Allow users to register custom matplotlib colormaps

[rosswhitfield]

Description of work

This apparently work previously but stopped working at some point. The problem is that the list of available colormaps is initialized once when ColorbarWidget is first imported and we have users that like loaded register new colormaps in their scripts. This change makes it work again.

Summary of work

Fixes 8690: [Defect] Add MDF colormap to workbench and slice viewer

Further detail of work

To test:

from mantid.simpleapi import *
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.colors import ListedColormap

plt.colormaps.register(cmap=ListedColormap([[0, 0, 0], [0, 0, 1], [0, 1, 0], [1, 0, 0], [1,1,1]]), name="CUSTOM_MAP")

S  =range(0,100);
ERR=range(0,100);
ws=CreateMDHistoWorkspace(Dimensionality=2,Extents='-10,10,-10,10',SignalInput=S,ErrorInput=ERR,\
                           NumberOfBins='10,10',Names='Dim1,Dim2',Units='MomentumTransfer,EnergyTransfer')

then open ws with Sliceviewer and check if CUSTOM_MAP is now one of the available Colormaps.

This will throw an error if you select the Reverse option unless a map named CUSTOM_MAP_r is also added.

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[sf1919]

Would it be possible to provide a bit more information about the work? Unfortunately unless we work at ORNL we can't access the linked issue. As this is functionality that is not ORNL specific there is wider interest.

[zjmorgan]

Would it be possible to provide a bit more information about the work? Unfortunately unless we work at ORNL we can't access the linked issue. As this is functionality that is not ORNL specific there is wider interest.

User's previously could modify the listed colormaps in Matplotlib by overwriting one of the default maps using their own custom map file of RGB values. Matplotlib now does not let the maps to be overwritten, so this doesn't work. This issue makes it possible to define a separate custom map that can be read into sliceviewer.

[zjmorgan]

import matplotlib.pyplot as plt
import numpy as np

from matplotlib.colors import ListedColormap, LinearSegmentedColormap
from matplotlib import cm

from mantid.simpleapi import *

# Load map file
Cmap_Name = 'MDF' # Colormap name
Loaded_Cmap = np.loadtxt('/HFIR/HB2C/shared/WANDscripts/colormaps/MDF.map')/255

# Register the loaded Colormap
Listed_CustomCmap = ListedColormap(Loaded_Cmap, name=Cmap_Name)

# Create and register the reverse colormap
Listed_CustomCmap_r = ListedColormap(Loaded_Cmap[::-1,:], name=(Cmap_Name + '_r') )

cm.register_cmap(name=Cmap_Name, cmap=Listed_CustomCmap, override_builtin=True)
cm.register_cmap(name=(Cmap_Name + '_r'), cmap= Listed_CustomCmap_r, override_builtin=True)   

ws = CreateMDWorkspace(Dimensions='3', 
                       EventType='MDEvent', 
                       Extents='-10,10,-5,5,-1,1',
                       Names='Q_lab_x,Q_lab_y,Q_lab_z', 
                       Units='1\A,1\A,1\A')
FakeMDEventData(ws, UniformParams="1000000")

works well. Thank you for this!

[zjmorgan]

Small thing:

If you set the new map to default, close workbench and re-open workbench, you cannot open sliceviewer if the map is not reloaded. Can we just default back to viridis so at least the user can reopen sliceviewer?