Support for cregbundle in text circuit drawer (#4274)

* drafting

* size

* layer is cregbundle aware

* test

* expose it in .draw()

* print

* scale docstring

* lint

* test adjustment

* multiple cregs

* lint

* conditional

* lint

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit/circuit/quantumcircuit.py

@@ -749,7 +749,7 @@ def qasm(self, formatted=False, filename=None):
     def draw(self, output=None, scale=0.7, filename=None, style=None,
              interactive=False, line_length=None, plot_barriers=True,
              reverse_bits=False, justify=None, vertical_compression='medium', idle_wires=True,
-             with_layout=True, fold=None, ax=None, initial_state=False):
+             with_layout=True, fold=None, ax=None, initial_state=False, cregbundle=True):
         """Draw the quantum circuit.
 
         **text**: ASCII art TextDrawing that can be printed in the console.
@@ -822,6 +822,8 @@ def draw(self, output=None, scale=0.7, filename=None, style=None,
             initial_state (bool): Optional. Adds ``|0>`` in the beginning of the wire.
                 Only used by the ``text``, ``latex`` and ``latex_source`` outputs.
                 Default: ``False``.
+            cregbundle (bool): Optional. If set True bundle classical registers. Only used by
+                the ``text`` output. Default: ``True``.
 
         Returns:
             :class:`PIL.Image` or :class:`matplotlib.figure` or :class:`str` or
@@ -964,7 +966,8 @@ def draw(self, output=None, scale=0.7, filename=None, style=None,
                               with_layout=with_layout,
                               fold=fold,
                               ax=ax,
-                              initial_state=initial_state)
+                              initial_state=initial_state,
+                              cregbundle=cregbundle)
 
     def size(self):
         """Returns total number of gate operations in circuit.

qiskit/visualization/circuit_visualization.py

@@ -65,7 +65,8 @@ def circuit_drawer(circuit,
                    with_layout=True,
                    fold=None,
                    ax=None,
-                   initial_state=False):
+                   initial_state=False,
+                   cregbundle=True):
     """Draw a quantum circuit to different formats (set by output parameter):
 
     **text**: ASCII art TextDrawing that can be printed in the console.
@@ -78,7 +79,8 @@ def circuit_drawer(circuit,
 
     Args:
         circuit (QuantumCircuit): the quantum circuit to draw
-        scale (float): scale of image to draw (shrink if < 1)
+        scale (float): scale of image to draw (shrink if < 1). Only used by the ``mpl``,
+            ``latex``, and ``latex_source`` outputs.
         filename (str): file path to save image to
         style (dict or str): dictionary of style or file name of style file.
             This option is only used by the ``mpl`` output type. If a str is
@@ -137,6 +139,8 @@ def circuit_drawer(circuit,
         initial_state (bool): Optional. Adds ``|0>`` in the beginning of the wire.
             Only used by the ``text``, ``latex`` and ``latex_source`` outputs.
             Default: ``False``.
+        cregbundle (bool): Optional. If set True bundle classical registers. Only used by
+            the ``text`` output. Default: ``True``.
     Returns:
         :class:`PIL.Image` or :class:`matplotlib.figure` or :class:`str` or
         :class:`TextDrawing`:
@@ -286,7 +290,8 @@ def circuit_drawer(circuit,
                                     idle_wires=idle_wires,
                                     with_layout=with_layout,
                                     fold=fold,
-                                    initial_state=initial_state)
+                                    initial_state=initial_state,
+                                    cregbundle=cregbundle)
     elif output == 'latex':
         image = _latex_circuit_drawer(circuit, scale=scale,
                                       filename=filename, style=style,
@@ -406,7 +411,8 @@ def qx_color_scheme():
 
 def _text_circuit_drawer(circuit, filename=None, line_length=None, reverse_bits=False,
                          plot_barriers=True, justify=None, vertical_compression='high',
-                         idle_wires=True, with_layout=True, fold=None, initial_state=True):
+                         idle_wires=True, with_layout=True, fold=None, initial_state=True,
+                         cregbundle=False):
     """Draws a circuit using ascii art.
 
     Args:
@@ -428,6 +434,8 @@ def _text_circuit_drawer(circuit, filename=None, line_length=None, reverse_bits=
                     `shutil.get_terminal_size()`. If you don't want pagination
                    at all, set `fold=-1`.
         initial_state (bool): Optional. Adds |0> in the beginning of the line. Default: `True`.
+        cregbundle (bool): Optional. If set True bundle classical registers. Only used by
+            the ``text`` output. Default: ``False``.
     Returns:
         TextDrawing: An instances that, when printed, draws the circuit in ascii art.
     """
@@ -442,7 +450,8 @@ def _text_circuit_drawer(circuit, filename=None, line_length=None, reverse_bits=
     if line_length:
         warn('The parameter "line_length" is being replaced by "fold"', DeprecationWarning, 3)
         fold = line_length
-    text_drawing = _text.TextDrawing(qregs, cregs, ops, layout=layout, initial_state=initial_state)
+    text_drawing = _text.TextDrawing(qregs, cregs, ops, layout=layout, initial_state=initial_state,
+                                     cregbundle=cregbundle)
     text_drawing.plotbarriers = plot_barriers
     text_drawing.line_length = fold
     text_drawing.vertical_compression = vertical_compression

qiskit/visualization/text.py

@@ -171,11 +171,11 @@ class MeasureTo(DrawElement):
         bot:
     """
 
-    def __init__(self):
+    def __init__(self, label=''):
         super().__init__()
         self.top_connect = " ║ "
         self.mid_content = "═╩═"
-        self.bot_connect = "   "
+        self.bot_connect = label
         self.mid_bck = "═"
 
 
@@ -500,13 +500,15 @@ class TextDrawing():
     """ The text drawing"""
 
     def __init__(self, qregs, cregs, instructions, plotbarriers=True,
-                 line_length=None, vertical_compression='high', layout=None, initial_state=True):
+                 line_length=None, vertical_compression='high', layout=None, initial_state=True,
+                 cregbundle=False):
         self.qregs = qregs
         self.cregs = cregs
         self.instructions = instructions
         self.layout = layout
         self.initial_state = initial_state
 
+        self.cregbundle = cregbundle
         self.plotbarriers = plotbarriers
         self.line_length = line_length
         if vertical_compression not in ['high', 'medium', 'low']:
@@ -641,9 +643,19 @@ def wire_names(self, with_initial_state=False):
                                                  index=self.layout[bit.index].index,
                                                  physical=bit.index))
         clbit_labels = []
+        previous_creg = None
         for bit in self.cregs:
-            label = '{name}_{index}: ' + initial_clbit_value
-            clbit_labels.append(label.format(name=bit.register.name, index=bit.index))
+            if self.cregbundle:
+                if previous_creg == bit.register:
+                    continue
+                previous_creg = bit.register
+                label = '{name}: {initial_value}{size}/'
+                clbit_labels.append(label.format(name=bit.register.name,
+                                                 initial_value=initial_clbit_value,
+                                                 size=bit.register.size))
+            else:
+                label = '{name}_{index}: ' + initial_clbit_value
+                clbit_labels.append(label.format(name=bit.register.name, index=bit.index))
         return qubit_labels + clbit_labels
 
     def should_compress(self, top_line, bot_line):
@@ -798,6 +810,8 @@ def merge_lines(top, bot, icod="top"):
                 ret += "┬"
             elif topc in "┘└" and botc in "─" and icod == 'top':
                 ret += "┴"
+            elif botc == " " and icod == 'top':
+                ret += topc
             else:
                 ret += botc
         return ret
@@ -899,7 +913,10 @@ def add_connected_gate(instruction, gates, layer, current_cons):
         elif isinstance(instruction.op, MeasureInstruction):
             gate = MeasureFrom()
             layer.set_qubit(instruction.qargs[0], gate)
-            layer.set_clbit(instruction.cargs[0], MeasureTo())
+            if self.cregbundle:
+                layer.set_clbit(instruction.cargs[0], MeasureTo(str(instruction.cargs[0].index)))
+            else:
+                layer.set_clbit(instruction.cargs[0], MeasureTo())
 
         elif isinstance(instruction.op, (BarrierInstruction, Snapshot)):
             # barrier
@@ -1002,7 +1019,7 @@ def build_layers(self):
         layers = [InputWire.fillup_layer(wire_names)]
 
         for instruction_layer in self.instructions:
-            layer = Layer(self.qregs, self.cregs)
+            layer = Layer(self.qregs, self.cregs, self.cregbundle)
 
             for instruction in instruction_layer:
                 layer, current_connections, connection_label = \
@@ -1018,12 +1035,22 @@ def build_layers(self):
 class Layer:
     """ A layer is the "column" of the circuit. """
 
-    def __init__(self, qregs, cregs):
+    def __init__(self, qregs, cregs, cregbundle=False):
         self.qregs = qregs
-        self.cregs = cregs
+        if cregbundle:
+            self.cregs = []
+            previous_creg = None
+            for bit in cregs:
+                if previous_creg == bit.register:
+                    continue
+                previous_creg = bit.register
+                self.cregs.append(bit.register)
+        else:
+            self.cregs = cregs
         self.qubit_layer = [None] * len(qregs)
         self.connections = []
         self.clbit_layer = [None] * len(cregs)
+        self.cregbundle = cregbundle
 
     @property
     def full_layer(self):
@@ -1050,7 +1077,10 @@ def set_clbit(self, clbit, element):
             clbit (cbit): Element of self.cregs.
             element (DrawElement): Element to set in the clbit
         """
-        self.clbit_layer[self.cregs.index(clbit)] = element
+        if self.cregbundle:
+            self.clbit_layer[self.cregs.index(clbit.register)] = element
+        else:
+            self.clbit_layer[self.cregs.index(clbit)] = element
 
     def _set_multibox(self, label, qubits=None, clbits=None, top_connect=None,
                       bot_connect=None, conditional=False, controlled_edge=None):
@@ -1154,8 +1184,11 @@ def set_cl_multibox(self, creg, label, top_connect='┴'):
             label (string): The label for the multi clbit box.
             top_connect (char): The char to connect the box on the top.
         """
-        clbit = [bit for bit in self.cregs if bit.register == creg]
-        self._set_multibox(label, clbits=clbit, top_connect=top_connect)
+        if self.cregbundle:
+            self.set_clbit(creg[0], BoxOnClWire(label=label, top_connect=top_connect))
+        else:
+            clbit = [bit for bit in self.cregs if bit.register == creg]
+            self._set_multibox(label, clbits=clbit, top_connect=top_connect)
 
     def set_qu_multibox(self, bits, label, top_connect=None, bot_connect=None,
                         conditional=False, controlled_edge=None):

test/python/visualization/test_circuit_text_drawer.py

@@ -60,6 +60,14 @@ def test_measure_to(self):
                     "   "]
         self.assertEqualElement(expected, element)
 
+    def test_measure_to_label(self):
+        """ MeasureTo element with cregbundle """
+        element = elements.MeasureTo('1')
+        expected = [" ║ ",
+                    "═╩═",
+                    " 1 "]
+        self.assertEqualElement(expected, element)
+
     def test_measure_from(self):
         """ MeasureFrom element. """
         element = elements.MeasureFrom()
@@ -124,6 +132,44 @@ def test_text_no_pager(self):
 class TestTextDrawerGatesInCircuit(QiskitTestCase):
     """ Gate by gate checks in different settings."""
 
+    def test_text_measure_cregbundle(self):
+        """ The measure operator, using 3-bit-length registers with cregbundle=True. """
+        expected = '\n'.join(["        ┌─┐      ",
+                              "q_0: |0>┤M├──────",
+                              "        └╥┘┌─┐   ",
+                              "q_1: |0>─╫─┤M├───",
+                              "         ║ └╥┘┌─┐",
+                              "q_2: |0>─╫──╫─┤M├",
+                              "         ║  ║ └╥┘",
+                              " c: 0 3/═╩══╩══╩═",
+                              "         0  1  2 "])
+
+        qr = QuantumRegister(3, 'q')
+        cr = ClassicalRegister(3, 'c')
+        circuit = QuantumCircuit(qr, cr)
+        circuit.measure(qr, cr)
+        self.assertEqual(str(_text_circuit_drawer(circuit, cregbundle=True)), expected)
+
+    def test_text_measure_cregbundle_2(self):
+        """ The measure operator, using 2 classical registers with cregbundle=True. """
+        expected = '\n'.join(["        ┌─┐   ",
+                              "q_0: |0>┤M├───",
+                              "        └╥┘┌─┐",
+                              "q_1: |0>─╫─┤M├",
+                              "         ║ └╥┘",
+                              "cA: 0 1/═╩══╬═",
+                              "         0  ║ ",
+                              "cB: 0 1/════╩═",
+                              "            0 "])
+
+        qr = QuantumRegister(2, 'q')
+        cr_a = ClassicalRegister(1, 'cA')
+        cr_b = ClassicalRegister(1, 'cB')
+        circuit = QuantumCircuit(qr, cr_a, cr_b)
+        circuit.measure(qr[0], cr_a[0])
+        circuit.measure(qr[1], cr_b[0])
+        self.assertEqual(str(_text_circuit_drawer(circuit, cregbundle=True)), expected)
+
     def test_text_measure_1(self):
         """ The measure operator, using 3-bit-length registers. """
         expected = '\n'.join(['        ┌─┐      ',
@@ -1142,6 +1188,28 @@ def test_text_measure_with_spaces(self):
 class TestTextConditional(QiskitTestCase):
     """Gates with conditionals"""
 
+    def test_text_conditional_1_cregbundle(self):
+        """ Conditional drawing with 1-bit-length regs and cregbundle."""
+        qasm_string = """
+        OPENQASM 2.0;
+        include "qelib1.inc";
+        qreg q[1];
+        creg c0[1];
+        creg c1[1];
+        if(c0==1) x q[0];
+        if(c1==1) x q[0];
+        """
+        expected = '\n'.join(["         ┌───┐  ┌───┐ ",
+                              "q_0: |0>─┤ X ├──┤ X ├─",
+                              "        ┌┴─┴─┴┐ └─┬─┘ ",
+                              "c0: 0 1/╡ = 1 ╞═══╪═══",
+                              "        └─────┘┌──┴──┐",
+                              "c1: 0 1/═══════╡ = 1 ╞",
+                              "               └─────┘"])
+
+        circuit = QuantumCircuit.from_qasm_str(qasm_string)
+        self.assertEqual(str(_text_circuit_drawer(circuit, cregbundle=True)), expected)
+
     def test_text_conditional_1(self):
         """ Conditional drawing with 1-bit-length regs."""
         qasm_string = """
@@ -1164,6 +1232,27 @@ def test_text_conditional_1(self):
         circuit = QuantumCircuit.from_qasm_str(qasm_string)
         self.assertEqual(str(_text_circuit_drawer(circuit)), expected)
 
+    def test_text_conditional_2_cregbundle(self):
+        """ Conditional drawing with 2-bit-length regs with cregbundle"""
+        qasm_string = """
+        OPENQASM 2.0;
+        include "qelib1.inc";
+        qreg q[1];
+        creg c0[2];
+        creg c1[2];
+        if(c0==2) x q[0];
+        if(c1==2) x q[0];
+        """
+        expected = '\n'.join(["         ┌───┐  ┌───┐ ",
+                              "q_0: |0>─┤ X ├──┤ X ├─",
+                              "        ┌┴─┴─┴┐ └─┬─┘ ",
+                              "c0: 0 2/╡ = 2 ╞═══╪═══",
+                              "        └─────┘┌──┴──┐",
+                              "c1: 0 2/═══════╡ = 2 ╞",
+                              "               └─────┘"])
+        circuit = QuantumCircuit.from_qasm_str(qasm_string)
+        self.assertEqual(str(_text_circuit_drawer(circuit, cregbundle=True)), expected)
+
     def test_text_conditional_2(self):
         """ Conditional drawing with 2-bit-length regs."""
         qasm_string = """
@@ -2607,7 +2696,7 @@ def test_after_transpile(self):
                         [13, 12]]
         qc_result = transpile(qc, basis_gates=['u1', 'u2', 'u3', 'cx', 'id'],
                               coupling_map=coupling_map, optimization_level=0, seed_transpiler=0)
-        self.assertEqual(qc_result.draw(output='text').single_string(), expected)
+        self.assertEqual(qc_result.draw(output='text', cregbundle=False).single_string(), expected)
 
 
 class TestTextInitialValue(QiskitTestCase):
@@ -2631,7 +2720,8 @@ def test_draw_initial_value_default(self):
                               "c_1: ════╩═",
                               "           "])
 
-        self.assertEqual(self.circuit.draw(output='text').single_string(), expected)
+        self.assertEqual(self.circuit.draw(output='text', cregbundle=False).single_string(),
+                         expected)
 
     def test_draw_initial_value_true(self):
         """ Text drawer .draw(initial_state=True). """
@@ -2644,8 +2734,9 @@ def test_draw_initial_value_true(self):
                               "            ║ ",
                               " c_1: 0 ════╩═",
                               "              "])
-        self.assertEqual(self.circuit.draw(output='text', initial_state=True).single_string(),
-                         expected)
+        self.assertEqual(self.circuit.draw(output='text',
+                                           initial_state=True,
+                                           cregbundle=False).single_string(), expected)
 
     def test_initial_value_false(self):
         """ Text drawer with initial_state parameter False. """

test/python/visualization/test_circuit_visualization_output.py

@@ -100,7 +100,8 @@ def test_matplotlib_drawer(self):
     def test_text_drawer(self):
         filename = self._get_resource_path('current_textplot.txt')
         qc = self.sample_circuit()
-        output = circuit_drawer(qc, filename=filename, output="text", fold=-1, initial_state=True)
+        output = circuit_drawer(qc, filename=filename, output="text", fold=-1, initial_state=True,
+                                cregbundle=False)
         self.assertFilesAreEqual(filename, self.text_reference)
         os.remove(filename)
         try: