More updates to GLImageObject display resolution calculation, as it

was still not ideal in many situations. Hopefully this approach will
prove to be a good one.

fsl/fsleyes/gl/globject.py

@@ -380,23 +380,36 @@ class GLImageObject(GLObject):
         ``GLImageObject``.
         """
 
-        image   = self.image
-        opts    = self.displayOpts
-        res     = opts.resolution 
-        
-        if opts.transform in ('id', 'pixdim'):
-
-            pixdim = np.array(image.pixdim[:3])
-            steps  = [res, res, res] / pixdim
-            steps  = np.maximum(steps, [1, 1, 1])
-            res    = image.shape[:3] / steps
-            
-            return np.array(res.round(), dtype=np.uint32)
-        
-        else:
-            lo, hi = map(np.array, self.getDisplayBounds())
-            maxres = int(round(((hi - lo) / res).max()))
-            return [maxres] * 3
+        import nibabel as nib
+
+        image = self.image
+        opts  = self.displayOpts
+        res   = opts.resolution
+
+        # Figure out a good display resolution
+        # along each voxel dimension
+        pixdim = np.array(image.pixdim[:3])
+        steps  = [res, res, res] / pixdim
+        steps  = np.maximum(steps, [1, 1, 1])
+        res    = image.shape[:3] / steps
+
+        # Make sure the pixel
+        # resolutions are integers
+        res = np.array(res.round(), dtype=np.uint32)
+
+        # Figure out an approximate 
+        # correspondence between the
+        # voxel axes and the display
+        # coordinate system axes. 
+        xform = opts.getTransform('id', 'display')
+        axes  = nib.orientations.aff2axcodes(
+            xform, ((0, 0), (1, 1), (2, 2)))
+
+        # Re-order the voxel resolutions
+        # in the display space
+        res = [res[axes[0]], res[axes[1]], res[axes[2]]]
+
+        return res
 
         
     def generateVertices(self, zpos, xform):

fsl/fsleyes/gl/glvolume.py

@@ -183,6 +183,9 @@ class GLVolume(globject.GLImageObject):
             fslgl.glvolume_funcs.updateShaderState(self)
             self.onUpdate()
 
+        def update(*a):
+            self.onUpdate()
+
         def imageUpdate(*a):
             volume     = opts.volume
             resolution = opts.resolution
@@ -207,6 +210,7 @@ class GLVolume(globject.GLImageObject):
         opts   .addListener('volume',         lName, imageUpdate,   weak=False)
         opts   .addListener('resolution',     lName, imageUpdate,   weak=False)
         opts   .addListener('interpolation',  lName, imageUpdate,   weak=False)
+        opts   .addListener('transform',      lName, update,        weak=False)
 
         if opts.getParent() is not None:
             opts.addSyncChangeListener(
@@ -237,6 +241,7 @@ class GLVolume(globject.GLImageObject):
         opts   .removeListener(          'volume',         lName)
         opts   .removeListener(          'resolution',     lName)
         opts   .removeListener(          'interpolation',  lName)
+        opts   .removeListener(          'transform',      lName)
         if opts.getParent() is not None:
             opts.removeSyncChangeListener('volume',        lName)
             opts.removeSyncChangeListener('resolution',    lName)