What are Apple's Metal (Metal Shader Language) texture coordinates?

In iOS or OS/X what texture coordinates are used in Metal Shader Language kernel function? For example, given an MTLTexture and uint2 gid[[thread_position_in_grid]] Is gid.x and gid.ybetween 0..1 (x and y are floats) or 0..inTexture.get_width() (x and y are integers).

Thanks in Advance