Setting cell data scalars through set_active_attribute not working

[JulieWinchester]

Hello,

After updating to Mayavi 4.4.3 and VTK 6.3 using Python 2.7.10 on OSX 10.10, I've noticed that coloring triangular meshes by polygon face (as in examples here or here) no longer seems to work. Any attempt to pass a cell_scalars name to set_active_attribute now produces an error of the form:

Traceback (most recent call last):

File "GUItestbed.py", line 35, in <module> 
    mesh = mlab.pipeline.set_active_attribute(wire_mesh, cell_scalars='Cell data')

File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/mayavi/tools/pipe_base.py", line 38, in the_function
    factory = factory_class(*args, **kwargs)

File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/mayavi/tools/pipe_base.py", line 163, in __init__
    self.set(**traits)

File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/mayavi/tools/pipe_base.py", line 180, in set
    self._anytrait_changed(trait, value)

File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/mayavi/tools/pipe_base.py", line 198, in _anytrait_changed
    setattr(obj, components[-1], value)

File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/mayavi/core/trait_defs.py", line 107, in set_value
    value )
traits.trait_errors.TraitError: The 'cell_scalars_name' trait of a SetActiveAttribute instance must be one of [''], but a value of 'Cell data' <type 'str'> was specified.

Is this a bug, or is there now a different way to go about assigning colors using cell data? This method definitely worked in older versions of Mayavi.

Thanks!
Julia

[JulieWinchester]

I found the solution to this problem, it has to do with newer versions of Mayavi and/or VTK updating mlab source datasets slightly differently than older versions. I noticed a change between the current Github atomic orbital example and the version on the Mayavi site. A similar change to mlab dataset updates makes coloring triangulated meshes by polygon using set_active_attribute functional again. Below I'm including a version of the first script linked above in a form that now works with Mayavi 4.4.3 and VTK 6.3.0.

import numpy as np 
from mayavi import mlab 

# Create cone 
n = 8 
t = np.linspace(-np.pi, np.pi, n) 
z = np.exp(1j*t) 
x = z.real.copy() 
y = z.imag.copy() 
z = np.zeros_like(x) 
triangles = [(0, i, i+1) for i in range(n)] 
x = np.r_[0, x] 
y = np.r_[0, y] 
z = np.r_[1, z] 
t = np.r_[0, t] 

# These are the scalar values for each triangle 
f = np.mean(t[np.array(triangles)], axis=1) 

# Plot it 
mesh = mlab.triangular_mesh(x, y, z, triangles, 
                            representation='wireframe', 
                            opacity=0) 
mesh.mlab_source.dataset.cell_data.scalars = f 
mesh.mlab_source.dataset.cell_data.scalars.name = 'Cell data' 
mesh.mlab_source.update() 

mesh2 = mlab.pipeline.set_active_attribute(mesh, 
        cell_scalars='Cell data') 
mlab.pipeline.surface(mesh2) 

mlab.show()