Add in a tangent vector to GT_surface so that we can support bump mapping in materials.  Only generate texture coordinates and tangent vector when a texture_field is specified (removing old arc length based coordinates). Support streamlines in 2D elements with both 2D and 3D coordinates, generalising calculate_delta_xi and changing all the field conditionals.
Add in a tangent vector to GT_surface so that we can support bump mapping in
materials.  Only generate texture coordinates and tangent vector when a
texture_field is specified (removing old arc length based coordinates).
Support streamlines in 2D elements with both 2D and 3D coordinates,
generalising calculate_delta_xi and changing all the field conditionals.


git-svn-id: 4705079bc6b8aadf675e3696f5c015a6aa4916e3@2940 3c1deb5b-d424-0410-962d-aba41a686d42

hsorby/zinc,hsorby/zinc,hsorby/zinc,OpenCMISS/zinc,hsorby/zinc,OpenCMISS/zinc,OpenCMISS/zinc,OpenCMISS/zinc