Hacky way to get the displayRange sliders to have the data range as

their limits.

fsl/fsleyes/controls/overlaydisplaypanel.py

@@ -226,6 +226,23 @@ class OverlayDisplayPanel(fslpanel.FSLEyesPanel):
             if isinstance(target, displayctx.VolumeOpts) and \
                p.key == 'cmap':
                 widget = self.__buildColourMapWidget(widget)
+
+            if isinstance(target, displayctx.VolumeOpts) and \
+               p.key == 'displayRange':
+                
+                # This is a big hack. The VolumeOpts displayRange
+                # has limits which are much bigger than the data
+                # range, due to the relationship between display
+                # range and brightness/contrast. But we want the
+                # display range sliders to have the data range as
+                # their limits. You should think of a nicer way
+                # to do this.
+                log.debug('Forcing displayRange slider range to data '
+                          'range: [{:0.3f}, {:0.3f}]'.format(
+                              target.dataMin, target.dataMax))
+                
+                widget.GetChildren()[0].SetLimits(target.dataMin,
+                                                  target.dataMax)
                 
             widgets.append(widget)