I think you want to use point data instead of cell data. With cell data, a single scalar value is not localized to any point. It is assigned to the entire face. It looks like you just want to assign the t
data to the vertices instead. The default rendering of point scalars will smoothly interpolate across each face.
point_data = mesh.mlab_source.dataset.point_data
point_data.scalars = t
point_data.scalars.name = 'Point data'
point_data.update()
mesh2 = mlab.pipeline.set_active_attribute(mesh,
point_scalars='Point data')