Allow distance override for multi-panel detectors (cctbx#698)

Allow distance override for multi-panel detectors. If a multi-panel detector has a hierarchy, it will have its root node distance set. If there is no hierarchy then each panel will individually have distance set, but only if those panels are coplanar and already at the same distance.

newsfragments/698.feature

@@ -0,0 +1 @@
+Manual override of the detector distance is now available for multi-panel detectors.

src/dxtbx/model/detector_helpers.py

@@ -303,15 +303,34 @@ def set_detector_distance(detector, distance):
     """
     Set detector origin from distance along normal
     """
-    assert len(detector) == 1
-    normal = matrix.col(detector[0].get_normal())
-    origin = matrix.col(detector[0].get_origin())
-    d = origin.dot(normal)
-    x = origin - d * normal
-    origin = distance * normal + x
-    fast_axis = detector[0].get_fast_axis()
-    slow_axis = detector[0].get_slow_axis()
-    detector[0].set_frame(fast_axis, slow_axis, origin)
+    # If the detector has a hierarchy, just update the root note
+    try:
+        h = detector.hierarchy()
+        normal = matrix.col(h.get_normal())
+        origin = matrix.col(h.get_origin())
+        d = origin.dot(normal)
+        x = origin - d * normal
+        origin = distance * normal + x
+        fast_axis = h.get_fast_axis()
+        slow_axis = h.get_slow_axis()
+        h.set_frame(fast_axis, slow_axis, origin)
+    except AttributeError:
+        # Check all panels are at the same distance and share the same normal
+        dists = [p.get_distance() for p in detector]
+        norm_vecs = [p.get_normal() for p in detector]
+        assert all(v == norm_vecs[0] for v in norm_vecs[1:]) and all(
+            d == dists[0] for d in dists
+        )
+
+        for panel in detector:
+            normal = matrix.col(panel.get_normal())
+            origin = matrix.col(panel.get_origin())
+            d = origin.dot(normal)
+            x = origin - d * normal
+            origin = distance * normal + x
+            fast_axis = panel.get_fast_axis()
+            slow_axis = panel.get_slow_axis()
+            panel.set_frame(fast_axis, slow_axis, origin)
 
 
 def get_detector_projection_2d_axes(