Add rendering interface for surface object (no implementation yet). * * * Add surface properties. * * * Add cdata -> RGB color conversion function. Use it in surface objects. * * * Add normals automatic computation to surface objects. * * * Make sure the correct "get" method is called. * * * Extend scaler interface to accept NDArray. * * * Surface rendering (1st part). * * * Fix wrong indexing. * * * Fix bug in xget_ancestor argument declaration. * * * Initialize OpenGL context correctly. Fix bug in surface rendering. * * * Set material color when rendering surface facets. * * * Add rendering of surface mesh and markers.