Fix for Matplotlib barriers not plotting correctly

CHANGELOG.rst

@@ -23,6 +23,7 @@ The format is based on `Keep a Changelog`_.
 Added
 -----
 
+
 - New EnlargeWithAncilla pass for adding ancilla qubits after a Layout
   selection pass (#1603).
 - New Unroll2Q pass for unrolling gates down to just 1q or 2q gates (#1614). 
@@ -58,6 +59,7 @@ Fixed
 
 - Fixed a bug with measurement sampling optimization in BasicAer
   qasm_simulator (#1624).
+- Fixed a bug where barriers didn't plot over all qubits when using matplotlib.
 - Fixed a minor conda env bug in Makefile (#1691).
 - Fixed a bug in BasicMapper pass operating over multiple registers (#1611).
 - Fixed a bug in BarrierBeforeFinalMeasurements which incorrectly moved measurements

qiskit/tools/visualization/_matplotlib.py

@@ -483,6 +483,7 @@ def _draw_ops(self, verbose=False):
         #
         for i, (op, op_next) in enumerate(
                 itertools.zip_longest(self._ops, next_ops)):
+
             # wide gate
             if op['name'] in _wide_gate:
                 _iswide = True
@@ -501,6 +502,7 @@ def _draw_ops(self, verbose=False):
                             break
             else:
                 q_idxs = []
+
             # get creg index
             if 'cargs' in op.keys():
                 c_idxs = []
@@ -512,6 +514,7 @@ def _draw_ops(self, verbose=False):
                             break
             else:
                 c_idxs = []
+
             # find empty space to place gate
             if not _barriers['group']:
                 this_anc = max([q_anchors[ii].get_index() for ii in q_idxs])
@@ -592,10 +595,15 @@ def _draw_ops(self, verbose=False):
                 self._measure(q_xy[0], c_xy[0], vv)
             elif op['name'] in ['barrier', 'snapshot', 'load', 'save',
                                 'noise']:
-                q_group = self._qreg_dict[q_idxs[0]]['group']
-                if q_group not in _barriers['group']:
-                    _barriers['group'].append(q_group)
-                _barriers['coord'].append(q_xy[0])
+
+                # Go over all indices to add barriers across
+                for index in range(len(q_idxs)):
+                    q_group = self._qreg_dict[q_idxs[index]]['group']
+
+                    if q_group not in _barriers['group']:
+                        _barriers['group'].append(q_group)
+                    _barriers['coord'].append(q_xy[index])
+
                 if op_next and op_next['name'] == 'barrier':
                     continue
                 else: