeNamed:)
Generates surface tangent data for the mesh based on its vertex position, surface normal, and texture coordinate data.
Declaration
func addTangentBasis(forTextureCoordinateAttributeNamed textureCoordinateAttributeName: String, normalAttributeNamed normalAttributeName: String, tangentAttributeNamed tangentAttributeName: String)Parameters
- textureCoordinateAttributeName:
The name of the vertex attribute from which to read texture coordinate data.
- normalAttributeName:
The name of the vertex attribute from which to read surface normal data.
- tangentAttributeName:
The name of the vertex attribute for storing surface tangent vector data.
Discussion
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 vectors based on vertex positions, texture coordinates, and surface normal vectors using a common definition: The tangent vector at a point is tangent to the surface, perpendicular to the surface normal vector, and parallel to the texture coordinate s-axis.
For this method to calculate surface tangent vectors, the mesh must contain vertex data for both the MDLVertexAttributePosition attribute and the texture coordinate attribute specified in the textureCoordinateAttributeName 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 attribute named in the tangentAttributeName parameter. If the mesh already contains that attribute, this method overwrites the contents of the corresponding vertex buffer. If the mesh does not contain that attribute, this method creates a new attribute and updates the mesh’s vertexDescriptor object accordingly.