The mapping channel to be used for a texture coordinate semantic.
- iOS 8.0+
- macOS 10.8+
- tvOS 9.0+
This key can be used with the
options dictionary for the
set method, and applies only to the
texcoord semantic. Its value is an
NSNumber object containing an unsigned integer value.
A geometry can provide, and a shader program can use, more than one source of texture coordinates for each vertex. Use this key to specify which geometry source should provide data for each texture sampler vertex attribute declared in a shader program. The mapping channel for a geometry source corresponds to its index in the array returned by calling the