[WIP][FIX] allow non-symmetric cbar with plotly

nilearn/plotting/js_plotting_utils.py

@@ -76,8 +76,8 @@ def colorscale(cmap, values, threshold=None, symmetric_cmap=True,
         warnings.warn('you have specified symmetric_cmap=False '
                       'but the map contains negative values; '
                       'setting symmetric_cmap to True',
-                      stacklevel=3)
-        symmetric_cmap = True
+                      stacklevel=4)
+        # symmetric_cmap = True
     if symmetric_cmap and vmin is not None:
         warnings.warn('vmin cannot be chosen when cmap is symmetric',
                       stacklevel=3)

nilearn/plotting/surf_plotting.py

@@ -1143,6 +1143,10 @@ def plot_surf_stat_map(surf_mesh, stat_map, bg_map=None,
     """
     loaded_stat_map = load_surf_data(stat_map)
 
+    symmetric_cmap = True
+    if engine == "plotly" and not symmetric_cbar:
+        symmetric_cmap = False
+
     # Call get_colorbar_and_data_ranges to derive symmetric vmin, vmax
     # And colorbar limits depending on symmetric_cbar settings
     cbar_vmin, cbar_vmax, vmin, vmax = get_colorbar_and_data_ranges(
@@ -1156,7 +1160,7 @@ def plot_surf_stat_map(surf_mesh, stat_map, bg_map=None,
         surf_mesh, surf_map=loaded_stat_map,
         bg_map=bg_map, hemi=hemi,
         view=view, engine=engine, avg_method='mean', threshold=threshold,
-        cmap=cmap, symmetric_cmap=True, colorbar=colorbar,
+        cmap=cmap, symmetric_cmap=symmetric_cmap, colorbar=colorbar,
         cbar_tick_format=cbar_tick_format, alpha=alpha,
         bg_on_data=bg_on_data, darkness=darkness,
         vmax=vmax, vmin=vmin,

tmp.py

@@ -0,0 +1,58 @@
+"""Test plotting asymmetric color bar."""
+
+import matplotlib.pyplot as plt
+import numpy as np
+
+from nilearn import datasets, plotting, surface
+from nilearn.image import threshold_img
+
+stat_img = datasets.load_sample_motor_activation_image()
+stat_img = threshold_img(
+    stat_img,
+    threshold=2,
+    cluster_threshold=0,
+    two_sided=False,
+    copy=True,
+)
+
+fsaverage = datasets.fetch_surf_fsaverage()
+
+curv_right = surface.load_surf_data(fsaverage.curv_right)
+curv_right_sign = np.sign(curv_right)
+
+texture = surface.vol_to_surf(stat_img, fsaverage.pial_right)
+
+engine = "matplotlib"
+
+plotting.plot_surf_stat_map(
+    fsaverage.infl_right,
+    texture,
+    hemi="right",
+    title="Surface right hemisphere",
+    colorbar=True,
+    threshold=1.0,
+    bg_map=curv_right_sign,
+    engine=engine,
+    symmetric_cbar=False,
+    cmap="black_red",
+)
+plt.show()
+
+engine = "plotly"
+
+print(f"Using plotting engine {engine}.")
+
+fig = plotting.plot_surf_stat_map(
+    fsaverage.infl_right,
+    texture,
+    hemi="right",
+    title="Surface right hemisphere",
+    colorbar=True,
+    threshold=1.0,
+    bg_map=curv_right_sign,
+    bg_on_data=True,
+    engine=engine,
+    symmetric_cbar=False,
+    cmap="black_red",
+)
+fig.show()